Updated on 2024/06/26

写真a

 
AMANO, Hiroshi
 
Organization
Institute of Materials and Systems for Sustainability Center for Integrated Research of Future Electronics Innovative Devices Section Professor
Graduate School
Graduate School of Engineering
Undergraduate School
School of Engineering
Title
Professor
Contact information
メールアドレス
External link

Degree 7

  1. 名誉博士号 ( 2017.1   グアテマラパジェ大学 ) 

  2. 名誉博士号 ( 2016.6   モンゴル国立大学 ) 

  3. 名誉博士号 ( 2016.5   フランスオーベルニュ大学ブレイズパスカル大学 ) 

  4. 名誉博士号 ( 2016.4   イタリアパドバ大学 ) 

  5. 名誉博士号 ( 2015.9   スウェーデンリンショーピング大学 ) 

  6. 名誉博士号 ( 2015.6   ロシアノボシビルスク州立大学 ) 

  7. Doctor of Engineering ( 1989.1   Nagoya University ) 

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Research Interests 10

  1. Light emitting diodelaser diode, High power and high frequency transistor, Solar cells, Nano structure, Crystal growth of compound semiconductors, Semiconductor device physics

  2. Light emitting diodelaser diode

  3. Nano structure

  4. Semiconductor device physics

  5. Crystal growth of compound semiconductors

  6. High power and high frequency transistor

  7. ナノ構造

  8. Solar cells

  9. パワーデバイス 

  10. ミリ波 マイクロ波デバイス

Research Areas 1

  1. Others / Others  / Electrrical and Electronic Materials Engineering

Current Research Project and SDGs 3

  1. 安心・安全で省エネルギー化に貢献する半導体デバイス

  2. Crystal growth and device fabrications of group III nitride semiconductors

  3. 卓越大学院DIIプログラム

Research History 15

  1. Institute of Materials and Systems for Sustainability   Center for Integrated Research of Future Electronics   Director of CIRFE

    2015.10

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    Country:Japan

  2. Nagoya University   Institute of Materials and Systems for Sustainability Center for Integrated Research of Future Electronics Innovative Devices Section   Professor

    2015.10

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  3. 名城大学特別栄誉教授

    2015.7

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    Country:Japan

  4. Meijo University

    2015.7

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  5. 名古屋市立大学 客員教授

    2015.4 - 2016.3

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    Country:Japan

  6. 名古屋大学特別教授

    2015.3

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    Country:Japan

  7. Nagoya University   Professor

    2015.3

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  8. Tsinghua University, China   Professor Emeritus

    2014.11

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  9. Nagoya University   Graduate School of Engineering Graduate School of Engineering

    2011.4

  10. Nagoya University   Graduate School of Engineering Graduate School of Engineering

    2011.4

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  11. Nagoya University   Graduate School of Engineering, Department of Electrical Engineering and Computer Science   Professor

    2010.4 - 2015.10

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    Country:Japan

  12. Professor, Meijo University

    2002.4 - 2010.3

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    Country:Japan

  13. Associate Professor

    1998.4 - 2002.3

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    Country:Japan

  14. Assistant Professor, Meijo University

    1992.4 - 1998.3

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    Country:Japan

  15. Research Associate, Nagoya University

    1988.4 - 1992.3

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    Country:Japan

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Education 3

  1. Nagoya University   Graduate School, Division of Engineering   Department of Electrical and Electornics Engineering

    1985.4 - 1988.3

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    Country: Japan

  2. Nagoya University   Graduate School, Division of Engineering   Department of Electrical and Electronics Enginnering

    1983.4 - 1985.3

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    Country: Japan

  3. Nagoya University   Faculty of Engineering   Department of Electronics

    1979.4 - 1983.3

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    Country: Japan

Professional Memberships 34

  1. 日本学士院   会員

    2022.12

  2. IEEE   メンバー

    2022.1

  3. 中国工程院   外国籍院士

    2019.11

  4. National Academy of Inventors,USA   NAI Fellow

    2017.10

  5. 照明学会   名誉会員

    2016.9

  6. APS   Fellow

    2015.9

  7. 日本工学アカデミー   会員

    2015.6

  8. 日本化学会   名誉会員

    2015.6

  9. NAE(United States National Academy of Engineering)

    2015.6

  10. The Institue of Electrical Engineers of Japan

    2015.5

  11. 日本表面科学会   特別栄誉会員

    2015.5

  12. 日本物理学会   名誉会員

    2015.4

  13. The Institue of Electronics, Information and Communication Engineering

    2015.3

  14. 電子情報通信学会   名誉員

    2014.12

  15. Institute of Physics UK   Fellow

    2014.12

  16. Material Research Society   Regular Member

    2010.1

  17. 応用物理学会   名誉会員

    1984.10

  18. OSA

  19. SPIE

  20. Japan Society for Applied Physics

  21. Institute of Physics

  22. The Institue of Electrical Engineers of Japan

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  23. The Institue of Electronics, Information and Communication Engineering

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  24. 照明学会

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  25. 日本表面科学会

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  26. 日本物理学会

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  27. 日本工学アカデミー

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  28. 日本化学会

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  29. Japan Society for Applied Physics

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  30. SPIE

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  31. OSA

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  32. NAE(United States National Academy of Engineering)

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  33. Material Research Society

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  34. APS

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Committee Memberships 30

  1. IWUMD-2017   組織委員長  

    2016.10 - 2017.12   

  2. 国立研究会開発法人産業術総合研究所   柱冠フェロー  

    2016.8   

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    Committee type:Government

  3. International Solid State Lighting Alliance   国際諮問委員  

    2016.8   

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    Committee type:Academic society

  4. OPIC2017   組織委員  

    2016.8   

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    Committee type:Academic society

  5. 国際物理オリンピック日本大会   組織委員会副委員長  

    2016.5 - 2023.8   

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    Committee type:Other

  6. 日本結晶成長学会   評議員  

    2016.4 - 2019.3   

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    Committee type:Academic society

  7. 33rd International Conference on the Physics of Semiconductors国際諮問委員会   委員長  

    2015.9 - 2016.8   

  8. ・結晶成長の科学と技術第161委員会   委員  

    2015.8 - 2016.3   

  9. 2015 Rusnanoprize Award Committee   Member  

    2015.7   

  10. 2015 Rusnanoprize Award Committee   Member  

    2015.7   

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  11. 2015 Rusnanoprize Award Committee   Member  

    2015.7   

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  12. Optics & Photonics International Congress 2016組織委員会   委員  

    2015.7 - 2016.6   

  13. 江崎玲於奈賞委員会   委員  

    2015.6   

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    Committee type:Other

  14. 日本フォトニクス協議会 JPC関西   特別顧問  

    2015.5   

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    Committee type:Other

  15. 大阪大学光科学センター   特別顧問  

    2015.5 - 2017.9   

  16. ISPlasma2016/IC-PLANT2016組織委員会   委員長  

    2015.5 - 2016.4   

  17.   組織委員会委員     

    2014.7 - 2015.3   

  18. ISCS2014   Regional program chair  

    2013.4   

  19.   Program Committee Chair  

    2013.4 - 2014.3   

  20. OPIC2013   組織委員  

    2012.7   

  21. OPIC2013   組織委員  

    2012.7   

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  22. レーザ学会   専門委員会  

    2012.5 - 2015.3   

  23. 産業用LED応用研究会   委員長  

    2012.4   

  24.   プログラム委員会副委員長  

    2012.2 - 2012.4   

  25. 4th International Symposium on Growth of III-Nitrides   Program Committee Chair  

    2011.7 - 2012.7   

  26. ICMOVPE-XVI   International Advisory COmmittee  

    2011.6 - 2012.5   

  27. International Workshop on Nitride Semiconductors2012 (IWN2012)   Executive committee chair  

    2011.4 - 2012.10   

  28. 名古屋市科学館企画調査委員会   企画調査委員  

    2010.8   

  29. 電子部品・材料研究専門委員会   専門委員  

    2010.5 - 2012.5   

  30. ワイドギャップ半導体光・電子デバイス第162委員会   特別顧問  

    2010.4 - 2017.3   

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Awards 36

  1. 卓越教授

    2023.4   名古屋大学   卓越教授

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    Country:Japan

  2. 特別教授

    2019.10   広島大学   特別教授

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    Country:Japan

  3. 応用物理学会化合物半導体エレクトロニクス業績賞(赤﨑勇賞)

    2016.3   応用物理学会   青色及び紫外光デバイスの開発

    天野 浩

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    Award type:Award from Japanese society, conference, symposium, etc.  Country:Japan

  4. 丸八会顕彰

    2015.10   丸八会  

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    Country:Japan

  5. 第10回業績賞及び赤﨑勇賞

    2015.10   日本結晶成長学会   高品質窒化物半導体の創出と青色・紫外光素子の実現

    天野 浩

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    Award type:Award from Japanese society, conference, symposium, etc.  Country:Japan

  6. 2015 Asia Game Changers

    2015.10   Asia Society  

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    Award type:International academic award (Japan or overseas)  Country:United States

  7. 愛知県名誉県民

    2015.9   愛知県  

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    Country:Japan

  8. 産学官連携功労者表彰 日本学術会議会長賞,

    2015.8   日本学術会議会長   「短波長紫外LED」の開発

    天野 浩

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    Country:Japan

  9. 浜松市名誉市民

    2015.7   浜松市  

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    Country:Japan

  10. 中日文化賞

    2015.5   中日新聞  

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    Country:Japan

  11. 科学技術分野の文部科学大臣表彰 科学技術賞研究部門

    2015.4   文部科学大臣   

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    Country:Japan

  12. 特別教授

    2015.4   名古屋大学   特別教授

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    Country:Japan

  13. 特別栄誉教授

    2015.4   名城大学   特別栄誉教授

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    Country:Japan

  14. 日本スウェーデン協会 名誉会員

    2015.3   日本スウェーデン協会  

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    Country:Japan

  15. 電子情報通信学会 特別功績賞

    2015.3   電子情報通信学会  

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    Country:Japan

  16. 名古屋市学術表彰

    2015.1   名古屋市  

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    Country:Japan

  17. 愛知県学術顕彰

    2015.1   愛知県  

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    Country:Japan

  18. 静岡県民栄誉賞

    2015.1   静岡県  

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    Country:Japan

  19. ノーベル物理学賞

    2014.12   ノーベル財団  

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    Country:Sweden

  20. 文化功労者顕彰

    2014.11   文部科学大臣  

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    Country:Japan

  21. 文化勲章

    2014.11   首相  

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    Country:Japan

  22. APEX/JJAP Editorial Contribution Award

    2014.3   Japan Society of Applied Physics  

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    Country:Japan

  23. IOP Fellow

    2011.10   Institute of Physics  

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    Country:United Kingdom

  24. IOP Fellow

    2011.10   Institute of Physics   IOP Fellow

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    Country:United Kingdom

  25. ナイスステップな研究者2009

    2009.12   文部科学省 科学技術政策研究所  

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    Country:Japan

  26. ナイスステップな研究者2009

    2009.12   科学技術・政策研究所   青色及び紫外光デバイスの開発

    天野 浩

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    Country:Japan

  27. 応用物理学会フェロー

    2009.9   応用物理学会  

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    Country:Japan

  28. 日本結晶成長学会論文賞

    2008.11   日本結晶成長学会  

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    Country:Japan

  29. 第1回 P&I パテント・オブ・ザ・イヤー

    2004.11   東京工業大学精密工学研究所  

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    Country:Japan

  30. SSDM論文賞

    2003.9   SSDM  

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    Country:Japan

  31. 武田賞

    2002.11   竹田財団  

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    Country:Japan

  32. 丸文学術賞

    2001.3   丸文財団  

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    Country:Japan

  33. 英国Rank賞

    1998.12   Rank Foundation  

  34. 応用物理学会賞C(会誌賞)

    1998.9   応用物理学会  

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    Country:Japan

  35. IEEE/LEOS Engineering Achievement Award

    1996.11   IEEE/LEOS  

  36. Fifth Optoelectronics Conference A Special Award

    1994.7  

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Papers 832

  1. Observation of 2D-magnesium-intercalated gallium nitride superlattices.

    Wang J, Cai W, Lu W, Lu S, Kano E, Agulto VC, Sarkar B, Watanabe H, Ikarashi N, Iwamoto T, Nakajima M, Honda Y, Amano H

    Nature     2024.6

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Nature  

    Since the demonstration of p-type gallium nitride (GaN) through doping with substitutional magnesium (Mg) atoms1,2, rapid and comprehensive developments, such as blue light-emitting diodes, have considerably shaped our modern lives and contributed to a more carbon-neutral society3–5. However, the details of the interplay between GaN and Mg have remained largely unknown6–11. Here we observe that Mg-intercalated GaN superlattices can form spontaneously by annealing a metallic Mg film on GaN at atmospheric pressure. To our knowledge, this marks the first instance of a two-dimensional metal intercalated into a bulk semiconductor, with each Mg monolayer being intricately inserted between several monolayers of hexagonal GaN. Characterized as an interstitial intercalation, this process induces substantial uniaxial compressive strain perpendicular to the interstitial layers. Consequently, the GaN layers in the Mg-intercalated GaN superlattices exhibit an exceptional elastic strain exceeding −10% (equivalent to a stress of more than 20 GPa), among the highest recorded for thin-film materials12. The strain alters the electronic band structure and greatly enhances hole transport along the compression direction. Furthermore, the Mg sheets induce a unique periodic transition in GaN polarity, generating polarization-field-induced net charges. These characteristics offer fresh insights into semiconductor doping and conductivity enhancement, as well as into elastic strain engineering of nanomaterials and metal–semiconductor superlattices13.

    DOI: 10.1038/s41586-024-07513-x

    Scopus

    PubMed

  2. Recent advances in micro-pixel light emitting diode technology

    Park J.H., Pristovsek M., Amano H., Seong T.Y.

    Applied Physics Reviews   Vol. 11 ( 2 )   2024.6

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Applied Physics Reviews  

    Display technology has developed rapidly in recent years, with III-V system-based micro-light-emitting diodes (μLEDs) attracting attention as a means to overcome the physical limitations of current display systems related to their lifetime, brightness, contrast ratio, response time, and pixel size. However, for μLED displays to be successfully commercialized, their technical shortcomings need to be addressed. This review comprehensively discusses important issues associated with μLEDs, including the use of the ABC model for interpreting their behavior, size-dependent degradation mechanisms, methods for improving their efficiency, novel epitaxial structures, the development of red μLEDs, advanced transfer techniques for production, and the detection and repair of defects. Finally, industrial efforts to commercialize μLED displays are summarized. This review thus provides important insights into the potential realization of next-generation display systems based on μLEDs.

    DOI: 10.1063/5.0177550

    Scopus

  3. Impacts of vacancy complexes on the room-temperature photoluminescence lifetimes of state-of-the-art GaN substrates, epitaxial layers, and Mg-implanted layers

    Chichibu S.F., Shima K., Uedono A., Ishibashi S., Iguchi H., Narita T., Kataoka K., Tanaka R., Takashima S., Ueno K., Edo M., Watanabe H., Tanaka A., Honda Y., Suda J., Amano H., Kachi T., Nabatame T., Irokawa Y., Koide Y.

    Journal of Applied Physics   Vol. 135 ( 18 )   2024.5

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Journal of Applied Physics  

    For rooting the development of GaN-based optoelectronic devices, understanding the roles of midgap recombination centers (MGRCs), namely, nonradiative recombination centers and deep-state radiative recombination centers, on the carrier recombination dynamics is an essential task. By using the combination of time-resolved photoluminescence and positron annihilation spectroscopy (PAS) measurements, the origins of major MGRCs in the state-of-the-art GaN epilayers, bulk crystals, and Mg-implanted layers were identified, and their concentrations were quantified for deriving the capture coefficients of minority carriers. In this article, potential standardization of the room-temperature photoluminescence lifetime for the near-band-edge emission ( τ PL RT ) as the concentration of major MGRCs well below the detection limit of PAS is proposed. For n-GaN substrates and epilayers grown from the vapor phase, τ PL RT was limited by the concentration of carbon on N sites or divacancies comprising a Ga vacancy (VGa) and a N vacancy (VN), [VGaVN], when carbon concentration was higher or lower, respectively, than approximately 1016 cm−3. Here, carbon and VGaVN act as major deep-state radiative and nonradiative recombination centers, respectively, while major MGRCs in bulk GaN crystals were identified as VGa(VN)3 vacancy clusters in Na-flux GaN and VGa or VGaVN buried by a hydrogen and/or VGa decorated with oxygen on N sites, VGa(ON)3-4, in ammonothermal GaN. The values of τ PL RT in n-GaN samples are compared with those of p-GaN, in which τ PL RT was limited by the concentration of VGa(VN)2 in Mg-doped epilayers and by the concentrations of VGaVN and (VGaVN)3 in Mg-implanted GaN right after the implantation and after appropriate activation annealing, respectively.

    DOI: 10.1063/5.0201931

    Scopus

  4. Metastable atomic-ordered configurations for Al<sub>1/2</sub>Ga<sub>1/2</sub>N predicted by Monte-Carlo method based on first-principles calculations

    Gueriba, JS; Mizuseki, H; Cadatal-Raduban, M; Sarukura, N; Kawazoe, Y; Nagasawa, Y; Hirano, A; Amano, H

    JOURNAL OF PHYSICS-CONDENSED MATTER   Vol. 36 ( 13 )   2024.4

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Journal of Physics Condensed Matter  

    Metastability of Aln/12Ga1−n/12N (n = 2–10: integer) with the 1–2 monolayer (ML) in-plane configuration towards the c [0001] direction has been demonstrated recently. To theoretically explain the existence of these metastable structures, relatively large calculation cells are needed. However, previous calculations were limited to the use of small calculation cell sizes to estimate the local potential depth (∆σ) of ordered Al1/2Ga1/2N models. In this work, we were able to evaluate large calculation cells based on the interaction energies between proximate Al atoms (δEAl–Al) in AlGaN alloys. To do this, δEAl–Al values were estimated by first-principles calculations (FPCs) using a (5a1 × 5a2 × 5c) cell. Next, a survey of the possible ordered configurations using various large calculation cell models was performed using the estimated δEAl–Al values and the Monte-Carlo method. Then, various ∆σ values were estimated by FPCs and compared with the configurations previously reported by other research groups. We found that the ordered configuration obtained from the (4a1 × 2a2 × 1c) calculation cell (C42) has the lowest ∆σ of −9.3 meV/cation and exhibited an in-plane configuration at the c(0001) plane having (–Al–Al–Ga–Ga–) and (–Al–Ga–) sequence arrangements observed along the m{11̄00} planes. Hence, we found consistencies between the morphology obtained from experiment and the shape of the primitive cell based on our numerical calculations.

    DOI: 10.1088/1361-648X/ad1137

    Web of Science

    Scopus

    PubMed

  5. Investigation of carbon-related complexes in highly C-doped GaN grown by metalorganic vapor phase epitaxy

    Honda A., Watanabe H., Takeuchi W., Honda Y., Amano H., Kato T.

    Japanese Journal of Applied Physics   Vol. 63 ( 4 )   2024.4

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Japanese Journal of Applied Physics  

    We investigated the C-related complexes in highly C-doped GaN by electron spin resonance (ESR) spectroscopy, Fourier transform IR spectroscopy (FTIR), and minority carrier transient spectroscopy (MCTS) measurements. In the ESR spectra, two resonances with g values of 2.02 and 2.04 were found to be assigned by (0/−) deep acceptor and (+/0) charge transition levels of carbon substituting for nitrogen site (CN). In the FTIR spectra, two local vibrational modes positioned at 1679 and 1718 cm−1 were confirmed to be associated with tri-carbon complexes of CN-CGa-CN (basal) and CN-CGa-CN (axial), respectively. In the MCTS spectra, we observed the hole trap level of E v + 0.25 ± 0.1 eV associated with the tri-carbon complexes, which are the dominant C-related defects, suggesting that these complexes affect the electronic properties in the highly C-doped GaN.

    DOI: 10.35848/1347-4065/ad3b54

    Scopus

  6. Study on Degradation of Deep-Ultraviolet Laser Diode

    Zhang, ZY; Yoshikawa, A; Kushimoto, M; Sasaoka, C; Amano, H

    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE     2024.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Physica Status Solidi (A) Applications and Materials Science  

    The degradation of an AlGaN-based deep-ultraviolet laser diode during operation is studied. A rapid increase in threshold current without any facet mirror damage under direct current stress below the threshold current is observed, which is considered to limit the lifetime of continuous wave lasing to the level of seconds. The evolution of current–light and current–voltage characteristics suggests that the dominant mechanism of degradation is the increased loss of carriers before they can reach the active layer, i.e., the decrease in carrier injection efficiency. The decrease in emission intensity, which is more pronounced at lower current densities, and subsequent increase in sub-threshold current indicate the increase in defect density under current stress, which is similar to the well-analyzed degradation mechanism found in AlGaN-based light-emitting diodes.

    DOI: 10.1002/pssa.202300946

    Web of Science

    Scopus

  7. Impacts of off-angle and off-direction on surface morphology of GaN grown by metalorganic vapor phase epitaxy on (0001) GaN substrate

    Watanabe, H; Nitta, S; Ando, Y; Ohnishi, K; Honda, Y; Amano, H

    JOURNAL OF CRYSTAL GROWTH   Vol. 628   2024.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Journal of Crystal Growth  

    DOI: 10.1016/j.jcrysgro.2023.127552

    Web of Science

    Scopus

  8. Sn-doped n-type GaN layer with high electron density of 1020 cm-3 grown by halide vapor phase epitaxy

    Hamasaki, K; Ohnishi, K; Nitta, S; Fujimoto, N; Watanabe, H; Honda, Y; Amano, H

    JOURNAL OF CRYSTAL GROWTH   Vol. 628   2024.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Journal of Crystal Growth  

    A Sn-doped n-type GaN layer with a high electron density of 2 × 1020 cm−3 and a low resistivity of 8.7 × 10−4 Ω∙cm was grown by halide vapor phase epitaxy (HVPE). Sn doping was performed through the reaction between Sn metal and HCl gas. The Sn concentration markedly increased with decreasing growth temperature and the activation energy of Sn desorption from the GaN surface was found to be 4.1 eV. Smooth surfaces were obtained by introducing the Sn precursor even though the samples were grown at a low temperature of 905 °C, suggesting that Sn atoms act as surfactants and promote the migration of Ga adatoms. Almost all the Sn atoms act as donors in GaN below the Sn concentration of 2 × 1020 cm−3. These results indicate that using the Sn donor is promising for fabricating low-resistivity n-type GaN substrates by HVPE.

    DOI: 10.1016/j.jcrysgro.2023.127529

    Web of Science

    Scopus

  9. Impact of unintentionally formed compositionally graded layer on carrier injection efficiency in AlGaN-based deep-ultraviolet laser diodes

    Zhang Z., Yoshikawa A., Kushimoto M., Aoto K., Sasaoka C., Amano H.

    Applied Physics Letters   Vol. 124 ( 6 )   2024.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Applied Physics Letters  

    Increasing the injection efficiency, a critical factor constraining the reduction in threshold current in AlGaN-based deep-ultraviolet laser diodes, represents one of the paramount remaining technical challenges. In this study, the impact of compositionally graded layers that were unintentionally formed at the interface between the p-cladding and the core layer on carrier injection efficiency was analyzed. Experimental evaluations using laser diodes have shown that the elimination of an unintentionally formed layer increases the injection efficiency above the threshold current, from the conventional 3% to 13%. It has been postulated that the electron overflow toward the p-side exerts a substantial deleterious effect on the injection efficiency. An improvement in this aspect is achieved by increasing the electron-blocking capability due to the improved interface abruptness between the p-cladding layer and the core layer. The lasing threshold was strongly reduced, and characteristic temperature increased from 76 to 107 K for the improved devices.

    DOI: 10.1063/5.0184543

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  10. Optical activation of praseodymium ions implanted in gallium nitride after ultra-high pressure annealing

    Ito, S; Sato, S; Bockowski, M; Deki, M; Watanabe, H; Nitta, S; Honda, Y; Amano, H; Yoshida, K; Minagawa, H; Hagura, N

    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS   Vol. 547   2024.2

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    Lanthanide (Ln)-implanted gallium nitride (GaN) semiconductors have a variety of potential applications as light-emitting devices and quantum light sources, but their optical properties are not well understood. In this study, we investigate the room temperature optical properties of praseodymium (Pr) ion implanted single-crystal GaN and their changes upon ultrahigh pressure annealing (UHPA) up to 1480 °C. Photoluminescence (PL) spectra, luminescence transition lifetime, and excitation cross section of the implanted Pr ions are analyzed. In addition, the recovery of implantation-induced damage and the thermal diffusion of implanted Pr ions by UHPA are investigated by X-ray diffraction, Raman spectroscopy, and secondary ion mass spectrometry. The results show that the implantation damage is recovered by annealing at temperatures above 1200 °C, but Pr ions thermally diffuse to the surface as the annealing temperature increases. The annealing temperature at which a maximum PL intensity is obtained increases with increasing the implantation dose. However, the PL intensity decreases in all cases after annealing at 1480 °C, indicating that a quenching factor is dominant in this temperature range.

    DOI: 10.1016/j.nimb.2023.165181

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  11. Impurity reduction in lightly doped <i>n</i>-type gallium nitride layer grown via halogen-free vapor-phase epitaxy

    Kimura, T; Shimazu, H; Kataoka, K; Itoh, K; Narita, T; Uedono, A; Tokuda, Y; Tanaka, D; Nitta, S; Amano, H; Nakamura, D

    APPLIED PHYSICS LETTERS   Vol. 124 ( 5 )   2024.1

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    The development of gallium nitride (GaN) vertical-type metal-oxide-semiconductor field-effect transistors and p-i-n diode devices has gathered increasing attention. These devices require an n-type drift layer with a low doping level of 1016 cm−3 or less, minimized point defects inhibiting electron conduction, and a layer approximately 10 μm thick. Therefore, a practical method with a growth rate of at least several tens of μm/h and impurity concentrations of less than 1015 cm−3, except for that of dopants, is necessary. Halogen-free vapor-phase epitaxy (HF-VPE) has a high growth rate suitable for fabricating thick drift layers and utilizes a simple reaction between Ga vapor and ammonia gas (without a corrosive halogen gas), resulting in lower impurity levels. Herein, we eliminated the quartz content from the high-temperature zone to reduce the excess unintentional Si doping and identified that the nitrile gloves used for the growth preparation are other impurity contamination sources. We obtained a lightly n-type ([Si]=∼1016 cm−3) GaN layer, in which C, O, B, Fe, Mg, Al, Ca, Cr, Zn, Ni, Mn, and Ti impurity contents were below the detection limits of secondary ion mass spectrometry. Deep-level transient spectroscopy revealed that electron traps at EC − 0.26 and at EC − 0.59 eV were 2.7 × 1013 and 5.2 × 1014 cm−3, respectively. Moreover, the Hall effect analysis showed the acceptor-type defect-compensating donor content as approximately 2.7 × 1015 cm−3, resulting in a high electron mobility of HF-VPE GaN in the 30-710 K temperature range. Furthermore, we identified the Ca impurity as a deep acceptor, another killer defect leading to mobility collapse.

    DOI: 10.1063/5.0191774

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  12. Droop and light extraction of InGaN-based red micro-light-emitting diodes

    Park, JH; Pristovsek, M; Cai, WT; Kumabe, T; Choi, SY; Lee, DS; Seong, TY; Amano, H

    SEMICONDUCTOR SCIENCE AND TECHNOLOGY   Vol. 39 ( 1 )   2024.1

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    In this letter, we investigate the impact of periphery, width, length and area on the external quantum efficiency (EQE) of stripe-type InGaN-based red micro-light-emitting diodes (µLEDs). A longer periphery resulted in a higher light extraction efficiency ( η e ) via the sidewall regardless of the area of the µLEDs. However, as the injection current increased a somewhat larger efficiency droop was observed at the longer periphery due to current crowding. Additionally, larger µLEDs experienced more self-heating than smaller ones, resulting in a red shift of wavelengths and a larger efficiency droop. When the current density exceeded 100 A cm−2, the EQE ratio of smaller-area μLEDs to larger-area ones increased significantly due to the difference in efficiency droop. Besides, a short light propagation length and a long emission width yielded a higher η e . Hence, the periphery, width, length and area of the µLEDs determine EQE, which provides insight into the pixel design of µLED displays.

    DOI: 10.1088/1361-6641/ad0b88

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  13. Demonstration of AlGaN-on-AlN p-n Diodes With Dopant-Free Distributed Polarization Doping

    Kumabe T., Yoshikawa A., Kawasaki S., Kushimoto M., Honda Y., Arai M., Suda J., Amano H.

    IEEE Transactions on Electron Devices     2024

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    Nearly ideal vertical Al<inline-formula> <tex-math notation="LaTeX">$_{\textit{x}}$</tex-math> </inline-formula>Ga<inline-formula> <tex-math notation="LaTeX">$_{\text{1}-\textit{x}}$</tex-math> </inline-formula>N (<inline-formula> <tex-math notation="LaTeX">$\text{0.7} \leq \textit{x} &lt; \text{1.0}$</tex-math> </inline-formula>) p-n diodes are fabricated on an aluminum nitride (AlN) substrate. Distributed polarization doping (DPD) was employed for both p-type and n-type layers of the p-n junction, instead of conventional impurity doping, to overcome the major bottleneck of AlN-based material: the control of conductivity. Capacitance&#x2013;voltage measurements revealed that the net charge concentration agreed well with the DPD charge concentration expected from the device layer structure. The fabricated devices exhibited a low turn-on voltage of 6.5 V, a low differential specific ON-resistance of 3 M<inline-formula> <tex-math notation="LaTeX">$\Omega$</tex-math> </inline-formula> cm<inline-formula> <tex-math notation="LaTeX">$^{\text{2}}$</tex-math> </inline-formula>, electroluminescence (maximum at 5.1 eV), and an ideality factor of 2 for a wide range of temperatures (room temperature&#x2014;573 K). Moreover, the breakdown electric field was 7.3 MV cm<inline-formula> <tex-math notation="LaTeX">$^{-\text{1}}$</tex-math> </inline-formula>, which was almost twice as high as the reported critical electric field of GaN at the same doping concentration. These results clearly demonstrate the usefulness of DPD in the fabrication of high-performance AlN-based power devices.

    DOI: 10.1109/TED.2024.3367314

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  14. Temperature Dependence of α-Particle Detection Performance of GaN PIN Diode Detector

    Nakagawa, H; Hayashi, K; Miyazawa, A; Honda, Y; Amano, H; Aoki, T; Nakano, T

    SENSORS AND MATERIALS   Vol. 36 ( 1 ) page: 169 - 176   2024

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    Group-III nitride semiconductors, such as gallium nitride (GaN), have been proposed as novel materials for radiation detection owing to their wide bandgap and their ability to operate at high temperatures. In this study, the radiation detection properties of GaN PIN diode detectors were evaluated at high temperatures (~573 K). The energy spectrum peak profiles of241Am α-particles were obtained at different temperatures, confirming the operation of GaN PIN diodes up to 573 K. The peak positions shifted toward the lower-energy side and the full width at half maximum (FWHM) of the detection energy peak improved with increasing temperature. Furthermore, the variation in electron carrier mobility–lifetime product (μeτe) between 293 and 573 K was not significant. These results indicate the potential high-temperature operation of group-III nitride semiconductors. Additionally, the variation in each detection characteristic was caused by increasing the atmospheric temperature, which affected the mobility, lattice scattering, bandgap, and built-in potential differently.

    DOI: 10.18494/SAM4647

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  15. 15 GHz GaN Hi-Lo IMPATT Diodes With Pulsed Peak Power of 25.5 W

    Kawasaki, S; Kumabe, T; Deki, M; Watanabe, H; Tanaka, A; Honda, Y; Arai, M; Amano, H

    IEEE TRANSACTIONS ON ELECTRON DEVICES   Vol. 71 ( 3 ) page: 1408 - 1415   2023.12

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    The p+-n-n - n+ structure, known as Hi-Lo structure, was investigated in gallium nitride (GaN) single-drift-region (SDR) impact ionization avalanche transit-time (IMPATT) diodes to improve the output power and efficiency. The 15 GHz GaN Hi-Lo IMPATT diode was designed according to the Scharfetter and Gummel model under realistic conditions, suppressing the tunneling current (<10-4 cm2) and breakdown voltage (< 400 V). Even in such conditions, the calculated efficiency was higher than that of the p+-n abrupt junction structure and the improvement of RF characteristics was expected. The fabricated GaN Hi-Lo IMPATT diodes showed a clear avalanche breakdown and a pulsed microwave oscillation in the frequency range from 15 to 17 GHz. The maximum peak output power of 25.5 W and the efficiency of 2% were achieved, showing the highest values on microwave band GaN IMPATT diodes, and we confirmed that the Hi-Lo structure is effective for the high-power and high-efficiency operation of GaN IMPATT diodes.

    DOI: 10.1109/TED.2023.3345822

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  16. Anisotropic hole transport along [0001] and [1120] direction in p-doped (1010) GaN

    Lin, YY; Wang, J; Pristovsek, M; Honda, Y; Amano, H

    JOURNAL OF APPLIED PHYSICS   Vol. 134 ( 23 )   2023.12

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    The anisotropic hole transport along [0001] and [1120] in the p-doped (1010) GaN layer was compared for layers grown on bulk (1010) GaN substrates and on (1010) sapphire. The sheet resistance along [0001] was 1.1 times larger on GaN substrates and even 1.2 times larger on sapphire than that along [1120]. The anisotropic hole transport on bulk GaN substrates is due to the anisotropy of the hole’s effective mass and the different contribution of carriers in different bands, whereas the larger anisotropy for GaN on sapphire is also due to additional scattering at stacking faults. The annealing process of metal Mg applied to the m-plane p-type GaN successfully results in a robust p-type ohmic contact, functioning as a p++ layer.

    DOI: 10.1063/5.0177681

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  17. Improving the Barrier Height of N-Polar GaN Schottky Diodes Using Mg-Diffusion Process

    Sarkar, B; Wang, J; Watanabe, H; Amano, H

    IEEE TRANSACTIONS ON ELECTRON DEVICES   Vol. 71 ( 3 ) page: 1416 - 1420   2023.12

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    In this work, we report a low-cost methodology to increase the barrier height of N-polar GaN Schottky diodes. Physical vapor deposition (PVD) of Mg followed by a thermal diffusion anneal at 800 °C leads to the formation of N-polar GaN Camel diode offering a larger barrier height than the conventional N-polar GaN Schottky diodes. The increase in barrier height after the Mg diffusion process is validated using current-voltage ({I} - {V}) and capacitance-voltage (CV) measurements. A barrier height of 0.7 eV and a near-unity ideality factor observed in the N-polar GaN Camel diode confirms that the proposed Mg diffusion process is an alternative method for improving the performance of future N-polar GaN diodes.

    DOI: 10.1109/TED.2023.3341831

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  18. Electron lifetime and diffusion coefficient in dopant-free p-type distributed polarization doped AlGaN

    Kumabe, T; Kawasaki, S; Watanabe, H; Honda, Y; Amano, H

    APPLIED PHYSICS LETTERS   Vol. 123 ( 25 )   2023.12

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    Minority carrier properties in dopant-free p-type distributed polarization doped (DPD) AlGaN layers were investigated on the basis of the forward-biased current density-voltage (J-V) characteristics of p-n+ diodes. The fabricated p-DPD AlGaN/n+-AlGaN:Si diodes exhibited ideal electrical characteristics despite the absence of acceptor atoms in the p-type layer. The extracted Shockley-Read-Hall lifetime exceeded 300 ps, which was longer than that reported for p-GaN:Mg on GaN substrates with a similar acceptor concentration (20-50 ps). Moreover, the electron diffusion coefficient was about 20 cm2 s−1 at any temperature, which was convincing in terms of the electron mobility in DPD layers. The results suggest that p-DPD AlGaN has more desirable minority carrier properties than conventional p-GaN:Mg, particularly for bipolar device applications.

    DOI: 10.1063/5.0180062

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  19. Ga-polar GaN Camel diode enabled by a low-cost Mg-diffusion process

    Sarkar, B; Wang, J; Badami, O; Pramanik, T; Kwon, W; Watanabe, H; Amano, H

    APPLIED PHYSICS EXPRESS   Vol. 16 ( 12 )   2023.12

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    In this letter, we show that low-cost physical vapor deposition of Mg followed by a thermal diffusion annealing process increases the effective barrier height at the metal/Ga-polar GaN Schottky interface. Thus, for the first time, GaN Camel diodes with improved barrier height and turn-on voltage were realized compared to regular GaN Schottky barrier diodes. Temperature-dependent current-voltage characteristics indicated a near-homogeneous and near-ideal behavior of the GaN Camel diode. The analysis performed in this work is thought to be promising for improving the performance of future GaN-based unipolar diodes.

    DOI: 10.35848/1882-0786/ad0db9

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  20. Using low-temperature growth to resolve the composition pulling effect of UV-C LEDs

    Yoshikawa, A; Zhang, ZY; Kushimoto, M; Aoto, K; Sasaoka, C; Amano, H

    APPLIED PHYSICS LETTERS   Vol. 123 ( 22 )   2023.11

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    One approach to improving the output power of ultraviolet (UV-C) light-emitting diodes (LEDs) is to adopt an electron-blocking layer (EBL) with a high barrier. However, the intended effect may not be realized because of the composition pulling effect, which is the unintended occurrence of a gradient layer at an AlGaN/AlGaN hetero-interface with substantial differences in the Al composition. Here, we demonstrate that low-temperature growth (i.e., <1000 °C) can be used to control the unintentional gradient layer at an AlN/AlGaN hetero-interface between a barrier layer and AlN-EBL with a difference in Al compositions of more than 30%. LEDs with an emission wavelength of 265 nm were fabricated, and an AlN-EBL was grown at low temperature to realize an abrupt interface. At an applied current of 100 mA, growing the EBL under low-temperature conditions improved the forward voltage by 0.5 V and remarkably improved the peak luminous intensity by 1.4-1.6 times. Our results can be used to realize UV-C LEDs with a steep EBL and further improve their device characteristics.

    DOI: 10.1063/5.0183320

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  21. Multiplexing of bias-controlled modulation modes on a monolithic III-nitride optoelectronic chip

    Zhang, H; Ye, ZQ; Yan, JB; Shi, F; Shi, ZM; Li, DB; Liu, YH; Amano, H; Wang, YJ

    OPTICS LETTERS   Vol. 48 ( 19 ) page: 5069 - 5072   2023.10

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    III-nitride optoelectronic chips have tremendous potential for developing integrated computing and communication systems with low power consumption. The monolithic, top–down approaches are advantageous for simplifying the fabrication process and reducing the corresponding manufacturing cost. Herein, an ultraviolet optical interconnection system is investigated to discover the way of multiplexing between emission and absorption modulations on a monolithic optoelectronic chip. All on-chip components, the transmitter, monitor, waveguide, modulator, and receiver, share the same quantum well structure. As an example, two bias-controlled modulation modes are used to modulate video and audio signals in the experiment presented in this Letter. The results show that our on-chip optoelectronic system works efficiently in the near ultraviolet band, revealing the potential breadth of GaN optoelectronic integration.

    DOI: 10.1364/OL.503429

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  22. Dislocation Suppresses Sidewall-Surface Recombination of Micro-LEDs

    Park, JH; Pristovsek, M; Cai, WT; Cheong, HJ; Kang, CM; Lee, DS; Seong, TY; Amano, H

    LASER & PHOTONICS REVIEWS   Vol. 17 ( 10 )   2023.10

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    Nonradiative recombination rate that consists of dislocation-related nonradiative recombination rate (A0) and surface recombination rate (As) is one of the major parameters determining the performance of microlight-emitting diodes (µLEDs). Recent demonstrations improving the efficiency of blue InGaN or red AlGaInP µLEDs using specific methods such as atomic layer deposition or chemical treatment confirm the suppression of As. However, it is hardly found that those methods effectively improve the efficiency of red InGaN µLEDs so far. Here, it is discovered that the dislocation leads to an ineffective As. First, an intrinsic As degrades the external quantum efficiency (EQE) of blue InGaN µLEDs, resulting in EQE decreases with shrinking size. Second, panchromatic cathodoluminescence finds evidence that most of the carriers can be trapped before reaching the sidewall due to high A0. This results in shortened diffusion length of carriers and reduces the number of carriers reaching the sidewall. Consequently, the opposite trend of increasing EQE with shrinking size occurs in the case of red InGaN µLEDs due to an ineffective As. Furthermore, an 8.3 nm quantum well of InGaN with 13% Indium content that can reach a ≈690 nm wavelength at the low current is shown.

    DOI: 10.1002/lpor.202300199

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  23. UV/DUV light emitters

    Khan, A; Kneissl, M; Amano, H

    APPLIED PHYSICS LETTERS   Vol. 123 ( 12 )   2023.9

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    DOI: 10.1063/5.0174270

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  24. Impact of graphene state on the orientation of III-nitride

    Park, JH; Hu, N; Park, MD; Wang, J; Yang, X; Lee, DS; Amano, H; Pristovsek, M

    APPLIED PHYSICS LETTERS   Vol. 123 ( 12 )   2023.9

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    We attempted to grow (10-13) semi-polar GaN on graphene to confirm the possibility of a remote epitaxy of semi-polar GaN. Single crystalline (10-13) GaN was obtained on an optimized template using optimized growth conditions. However, (10-13), (0002), and other GaN orientations were found under the same growth conditions on a graphene-coated template. Scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy revealed that multi-domain GaN and (0002) GaN occurred in areas with a damaged graphene interfacial layer and intact graphene, respectively. Raman spectroscopy confirmed that graphene could survive under the growth conditions used here. Using cross-sectional scanning electron microscopy, we propose a simple approach to distinguish damaged graphene. Although the remote epitaxy of semi-polar GaN has not been demonstrated despite the usage of an optimized template and growth conditions, our results confirm the importance of the interfacial state in determining the crystallinity of the overgrown layer.

    DOI: 10.1063/5.0157588

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  25. Junction Diameter Dependence of Oscillation Frequency of GaN IMPATT Diode Up to 21 GHz

    Kawasaki, S; Kumabe, T; Ando, Y; Deki, M; Watanabe, H; Tanaka, A; Honda, Y; Arai, M; Amano, H

    IEEE ELECTRON DEVICE LETTERS   Vol. 44 ( 8 ) page: 1328 - 1331   2023.8

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    An experimental study on the effects of junction capacitance and current density on the oscillation characteristics of GaN single-drift-region (SDR) impact ionization avalanche transit-time (IMPATT) diodes were carried out using GaN p+-n abrupt junction diodes of various diameters, 200, 150, and 100 μ m , with a depletion layer width of 2 μ m. The fabricated diodes showed a clear avalanche breakdown at 315 V and a pulsed microwave oscillation with a peak output power exceeding 30 dBm. The oscillation frequency depended on junction diameter and current density. It was widely modulated from 8.56 to 21.1 GHz with decreasing junction diameter and increasing current density. The highest oscillation frequency was obtained with a current density of 13.8 kA/cm2 and a junction diameter of 100 μ m. A numerical calculation based on Read-type small-signal theory was carried out and found to well explain the experimental results.

    DOI: 10.1109/LED.2023.3285938

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  26. Investigation of Electrical Properties of N-Polar AlGaN/AlN Heterostructure Field-Effect Transistors

    Inahara, D; Matsuda, S; Matsumura, W; Okuno, R; Hanasaku, K; Kowaki, T; Miyamoto, M; Yao, YZ; Ishikawa, Y; Tanaka, A; Honda, Y; Nitta, S; Amano, H; Kurai, S; Okada, N; Yamada, Y

    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE   Vol. 220 ( 16 )   2023.8

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    AlN-based field-effect transistors (FETs) enable high-breakdown voltage, high drain current, and high-temperature operation. To realize high-frequency devices, N-polar AlGaN/AlN heterostructure FETs are focused on. N-polar Al0.1Ga0.9N/Al0.9Ga0.1N/AlN FET is fabricated using metal–organic vapor-phase epitaxy, and its electrical characteristics are evaluated. An N-polar AlN layer is grown on a sapphire substrate with a misorientation angle of 2.0° toward m-axis, on which a 20 nm thick Al0.9Ga0.1N base layer and a 20 nm Al0.1Ga0.9N channel layer are grown. The static FET operation is confirmed to exhibit an n-channel and pinch-off. Normally, during operation with a turn-on voltage of −3.2 V, a high operating breakdown voltage of 620 V and high operating temperature of 280 °C are also confirmed.

    DOI: 10.1002/pssa.202200871

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  27. Inactivation characteristics of a 280 nm Deep-UV irradiation dose on aerosolized SARS-CoV-2

    Takamure, K; Iwatani, Y; Amano, H; Yagi, T; Uchiyama, T

    ENVIRONMENT INTERNATIONAL   Vol. 177   page: 108022   2023.7

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    A non-filter virus inactivation unit was developed that can control the irradiation dose of aerosolized viruses by controlling the lighting pattern of a 280 nm deep-UV (DUV)-LED and the air flowrate. In this study, the inactivation properties of aerosolized SARS-CoV-2 were quantitatively evaluated by controlling the irradiation dose to the virus inside the inactivation unit. The RNA concentration of SARS-CoV-2 remained constant when the total irradiation dose of DUV irradiation to the virus exceeded 16.5 mJ/cm2. This observation suggests that RNA damage may occur in regions below the detection threshold of RT-qPCR assay. However, when the total irradiation dose was less than 16.5 mJ/cm2, the RNA concentration monotonically increased with a decreasing LED irradiation dose. However, the nucleocapsid protein concentration of SARS-CoV-2 was not predominantly dependent on the LED irradiation dose. The plaque assay showed that 99.16% of the virus was inactivated at 8.1 mJ/cm2 of irradiation, and no virus was detected at 12.2 mJ/cm2 of irradiation, resulting in a 99.89% virus inactivation rate. Thus, an irradiation dose of 23% of the maximal irradiation capacity of the virus inactivation unit can activate more than 99% of SARS-CoV-2. These findings are expected to enhance versatility in various applications. The downsizing achieved in our study renders the technology apt for installation in narrow spaces, while the enhanced flowrates establish its viability for implementation in larger facilities.

    DOI: 10.1016/j.envint.2023.108022

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  28. Reverse Leakage Mechanism of Dislocation-Free GaN Vertical p-n Diodes

    Kwon, W; Kawasaki, S; Watanabe, H; Tanaka, A; Honda, Y; Ikeda, H; Iso, K; Amano, H

    IEEE ELECTRON DEVICE LETTERS   Vol. 44 ( 7 ) page: 1172 - 1175   2023.7

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    The reverse leakage mechanism of threading dislocation (TD)-free gallium nitride (GaN) vertical p-n diode was investigated in various temperature range, and it was compared with that of the p-n diode having a threading dislocation density (TDD) of around 10^6 cm -2. The reverse leakage current was increased markedly by increasing the temperature from 400 K, the dominant mechanism was explained by thermionic and Poole-Frenkel emissions for TD-free and high-TDD p-n diodes, respectively. At high temperatures and electric fields, the leakage current of the high TDD p-n diode showed 2 times higher than the TD-free p-n diode. These results indicate that the performance of vertical GaN devices, especially when employed at high temperatures and electric fields, can be enhanced by removing TDs.

    DOI: 10.1109/LED.2023.3274306

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  29. Hole mobility limiting factors in dopant-free p-type distributed polarization-doped AlGaN

    Kumabe, T; Kawasaki, S; Watanabe, H; Honda, Y; Amano, H

    APPLIED PHYSICS LETTERS   Vol. 122 ( 25 )   2023.6

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    We investigated the hole mobility limiting factors in dopant-free p-type distributed polarization-doped (DPD) AlGaN layers by an experimental method. p-DPD AlGaN exhibited a higher hole mobility than GaN:Mg with a similar room temperature hole concentration across all temperature ranges owing to the absence of ionized impurity scattering. In addition, unlike in n-DPD AlGaN, alloy scattering was not always critical in p-DPD AlGaN. The extracted alloy scattering potential was only 0.3 eV, which resulted in a reduced effect of alloy scattering and originated from a small valence band offset in the GaN/AlN heterojunction system. The results suggest that DPD principally enables the fabrication of low-resistance p-type nitride semiconductor thin films as a result of the high hole concentration and high hole mobility.

    DOI: 10.1063/5.0155363

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  30. Stress relaxation of AlGaN on nonpolar m-plane GaN substrate

    Lin, YY; Sena, H; Frentrup, M; Pristovsek, M; Honda, Y; Amano, H

    JOURNAL OF APPLIED PHYSICS   Vol. 133 ( 22 )   2023.6

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    The stress relaxation with increasing thickness of metal-organic vapor phase epitaxy grown Al0.19Ga0.81N on quasi-bulk (101 ¯0) m-plane GaN substrates was investigated by x-ray diffraction. The anisotropic in-plane stress leads to an orthorhombic distortion of the lattice, which requires special mathematical treatment. Extending earlier works, we developed a method to calculate the distortion along [12 ¯10], [0001], and [101 ¯0] and obtained the lattice parameters, Al content, and strain values. The stress relaxation along the two in-plane directions involves two different mechanisms. First, the stress along [12 ¯10] relaxes by the onset of misfit dislocations through the { 10 1 ¯ 0 } ⟨ 1 2 ¯ 10 ⟩ slip system while for thicker layers the stress along [0001] relaxes by crack formation. Comparing the cathodoluminescence emission at room temperature with the expected bandgap showed that both tensile in-plane strains along [12 ¯10] and [0001] decrease the bandgap.

    DOI: 10.1063/5.0149838

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  31. Impact of Sidewall Conditions on Internal Quantum Efficiency and Light Extraction Efficiency of Micro-LEDs

    Park, JH; Pristovsek, M; Cai, WT; Cheong, HJ; Tanaka, A; Furusawa, Y; Han, DP; Seong, TY; Amano, H

    ADVANCED OPTICAL MATERIALS   Vol. 11 ( 10 )   2023.5

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    The sidewall condition is a key factor determining the performance of micro-light emitting diodes (µLEDs). In this study, equilateral triangular III-nitride blue µLEDs are prepared with exclusively m-plane sidewall surfaces to confirm the impact of sidewall conditions. It is found that inductively coupled plasma-reactive ion etching (ICP-RIE) causes surface damages to the sidewall and results in rough surface morphology. As confirmed by time-resolved photoluminescence (TRPL) and X-ray photoemission spectroscopy (XPS), tetramethylammonium hydroxide (TMAH) eliminates the etching damage and flattens the sidewall surface. After ICP-RIE, 100 µm2-µLEDs yield higher external quantum efficiency (EQE) than 400 µm2-µLEDs. However, after TMAH treatment, the peak EQE of 400 µm2-µLEDs increases by ≈10% in the low current regime, whereas that of 100 µm2-µLEDs slightly decreases by ≈3%. The EQE of the 100 µm2-µLEDs decreases after TMAH treatment although the internal quantum efficiency (IQE) increases. Further, the IQE of the 100 µm2-µLEDs before and after TMAH treatment is insignificant at temperatures below 150 K, above which it becomes considerable. Based on PL, XPS, scanning transmission electron microscopy, and scanning electron microscopy results, mechanisms for the size dependence of the EQE of µLEDs are explained in terms of non-radiative recombination rate and light extraction.

    DOI: 10.1002/adom.202203128

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  32. Lateral p-type GaN Schottky barrier diode with annealed Mg ohmic contact layer demonstrating ideal current-voltage characteristic

    Lu, S; Deki, M; Kumabe, T; Wang, J; Ohnishi, K; Watanabe, H; Nitta, S; Honda, Y; Amano, H

    APPLIED PHYSICS LETTERS   Vol. 122 ( 14 )   2023.4

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    We have demonstrated the fabrication process for a lateral p-type Schottky barrier diode (SBD) with the annealed Mg ohmic contact layer on a MOVPE-grown p-GaN wafer and measured the electrical characteristic of the diode. Because of the selective-area ohmic contact, the interface between the Schottky electrode and p-type GaN is well protected from any damage introduced by dry-etching or regrowth. The ideality factor of the forward current-voltage characteristic is as low as 1.09 at room temperature and an on-off ratio above 109 is also achieved. Various metals are deposited as the Schottky electrode and the work function dependence of the Schottky barrier height is confirmed with a pinning factor of 0.58. The temperature dependence of the current-voltage characteristic indicates that the GaN p-type SBD still fits the thermionic emission mode at 600 K with an ideality factor of 1.1. The reverse current of the p-SBD is also studied with the Poole-Frenkel emission model, and the trap energy level in the p-GaN is confirmed.

    DOI: 10.1063/5.0146080

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  33. Simultaneous light emission and detection of an AlGaInP quantum well diode

    Ye, ZQ; Zhang, H; Gao, XM; Fu, K; Zeng, HB; Liu, YH; Wang, YJ; Amano, H

    AIP ADVANCES   Vol. 13 ( 4 )   2023.4

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    When a quantum well (QW) diode is biased with a forward voltage and illuminated with an external shorter-wavelength light, the device simultaneously emits and detects light, with the injected current and the induced current mixed inside the wells. Separating these superimposed and dynamic electrical signals is useful for the development of multifunctional displays that can simultaneously transmit and receive light signals. By utilizing the unique overlap between the electroluminescence and detection spectra, we establish a wireless optical communication system using two AlGaInP diodes that have identical QW structures. The communication distance is 25 m, with one diode functioning as the transmitter and the other as the receiver. In particular, at the receiver end, the QW diode demonstrates simultaneous light emission and reception ability, and the mixed signals can be efficiently extracted, suggesting great potential for applications from light communication to advanced displays.

    DOI: 10.1063/5.0142093

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  34. 2D-GaN/AlN Multiple Quantum Disks/Quantum Well Heterostructures for High-Power Electron-Beam Pumped UVC Emitters.

    Jmerik V, Nechaev D, Semenov A, Evropeitsev E, Shubina T, Toropov A, Yagovkina M, Alekseev P, Borodin B, Orekhova K, Kozlovsky V, Zverev M, Gamov N, Wang T, Wang X, Pristovsek M, Amano H, Ivanov S

    Nanomaterials (Basel, Switzerland)   Vol. 13 ( 6 )   2023.3

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    DOI: 10.3390/nano13061077

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  35. A Review on the Progress of AlGaN Tunnel Homojunction Deep-Ultraviolet Light-Emitting Diodes

    Nagata, K; Matsubara, T; Saito, Y; Kataoka, K; Narita, T; Horibuchi, K; Kushimoto, M; Tomai, S; Katsumata, S; Honda, Y; Takeuchi, T; Amano, H

    CRYSTALS   Vol. 13 ( 3 )   2023.3

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    Conventional deep-ultraviolet (UV) light-emitting diodes (LEDs) based on AlGaN crystals have extremely low light-emission efficiencies due to the absorption in p-type GaN anode contacts. UV-light-transparent anode structures are considered as one of the solutions to increase a light output power. To this end, the present study focuses on developing a transparent AlGaN homoepitaxial tunnel junction (TJ) as the anode of a deep-UV LED. Deep-UV LEDs composed of n+/p+-type AlGaN TJs were fabricated under the growth condition that reduced the carrier compensation in the n+-type AlGaN layers. The developed deep-UV LED achieved an operating voltage of 10.8 V under a direct current (DC) operation of 63 A cm−2, which is one of the lowest values among devices composed of AlGaN tunnel homojunctions. In addition, magnesium zinc oxide (MgZnO)/Al reflective electrodes were fabricated to enhance the output power of the AlGaN homoepitaxial TJ LED. The output power was increased to 57.3 mW under a 63 A cm−2 DC operation, which was 1.7 times higher than that achieved using the conventional Ti/Al electrodes. The combination of the AlGaN-based TJ and MgZnO/Al reflective contact allows further improvement of the light output power. This study confirms that the AlGaN TJ is a promising UV-transmittance structure that can achieve a high light-extraction efficiency.

    DOI: 10.3390/cryst13030524

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  36. Temperature Field, Flow Field, and Temporal Fluctuations Thereof in Ammonothermal Growth of Bulk GaN-Transition from Dissolution Stage to Growth Stage Conditions.

    Schimmel S, Tomida D, Ishiguro T, Honda Y, Chichibu SF, Amano H

    Materials (Basel, Switzerland)   Vol. 16 ( 5 )   2023.2

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    With the ammonothermal method, one of the most promising technologies for scalable, cost-effective production of bulk single crystals of the wide bandgap semiconductor GaN is investigated. Specifically, etch-back and growth conditions, as well as the transition from the former to the latter, are studied using a 2D axis symmetrical numerical model. In addition, experimental crystal growth results are analyzed in terms of etch-back and crystal growth rates as a function of vertical seed position. The numerical results of internal process conditions are discussed. Variations along the vertical axis of the autoclave are analyzed using both numerical and experimental data. During the transition from quasi-stable conditions of the dissolution stage (etch-back process) to quasi-stable conditions of the growth stage, significant temperature differences of 20 K to 70 K (depending on vertical position) occur temporarily between the crystals and the surrounding fluid. These lead to maximum rates of seed temperature change of 2.5 K/min to 1.2 K/min depending on vertical position. Based on temperature differences between seeds, fluid, and autoclave wall upon the end of the set temperature inversion process, deposition of GaN is expected to be favored on the bottom seed. The temporarily observed differences between the mean temperature of each crystal and its fluid surrounding diminish about 2 h after reaching constant set temperatures imposed at the outer autoclave wall, whereas approximately quasi-stable conditions are reached about 3 h after reaching constant set temperatures. Short-term fluctuations in temperature are mostly due to fluctuations in velocity magnitude, usually with only minor variations in the flow direction.

    DOI: 10.3390/ma16052016

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  37. Red emission from InGaN active layer grown on nanoscale InGaN pseudosubstrates

    Cai, WT; Wang, J; Park, JH; Furusawa, Y; Cheong, HJ; Nitta, S; Honda, Y; Pristovsek, M; Amano, H

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 62 ( 2 )   2023.2

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    We demonstrated nanoplatelet In x Ga1−x N pseudosubstrates with In content varying from 0 to 0.3 on low-dislocation-density GaN substrates. These nanoplatelets efficiently relax in-plane strain, thus allowing for the use of a thick active layer to reduce built-in polarization. The 15 nm thick InGaN active layers grown under the same conditions on these nanoplatelets showed a remarkable cathodoluminescence redshift from 460 to 617 nm, suggesting enhanced In incorporation efficiency in InGaN nanoplatelets with higher In content. Moreover, the 617 nm-emitting sample presented an imperceptible blueshift under excitation-power-dependent photoluminescence, indicating a weak polarization field introduced by the high-In-content pseudosubstrates and the thick active layer.

    DOI: 10.35848/1347-4065/acb74c

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  38. Particle Collection Characteristics of Electrostatic Precipitator with Flat Plate Collection Electrodes

    TAKAMURE Kotaro, IWATANI Yasumasa, AMANO Hiroshi, YAGI Tetsuya, UCHIYAMA Tomomi

    The Proceedings of Mechanical Engineering Congress, Japan   Vol. 2023 ( 0 ) page: S054-05   2023

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    <p>An electrostatic precipitator suitable for the collection of aerosol-sized particles is developed. This device is a two-stage electrostatic precipitator divided into a corona discharge part and a collection electrode part. Positive ion is charged to the virus particles by corona discharge, and the negative pole of the collection electrode installed in the later stage collects these particles. The particle collection performance of the system is investigated when the inlet velocity (inlet flowrate) is varied. As a result, even at the same inlet velocity, the collection rate increased with smaller particle size. Furthermore, the collection efficiency of particles decreased with increasing flow velocity.</p>

    DOI: 10.1299/jsmemecj.2023.s054-05

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  39. Numerical simulation and validation of carbon incorporation in GaN epitaxial growth by MOVPE method

    MUKAIYAMA Yuji, WATANABE Hirotaka, NITTA Shugo, IIZUKA Masaya, AMANO Hiroshi

    The Proceedings of The Computational Mechanics Conference   Vol. 2023.36 ( 0 ) page: OS-1406   2023

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    <p>One of the crucial challenges in GaN epitaxial growth by metalorganic vapor phase epitaxy (MOVPE) method is the control of carbon (C) incorporation, which affects the resistivity of the individual layer of high-power and high-frequency devices based on GaN. Incorporating C into the GaN epilayer depends on various process parameters, such as growth temperature, pressure, carrier gas, flow rates of source gases, and reactor type. To determine the process parameters that control incorporated C concentration and uniformity, we have developed a novel numerical model for C incorporation into the grown GaN epilayer using MOVPE method. The developed model considers C incorporation through the decomposition of Ga source gas. We have implemented this model in a commercial crystal growth simulator, Virtual Reactor Nitride Edition, developed by STR. This study used experimental data to evaluate the dependence of temperature, growth rate, and V/III ratio of C incorporation predicted by the simulations. These results showed a strong correlation between the C concentration and these parameters, and good agreement with the experimental data.</p>

    DOI: 10.1299/jsmecmd.2023.36.os-1406

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  40. Metal Stop Laser Drilling for Blind via Holes of GaN-on-GaN Devices

    Sasaoka C., Ando Y., Takahashi H., Ikarashi N., Amano H.

    Physica Status Solidi (A) Applications and Materials Science     2023

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    The metal stop laser drilling of GaN-on-GaN devices is demonstrated using a UV sub-nanosecond laser as a light source. By monitoring the Bremsstrahlung emission at the drilling point, metal stops with a precision higher than 1 μm are realized for vias with a depth of 100 μm. From in situ laser-induced breakdown spectroscopy measurements, it is shown that endpoint detection is realized with high signal-to-noise ratio owing to the difference in the emission process between the strongly excited semiconductor and the metal. Herein, a through-substrate electrode with a resistance of less than 5 mΩ on GaN-on-GaN high-electron-mobility transistor (HEMT) wafers is demonstrated. The fabrication of through-substrate electrodes by this technique provides a simple process that does not require lithography or other complex processes. This process is expected to be useful in the fabrication of future GaN-on-GaN devices, including very thin GaN-on-GaN HEMTs.

    DOI: 10.1002/pssa.202200739

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  41. Photoelectron beam technology for SEM imaging with pixel-specific control of irradiation beam current

    Nishitani T., Arakawa Y., Noda S., Koizumi A., Sato D., Shikano H., Iijima H., Honda Y., Amano H.

    Proceedings of SPIE - The International Society for Optical Engineering   Vol. 12496   2023

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    The scanning electron microscope (SEM) with photocathode technology was launched by retrofitting the photocathode electron gun to a commercial-based SEM system. In this SEM system, the excitation laser for photoelectron generation from the photocathode is synchronized to the scanning signal. SEM images were obtained by high-speed modulation of the photoelectron beam current using the photocathode SEM, where the location in the field of view and its irradiation current were arbitrarily selected on a pixel-by-pixel basis (Selective e-Beaming technology). As a demonstration experiment contributing to non-contact electrical inspection, low-voltage SEM imaging of MOS-FET structures in 3D-NAND flash memory was performed using this selective e-beam technology. As a result, changes in the voltage contrast of the drain electrode were observed in response to on/off selective electron beam irradiation to the gate electrode in the MOS-FET structure. As an extension of the selective electron beaming technology, a Yield Controlled e-beaming (YCeB) technology was invented to control the secondary electron yield generated in the entire field of view of the SEM image by feedback control of the laser power irradiating the photocathode to the intensity of each pixel in the SEM image. The YCeB image, in which the laser power intensity corresponding to the probe intensity is modulated so that the secondary electron yield generated in the entire field of view of the SEM image is constant, is a clearer image with less noise than the original SEM image.

    DOI: 10.1117/12.2657853

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  42. Novel Electron Beam Technology using InGaN Photocathode for High-Throughput Scanning Electron Microscope Imaging

    Sato, D; Koizumi, A; Shikano, H; Noda, S; Otsuka, Y; Yasufuku, D; Mori, K; Iijima, H; Nishitani, T; Honda, Y; Amano, H

    METROLOGY, INSPECTION, AND PROCESS CONTROL XXXVII   Vol. 12496   2023

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    An InGaN photocathode with a negative electron affinity (NEA) surface is suitable for industrial use because of features such as a long quantum efficiency lifetime, availability with a visible laser as an excitation light source, and the presence of a transmission-type structure. The first objective is the development of an InGaN photocathode electron gun that can be mounted on a scanning electron microscope (SEM) and the evaluation of the electron beam size at the emission point, maximum emission current, and transverse energy of the electron beam, which are important factors for realizing a high probe current in the SEM. The second objective is the evaluation of emission current stability, while the third objective is the generation of a pulsed electron beam and multi-electron beam from the InGaN photocathode. The parameters of the electron beam from the photocathode electron gun were an emission beam radius of 1 µm, transverse energy of 44 meV, and an emission current of up to 110 µA. Using a high beam current with low transverse energy from the photocathode, a 13 nA probe current with 10 nm SEM resolution was observed with 15 µA emission. At 15 µA, the continuous electron beam emission for 1300 h was confirmed; at 30 µA, the cycle time between the NEA surface reactivations was confirmed to be 90 h with 0.043% stability. Moreover, a 4.4 ns pulsed e-beam with a 4.7 mA beam current was generated, and a 5 × 5 multielectron beam with 12% uniformity was then obtained. The advantages of the InGaN photocathode, such as high electron beam current, low transverse energy, long quantum efficiency lifetime, pulsed electron beam, and multi-electron beam, are useful in industries including semiconductor device inspection tools.

    DOI: 10.1117/12.2657032

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  43. Challenges and opportunities of nitride light emitting devices by HVPE thanks to a stable Mg source

    Matsumoto K., Ohnishi K., Amano H.

    Proceedings of SPIE - The International Society for Optical Engineering   Vol. 12441   2023

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    Until recently, lack of stable p-type doping source in HVPE hindered its use to the application of III-nitride light emitting devices. Recently, K. Ohnishi discovered the stable MgO source for p-type doping in GaN HVPE. This has enabled the use of HVPE for light emitting devices as well as electron devices such as vertical MOSFET. In this article, we will review the current HVPE technology of p-GaN HVPE, multi-junction AlInGaP/InGaP/GaAs solar cell, InGaN HVPE by tri-chlorides, and discuss the challenge and opportunities of III-nitride HVPE in terms of epitaxial layer design and the remaining issues of the growth of the low temperature buffer, MQWs as well as the source supply design to grow multilayer structures.

    DOI: 10.1117/12.2647336

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  44. Development in AlGaN homojunction tunnel junction deep UV LEDs

    Nagata K., Anada S., Saito Y., Kushimoto M., Honda Y., Takeuchi T., Amano H.

    Proceedings of SPIE - The International Society for Optical Engineering   Vol. 12441   2023

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    To reduce the operating voltage, we analyzed the p-n junction of an aluminum gallium nitride (AlGaN) homojunction tunnel junction (TJ) deep-ultraviolet light-emitting diode using phase-shifting electron holography. We obtained a phase image reflecting the band alignment of the p-n homojunction and derived a depletion layer width of approximately 10 nm. We found the AlGaN homojunction TJ forms a p-n junction. Furthermore, the operating voltage reached 8.8 V at 63 A cm-2 by optimizing the structural characteristics of the AlGaN TJ, such as the thickness and impurity concentration, where the thickness of the TJ was 23 nm. We found that the TJ thickness should be at least the same as the depletion layer width at the AlGaN TJ.

    DOI: 10.1117/12.2646757

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  45. Demonstration of AlN-based Vertical p-n Diodes with Dopant-Free Distributed-Polarization Doping

    Kumabe T., Yoshikawa A., Kushimoto M., Honda Y., Arai M., Suda J., Amano H.

    Technical Digest - International Electron Devices Meeting, IEDM     2023

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    Nearly ideal AlN-based vertical p-n diodes are demonstrated on an AIN substrate utilizing dopant-free distributed-polarization doping (DPD). Capacitance-voltage measurements revealed that the effective doping concentration agreed well with the designed DPD charge concentration. The fabricated devices exhibited a low tum-on voltage of 6.5 V, a low differential specific ON-resistance of 3 mO cm2, and an ideality factor of 2 for a wide range of temperatures (room temperature-573 K). Moreover, the breakdown electric field was 7.3 MV/cm, which was almost twice as high as the reported critical electric field of 4H-SÌC and GaN. These results clearly demonstrate the usefulness of DPD in the fabrication of high-performance AlN-based power devices.

    DOI: 10.1109/IEDM45741.2023.10413866

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  46. Photon extraction enhancement of praseodymium ions in gallium nitride nanopillars

    Sato, SI; Li, S; Greentree, AD; Deki, M; Nishimura, T; Watanabe, H; Nitta, S; Honda, Y; Amano, H; Gibson, BC; Ohshima, T

    SCIENTIFIC REPORTS   Vol. 12 ( 1 ) page: 21208   2022.12

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    Lanthanoid-doped Gallium Nitride (GaN) integrated into nanophotonic technologies is a promising candidate for room-temperature quantum photon sources for quantum technology applications. We manufactured praseodymium (Pr)-doped GaN nanopillars of varying size, and showed significantly enhanced room-temperature photon extraction efficiency compared to unstructured Pr-doped GaN. Implanted Pr ions in GaN show two main emission peaks at 650.3 nm and 651.8 nm which are attributed to 3P0-3F2 transition in the 4f-shell. The maximum observed enhancement ratio was 23.5 for 200 nm diameter circular pillars, which can be divided into the emitted photon extraction enhancement by a factor of 4.5 and the photon collection enhancement by a factor of 5.2. The enhancement mechanism is explained by the eigenmode resonance inside the nanopillar. Our study provides a pathway for Lanthanoid-doped GaN nano/micro-scale photon emitters and quantum technology applications.

    DOI: 10.1038/s41598-022-25522-6

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  47. Characteristics of collection and inactivation of virus in air flowing inside a winding conduit equipped with 280 nm deep UV-LEDs

    Takamure, K; Sakamoto, Y; Iwatani, Y; Amano, H; Yagi, T; Uchiyama, T

    ENVIRONMENT INTERNATIONAL   Vol. 170   page: 107580   2022.12

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    A general-purpose virus inactivation unit that can inactivate viruses was developed using deep ultraviolet (DUV) LEDs that emit DUV rays with a wavelength of 280 nm. The inside of the virus inactivation unit is a rectangular conduit with a sharp turn of 180° (sharp-turned rectangular conduit). Virus inactivation is attempted by directly irradiating the air passing through the conduit with DUV rays. The flow characteristics of air and virus particles inside the virus inactivation unit were investigated using numerical simulations. The air was locally accelerated at the sharp turn parts and flowed along the partition plate in the sharp-turned rectangular conduit. The aerosol particles moving in the sharp-turned rectangular conduit were greatly bent in orbit at the sharp turn parts, and then rapidly approached the partition plate at the lower part of the conduit. Consequently, many particles collided with the partition plates behind the sharp-turn parts. SARS-CoV-2 virus was nebulized in the virus inactivation unit, and the RNA concentration and virus inactivation rate with and without the emission of DUV-LEDs were measured in the experiment. The concentration of SARS-CoV-2 RNA was reduced to 60% through DUV-LED irradiation. In addition, SARS-CoV-2 passing through the virus inactivation unit was inactivated below the detection limit by the emission of DUV-LEDs. The virus inactivation rate and the value of the detection limit corresponded to 99.38% and 35.36 TCID50/mL, respectively.

    DOI: 10.1016/j.envint.2022.107580

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  48. Scanning electron microscope imaging by selective e-beaming using photoelectron beams from semiconductor photocathodes

    Nishitani, T; Arakawa, Y; Noda, S; Koizumi, A; Sato, D; Shikano, H; Iijima, H; Honda, Y; Amano, H

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B   Vol. 40 ( 6 )   2022.12

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    Pulsed electron beams from a photocathode using an InGaN semiconductor have brought selectively scanning technology to scanning electron microscopes, where the electron beam irradiation intensity and area can be arbitrarily selected within the field of view in SEM images. The p-type InGaN semiconductor crystals grown in the metalorganic chemical vapor deposition equipment were used as the photocathode material for the electron beam source after the surface was activated to a negative electron affinity state in the electron gun under ultrahigh vacuum. The InGaN semiconductor photocathode produced a pulsed electron beam with a rise and fall time of 3 ns, consistent with the time structure of the irradiated pulsed laser used for the optical excitation of electrons. The InGaN photocathode-based electron gun achieved a total beam operation time of 1300 h at 15 μA beam current with a downtime rate of 4% and a current stability of 0.033% after 23 cycles of surface activation and continuous beam operation. The InGaN photocathode-based electron gun has been installed in the conventional scanning electron microscope by replacing the original field emission gun. SEM imaging was performed by selective electron beaming, in which the scanning signal of the SEM system was synchronized with the laser for photocathode excitation to irradiate arbitrary regions in the SEM image at arbitrary intensity. The accuracy of the selection of regions in the SEM image by the selective electron beam was pixel by pixel at the TV scan speed (80 ns/pix, 25 frame/s) of the SEM.

    DOI: 10.1116/6.0002111

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  49. Key temperature-dependent characteristics of AlGaN-based UV-C laser diode and demonstration of room-temperature continuous-wave lasing

    Zhang, ZY; Kushimoto, M; Yoshikawa, A; Aoto, K; Sasaoka, C; Schowalter, LJ; Amano, H

    APPLIED PHYSICS LETTERS   Vol. 121 ( 22 )   2022.11

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    Although the pulsed operation of AlGaN-based laser diodes at UV-C wavelengths has been confirmed in the previous studies, continuous oscillation without cooling is difficult because of the high operating voltage. In this study, the temperature dependence of key parameters was investigated and their impact on achieving continuous-wave lasing was discussed. A reduction in the threshold voltage was achieved by tapering the sides of the laser diode mesa and reducing the lateral distance between the n- and p-electrodes. As a result, continuous-wave lasing at room temperature was demonstrated at a threshold current density of 4.2 kA / cm 2 and a threshold voltage of 8.7 V.

    DOI: 10.1063/5.0124480

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  50. Local stress control to suppress dislocation generation for pseudomorphically grown AlGaN UV-C laser diodes

    Kushimoto, M; Zhang, ZY; Yoshikawa, A; Aoto, K; Honda, Y; Sasaoka, C; Schowalter, LJ; Amano, H

    APPLIED PHYSICS LETTERS   Vol. 121 ( 22 )   2022.11

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    Previously reported UV-C laser diode (LD) structures have been subject to design constraints owing to dark line defects at the edge of the mesa stripe after device fabrication. To address this issue, a detailed analysis revealed that the dark line defects were dislocations generated by local residual shear stresses associated with mesa formation on highly strained epitaxial layers. A technique for controlling the local concentration of shear stress using a sloped mesa geometry was proposed based on insight gained by modeling the stress distribution at the edge of the mesa stripe. Experimental results showed that this technique succeeded in completely suppressing the emergence of dark-line defects. This technique will be useful in improving the performance of pseudomorphic AlGaN/AlN-based optoelectronic devices, including UV-C LDs.

    DOI: 10.1063/5.0124512

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  51. High In content nitride sub-micrometer platelet arrays for long wavelength optical applications

    Cai, WT; Furusawa, Y; Wang, J; Park, JH; Liao, YQ; Cheong, HJ; Nitta, S; Honda, Y; Pristovsek, M; Amano, H

    APPLIED PHYSICS LETTERS   Vol. 121 ( 21 )   2022.11

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    We demonstrate high, up to 30% In content InGaN sub-micrometer platelets on GaN by metalorganic vapor phase epitaxy. These InGaN platelets were selectively grown on flat GaN seeds formed in sub-micrometer-scale openings in a SiNx mask. The platelets were highly uniform without any dislocations or pits, with an atomically flat (0001) surface. The typical height was ∼120 nm, which significantly exceeded the normal critical layer thickness of a c-plane InGaN film. The strain state was comprehensively characterized by microbeam x-ray diffraction and transmission electron microscopy. Due to a gradual elastic relaxation of strain, the In content increased almost linearly from bottom to top because of the strong strain-dependent In incorporation. These platelets can serve as high-quality strain-relaxed templates for long wavelength micro-light-emitting diodes.

    DOI: 10.1063/5.0120723

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  52. Electrical Characteristics of Thermally Stable Ag-Pd-Cu Alloy Schottky Contacts on <i>n-</i>Al<sub>0.6</sub>Ga<sub>0.4</sub>N

    Sim, KB; Kim, SK; Seong, TY; Amano, H

    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY   Vol. 11 ( 11 )   2022.11

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    We report the fabrication of high-barrier-height and thermally reliable Schottky contacts to n-Al0.6Ga0.4N by using an Ag-Pd-Cu (APC) alloy. The Schottky barrier heights (SBHs) and ideality factors computed using the current-voltage (I-V) model ranged from 0.82 to 0.97 eV and from 3.15 to 3.44, respectively. The barrier inhomogeneity model and capacitance-voltage (C-V) method yielded higher SBHs (1.62-2.19 eV) than those obtained using the I-V model. The 300 °C-annealed APC sample exhibited more uniform electrical characteristics than the 500 °C-annealed Ni/Au Schottky samples (each with the best Schottky behavior). Furthermore, the scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) results indicated that the APC Schottky contacts were more thermally stable than the Ni/Au contacts. On the basis of the X-ray photoemission spectroscopy (XPS) results, the improved Schottky characteristics of the APC alloy contacts are described and discussed.

    DOI: 10.1149/2162-8777/aca1df

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  53. Substitutional diffusion of Mg into GaN from GaN/Mg mixture

    Itoh, Y; Lu, S; Watanabe, H; Deki, M; Nitta, S; Honda, Y; Tanaka, A; Amano, H

    APPLIED PHYSICS EXPRESS   Vol. 15 ( 11 )   2022.11

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    We evaluated Mg-diffusion into GaN from GaN/Mg mixture. The diffusion depth of Mg increased with diffusion temperature from 1100 °C to 1300 °C, whereas the Mg concentration remained constant at 2-3 × 1018 cm−3 independent of temperature. The estimated activation energy for Mg diffusion was 2.8 eV, from which the substitutional diffusion mechanism was predicted. Mg-diffused GaN samples showed p-type conductivity with a maximum hole mobility of 27.7 cm2 V−1 s−1, suggesting that substitutional diffusion contributes to Mg activation. This diffusion technique can be used to easily form p-type GaN and has potential as a p-type selective doping technique.

    DOI: 10.35848/1882-0786/ac9c83

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  54. Adsorption structure deteriorating negative electron affinity under the H<sub>2</sub>O environment

    Kashima, M; Ishiyama, S; Sato, D; Koizumi, A; Iijima, H; Nishitani, T; Honda, Y; Amano, H; Meguro, T

    APPLIED PHYSICS LETTERS   Vol. 121 ( 18 )   2022.10

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    Photocathodes with negative electron affinity (NEA) characteristics have various advantages, such as small energy spread, high spin polarization, and ultrashort pulsing. Nitride semiconductors, such as GaN and InGaN, are promising materials for NEA photocathodes because their lifetimes are longer than those of other materials. In order to further prolong the lifetime, it is important to better understand the deterioration of NEA characteristics. The adsorption of residual gases and back-bombardment by ionized residual gases shorten the lifetime. Among the adsorbed residual gases, H2O has a significant influence. However, the adsorption structures produced by the reaction with H2O are not comprehensively studied so far. In this study, we investigated adsorption structures that deteriorated the NEA characteristics by exposing InGaN and GaAs to an H2O environment and discussed the differences in their lifetimes. By comparing the temperature-programmed desorption curves with and without H2O exposure, the generation of CsOH was confirmed. The desorption of CsOH demonstrated different photoemission behaviors between InGaN and GaAs results. InGaN recovered its NEA characteristics, whereas GaAs did not. Considering the Cs desorption spectra, it is difficult for an NEA surface on InGaN to change chemically, whereas that for GaAs changes easily. The chemical reactivity of the NEA surface is different for InGaN and GaAs, which contributes to the duration of photoemission. We have attempted to prolong the lifetime of InGaN by recovering its NEA characteristics. We found that InGaN with NEA characteristics can be reused easily without thermal treatment at high temperatures.

    DOI: 10.1063/5.0125344

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  55. Monolithic GaN optoelectronic system on a Si substrate

    Zhang, H; Yan, JB; Ye, ZQ; Shi, F; Piao, JL; Wang, W; Gao, XM; Zhu, HB; Wang, YJ; Liu, YH; Amano, H

    APPLIED PHYSICS LETTERS   Vol. 121 ( 18 )   2022.10

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    GaN-based devices have grown rapidly in recent decades, due to their important research value and application prospects. There is a desire to monolithically integrate different GaN devices into a single chip for the development of future optoelectronic systems with low power consumption. In addition to improved multifunctional performance, a miniature integrated system can result in a significant reduction in material costs, processing costs, and packaging costs. In view of such prospects, we propose monolithic, top-down approaches to build III-nitride transmitter, modulator, waveguide, beam splitter, receiver, and monitor as a single unit onto a conventional GaN-on-silicon wafer without involving regrowth or postgrowth doping. Data communication among these components is realized through light propagation, opening up horizons for GaN optoelectronic systems on a chip.

    DOI: 10.1063/5.0125324

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  56. The photoemission characteristics of a NEA InGaN photocathode by simultaneously supplying Cs and O2

    Kashima, M; Itokawa, Y; Kanai, T; Sato, D; Koizumi, A; Iijima, H; Nishitani, T; Honda, Y; Amano, H; Meguro, T

    APPLIED SURFACE SCIENCE   Vol. 599   2022.10

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    A high quantum efficiency (QE) can be obtained on negative electron affinity (NEA) surfaces. It is well-known that NEA surfaces can be formed on semiconductor materials such as GaAs by the alternating supply of cesium (Cs) and oxygen (O2), which is called the yo-yo method. While GaN and related compounds such as InGaN are expected to realize an NEA photocathode with a long lifetime, the surface reactions between GaAs and nitride semiconductors are completely different with respect to the increasing rate of QE induced by the supply of O2. In addition, the surface processes of photoemission from NEA nitride semiconductors have not yet been elucidated. In the present study, a higher QE was achieved in InGaN by simultaneously supplying Cs and O2 instead of using the conventional yo-yo method. The possible Cs adsorption states in relation to the photoemission are also discussed based on the QE tendencies and the temperature programmed desorption (TPD) spectra of the NEA surfaces formed under elevated temperature conditions. This study suggests that the Cs oxide species, which is one of the key compounds for imparting the NEA nature, decomposes at approximately 350 °C and that the InGaN-Cs2O2 structure is a possible candidate for NEA photocathodes.

    DOI: 10.1016/j.apsusc.2022.153882

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  57. Tuning the p-type doping of GaN over three orders of magnitude via efficient Mg doping during halide vapor phase epitaxy

    Ohnishi, K; Fujimoto, N; Nitta, S; Watanabe, H; Lu, S; Deki, M; Honda, Y; Amano, H

    JOURNAL OF APPLIED PHYSICS   Vol. 132 ( 14 )   2022.10

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    The precise control of Mg concentration ([Mg]) in p-type GaN layers from 2.3 × 1016 to 2.0 × 1019 cm-3 was demonstrated by halide vapor phase epitaxy (HVPE) on n-type GaN (0001) freestanding substrates. [Mg] in GaN layers could be controlled well by varying the input partial pressure of MgCl2 formed by a chemical reaction between MgO solid and HCl gas under the thermodynamic equilibrium condition. In the sample with [Mg] of 2.0 × 1019 cm-3, a step-bunched surface was observed because the surface migration of Ga adatoms was enhanced by the surfactant effect of Mg atoms. The samples show high structural qualities determined from x-ray rocking curve measurements. The acceptor concentration was in good agreement with [Mg], indicating that almost all Mg atoms act as acceptors. The compensating donor concentrations in the samples were higher than the concentrations of Si, O, and C impurities. We also obtained the Mg acceptor level at a sufficiently low net acceptor concentration of 245 ± 2 meV. These results show that the HVPE method is promising for fabricating GaN vertical power devices, such as n-channel metal-oxide-semiconductor field-effect transistors.

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  58. High-Energy Computed Tomography as a Prospective Tool for In Situ Monitoring of Mass Transfer Processes inside High-Pressure Reactors-A Case Study on Ammonothermal Bulk Crystal Growth of Nitrides including GaN

    Schimmel, S; Salamon, M; Tomida, D; Neumeier, S; Ishiguro, T; Honda, Y; Chichibu, SF; Amano, H

    MATERIALS   Vol. 15 ( 17 )   2022.9

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    For the fundamental understanding and the technological development of the ammonothermal method for the synthesis and crystal growth of nitrides, an in situ monitoring technique for tracking mass transport of the nitride throughout the entire autoclave volume is desirable. The feasibility of using high-energy computed tomography for this purpose was therefore evaluated using ex situ measurements. Acceleration voltages of 600 kV were estimated to yield suitable transparency in a lab-scale ammonothermal setup for GaN crystal growth designed for up to 300 MPa operating pressure. The total scan duration was estimated to be in the order of 20 to 40 min, which was sufficient given the comparatively slow crystal growth speed in ammonothermal growth. Even shorter scan durations or, alternatively, lower acceleration voltages for improved contrast or reduced X-ray shielding requirements, were estimated to be feasible in the case of ammonoacidic growth, as the lower pressure requirements for this process variant allow for thinned autoclave walls in an adapted setup designed for improved X-ray transparency. Promising nickel-base and cobalt-base alloys for applications in ammonothermal reactors with reduced X-ray absorption in relation to the maximum operating pressure were identified. The applicability for the validation of numerical simulations of the growth process of GaN, in addition to the applicability of the technique to further nitride materials, as well as larger reactors and bulk crystals, were evaluated.

    DOI: 10.3390/ma15176165

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  59. Understanding indium incorporation of InGaN grown on polar, semi-polar, and non-polar orientation by metal-organic vapor phase epitaxy

    Hu, N; Avit, G; Pristovsek, M; Honda, Y; Amano, H

    APPLIED PHYSICS LETTERS   Vol. 121 ( 8 )   2022.8

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    We studied indium incorporation into InGaN/GaN quantum wells grown by metal-organic vapor phase epitaxy by systematically varying of gallium and indium precursor flows on (0001), (10 1 ¯3), (11 2 ¯2), and (10 1 ¯0) orientations. The layer thickness and indium composition obtained from x-ray diffraction analysis were correlated with a model based on indium and gallium incorporation efficiencies. In the model, the indium incorporation efficiency is reproduced by the Langmuir surface coverage of gallium, indicating that indium atoms close to gallium atoms can be incorporated preferably.

    DOI: 10.1063/5.0088908

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  60. Surface kinetics in halide vapor phase epitaxial growth of GaN layers on GaN (0001) freestanding substrates

    Ohnishi, K; Fujimoto, N; Nitta, S; Watanabe, H; Honda, Y; Amano, H

    JOURNAL OF CRYSTAL GROWTH   Vol. 592   2022.8

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    The effects of halide vapor phase epitaxial (HVPE) growth conditions such as input V/III ratio and substrate off-cut angle on the surface morphology of n-type GaN layers grown on GaN (0001) freestanding substrates were investigated to develop a model for growing smooth surfaces. The spiral hillock density increased with increasing input V/III ratio and/or decreasing off-cut angle. The critical off-cut angle between the spiral growth and the step-flow growth depended on the vapor supersaturation calculated by thermodynamic analysis. To understand the transition of the growth mode, we proposed a Burton–Cabrera–Frank-theory-based model considering the effect of spiral growth, which was utilized to explain the obtained experimental results. The developed growth model can be effective for predicting the HVPE growth mode between the spiral growth and the step-flow growth.

    DOI: 10.1016/j.jcrysgro.2022.126749

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  61. Improved performance of deep ultraviolet AlGaN-based light-emitting diode by reducing contact resistance of Al-based reflector

    Sim K.B., Jin J.Y., Kim S.K., Ko Y.J., Hwang G.W., Seong T.Y., Amano H.

    Journal of Alloys and Compounds   Vol. 910   2022.7

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    In this study, chlorine (Cl) treatment was carried out on p-AlGaN to enhance the performance of ultraviolet-C light emitting diodes (UVC LEDs) by modifying ITO work function and hence reducing the contact resistance of ITO/Al reflector. The Cl-treated UVC LEDs exhibit the forward voltage of 6.88 V at 20 mA, whereas the reference samples show 7.50 V. The light output power and relative wall plug efficiency (WPE) of the Cl-treated UVC LEDs are enhanced by 17.1% at 500 mW and 19.5% at 100 mA, respectively, as compared to the reference. Additionally, the Cl-treated LEDs also display reduction in both the leakage current and ideality factor. Further, the photoluminescence (PL) intensity of AlGaN micro-disks is also enhanced by the Cl-treatment. X-ray photoemission spectroscopy (XPS) results indicate the formation of Cl-ITO at the ITO/p-AlGaN interface and the passivation of the surface states of AlGaN by Cl radicals. Based on the XPS results, a possible mechanism for the improved performance of Cl-treated UVC AlGaN-based LEDs is described and discussed.

    DOI: 10.1016/j.jallcom.2022.164895

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  62. Weak metastability of Al<i> <sub>x</sub> </i>Ga<sub>1-<i>x</i> </sub>N (<i>x</i>=13/24, 15/24, 17/24) shown by analyzing AlGaN grown on AlN with dense macrosteps

    Hirano, A; Nagasawa, Y; Ippommatsu, M; Sako, H; Hashimoto, A; Sugie, R; Honda, Y; Amano, H; Kojima, K; Chichibu, SF

    APPLIED PHYSICS EXPRESS   Vol. 15 ( 7 )   2022.7

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    Energy-dispersive X-ray signals calibrated by Rutherford backscattering indicated the generation of Al13/24Ga11/24N in Ga-rich stripes in a nonflat Al0.58Ga0.42N layer. Also, the CL peak wavelengths of ∼259 and 272 nm also showed the generation of Al15/24Ga9/24N and Al13/24Ga11/24N in Al-rich zones and Ga-rich stripes, respectively. The wavelength of a strong CL peak at ∼246 nm, which was observed from the Al0.7Ga0.3N layer in our previous study, is also considered to correspond to the near-band-emission wavelengths of Al17/24Ga7/24N. In particular, the stronger reproducibility of metastable Al15/24Ga9/24N generation was confirmed, in agreement with the computed predictions by other research groups.

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  63. Space-Charge Profiles and Carrier Transport Properties in Dopant-Free GaN-Based p-n Junction Formed by Distributed Polarization Doping

    Kumabe, T; Kawasaki, S; Watanabe, H; Nitta, S; Honda, Y; Amano, H

    PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS   Vol. 16 ( 7 )   2022.7

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    Herein, the operation of dopant-free GaN-based p-n junctions formed by distributed polarization doping (DPD) is experimentally demonstrated and their space charge profiles and carrier transport properties are investigated. The device exhibits ideal space charge profiles explained by polarization effects and demonstrates the excellent controllability of DPD. In addition, it shows rectification and electroluminescence under forward-biased conditions. The carrier transport properties could be explained by the conventional recombination/diffusion model used for impurity-doped p-n junctions. Repeatable breakdowns are also observed in all devices and the temperature-dependent breakdown voltages reveal that the breakdowns are caused by avalanche multiplication, which is also the same as those reported in impurity-doped GaN p-n diodes. These results indicate that DPD is a promising doping technology for GaN-based power devices overcoming any issues associated with conventional impurity doping.

    DOI: 10.1002/pssr.202200127

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  64. Dual-peak electroluminescence spectra generated from Al <i><sub>n</sub></i> <sub>/12</sub>Ga<sub>1-<i>n</i>/12</sub>N (<i>n</i>=2, 3, 4) for AlGaN-based LEDs with nonflat quantum wells

    Nagasawa, Y; Kojima, K; Hirano, A; Ippommatsu, M; Honda, Y; Amano, H; Chichibu, SF

    JOURNAL OF PHYSICS D-APPLIED PHYSICS   Vol. 55 ( 25 )   2022.6

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    The metastability of Al n/12Ga1-n/12N (n = 2, 3, and 4) was investigated by the statistical analysis of electroluminescence (EL) spectra having dual peaks with a peak-to-peak distance (pp) of >10 nm generated from nonflat Al x Ga1-x N (x ∼0.2) quantum wells (QWs) fabricated on c(0001) sapphire substrates with a miscut of 1.0° towards the m[1 1ˉ 00] axis. To explain the origins of the dual-peak EL (DPEL) spectra, which are often observed for AlGaN-QWs with Ga content of greater than 0.7, a nonflat QW model incorporating two metastable compositions, Al(n-1)/12Ga1-(n-1)/12N and Al n/12Ga1-n/12N (n: integer), is proposed. By the statistical analysis of peak wavelengths in DPEL spectra and the verification of EL spectral shapes, two series of featured EL peak wavelengths with intervals of 2-3 nm were obtained from five out of six LED wafers. The two series of featured EL peak wavelengths were assigned by comparison with the calculated EL wavelengths. Then, Al2/12Ga10/12N and Al3/12Ga9/12N were determined to be the origins of peaks with the longer and shorter wavelengths in the DPEL, respectively, in addition to the metastable Al n/12Ga1-n/12N (n= 4-9) compositions observed in our previous studies. When DPEL (pp> 10 nm) appeared, the difference in QW thickness between Al2/12Ga10/12N and Al3/12Ga9/12N tended to be larger than one monolayer (ML), indicating a significant amount of Ga or GaN mass transport. Furthermore, the Al2/12Ga10/12N and Al3/12Ga9/12N QWs are considered to have thicknesses of m ML (m: consecutive integers), suggesting the 1 ML configuration of Al and Ga atoms on the c(0001) plane. In addition, the DPEL obtained from nonflat Al x Ga1-x N (x ∼0.25) QWs by another research group was shown to be related to two metastable Al n/12Ga1-n/12N (n = 3, 4), similarly to our one exceptional LED wafer, which also agreed with the model proposed in this work.

    DOI: 10.1088/1361-6463/ac5d03

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  65. Author Correction: Laser slice thinning of GaN-on-GaN high electron mobility transistors.

    Tanaka A, Sugiura R, Kawaguchi D, Wani Y, Watanabe H, Sena H, Ando Y, Honda Y, Igasaki Y, Wakejima A, Ando Y, Amano H

    Scientific reports   Vol. 12 ( 1 ) page: 8175   2022.5

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    DOI: 10.1038/s41598-022-12628-0

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  66. Laser slice thinning of GaN-on-GaN high electron mobility transistors

    Tanaka, A; Sugiura, R; Kawaguchi, D; Wani, Y; Watanabe, H; Sena, H; Ando, Y; Honda, Y; Igasaki, Y; Wakejima, A; Ando, Y; Amano, H

    SCIENTIFIC REPORTS   Vol. 12 ( 1 ) page: 7363   2022.5

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    As a newly developed technique to slice GaN substrates, which are currently very expensive, with less loss, we previously reported a laser slicing technique in this journal. In the previous report, from the perspective of GaN substrate processing, we could only show that the GaN substrate could be sliced by a laser and that the sliced GaN substrate could be reused. In this study, we newly investigated the applicability of this method as a device fabrication process. We demonstrated the thinning of GaN-on-GaN high-electron-mobility transistors (HEMTs) using a laser slicing technique. Even when the HEMTs were thinned by laser slicing to a thickness of 50 mm after completing the fabrication process, no significant fracture was observed in these devices, and no adverse effects of laser-induced damage were observed on electrical characteristics. This means that the laser slicing process can be applied even after device fabrication. It can also be used as a completely new semiconductor process for fabricating thin devices with thicknesses on the order of 10 mm, while significantly reducing the consumption of GaN substrates.

    DOI: 10.1038/s41598-022-10610-4

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  67. Interplay of sidewall damage and light extraction efficiency of micro-LEDs

    Park, JH; Pristovsek, M; Cai, WT; Cheong, H; Kumabe, T; Lee, DS; Seong, TY; Amano, H

    OPTICS LETTERS   Vol. 47 ( 9 ) page: 2250 - 2253   2022.5

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    This Letter describes the impact of shape on micro light-emitting diodes (µLEDs), analyzing 400 µm2 area µLEDs with various mesa shapes (circular, square, and stripes). Appropriate external quantum efficiency (EQE) can yield internal quantum efficiency (IQE) which decreases with increasing peripheral length of the mesas. However, light extraction efficiency (ηe) increased with increasing mesa periphery. We introduce analysis of Jpeak (the current at peak EQE) since it is proportional to the non-radiative recombination. Etching the sidewalls using tetramethylammonium hydroxide (TMAH) increased the peak EQE and decreased the sidewall dependency of Jpeak. Quantitatively, the TMAH etching reduced non-radiative surface recombination by a factor of four. Hence, shrinking µLEDs needs an understanding of the relationship between non-radiative recombination and ηe, where analyzing Jpeak can offer new insights.

    DOI: 10.1364/OL.456993

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  68. <p>The effect of dry etching condition on the performance of blue micro light-emitting diodes with reduced quantum confined Stark effect epitaxial layer</p>

    Park Jeong-Hwan, Cai Wentao, Cheong Heajeong, Ushida Yasuhisa, Lee Da-Hoon, Ando Yuto, Furusawa Yuta, Honda Yoshio, Lee Dong-Seon, Seong Tae-Yeon, Amano Hiroshi

    JOURNAL OF APPLIED PHYSICS   Vol. 131 ( 15 )   2022.4

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    As the size of micro light-emitting diodes (μLEDs) decreases, μLEDs encounter etching damage especially at the sidewalls that critically affects their properties. In this study, we investigated the influence of etching bias power (Pbias) on the performance of μLEDs and found that the current-voltage and light output-current characteristics of μLEDs were enhanced when Pbias was reduced. It was shown that at low Pbias, the chemical reaction between etching gas and gallium nitride, rather than ion sputtering, dominated the etching process, leading to low plasma damage and rough surface morphology. Additionally, to understand the etching-induced surface roughening behaviors, various substrates with different threading dislocation densities were treated at low Pbias. It was found that for the sample (with p-contact size of 10 × 10 μm2), the efficiency droop was approximately 20%, although the current reached 10 mA due most probably to the suppressed polarization effect in the quantum well. It was further observed that the external quantum efficiency (EQE) was dependent on Pbias, where the lowest Pbias yielded the highest maximum EQE, indicating that the plasma damage was mitigated by reducing Pbias. Optimization of dry etching and polarization-suppression conditions could pave the way for realizing high-performance and brightness μLEDs for next-generation displays.

    DOI: 10.1063/5.0085384

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  69. Continuous-wave lasing of AlGaN-based ultraviolet laser diode at 274.8 nm by current injection

    Zhang, ZY; Kushimoto, M; Yoshikawa, A; Aoto, K; Schowalter, LJ; Sasaoka, C; Amano, H

    APPLIED PHYSICS EXPRESS   Vol. 15 ( 4 )   2022.4

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    We demonstrated continuous-wave lasing of an AlGaN-based ultraviolet laser diode, fabricated on a single-crystal AlN substrate when operating at 5 °C. The threshold current density and device series resistance were reduced by improvements to the epitaxial structure and electrode arrangement. A peak wavelength of 274.8 nm was observed for lasing at a drive current over 110 mA, which corresponded to a threshold current density of 3.7 kA cm-2. The operating voltage at the threshold current was as low as 9.6 V.

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  70. "Regrowth-free" fabrication of high-current-gain AlGaN/GaN heterojunction bipolar transistor with N-p-n configuration

    Kumabe, T; Watanabe, H; Ando, Y; Tanaka, A; Nitta, S; Honda, Y; Amano, H

    APPLIED PHYSICS EXPRESS   Vol. 15 ( 4 )   2022.4

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    An AlGaN/GaN heterojunction bipolar transistor (HBT) with N-p-n configuration was fabricated by the "regrowth-free"method, resulting in a contamination-free emitter-base AlGaN/GaN heterojunction. The low-bias-power-based low-damage inductively coupled plasma-reactive ion etching was employed in this study for emitter mesa definition instead of the conventional selective-area-regrowth technique. The method successfully minimized the etching-induced damage in the p-GaN base layer and the contamination at the emitter-base AlGaN/GaN heterojunction. Consequently, the fabricated device exhibited a high current gain of 25, the highest current density of 15.0 kA cm-2, and the lowest on-state voltage offset of 0.75 V ever reported for AlGaN/GaN HBTs.

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  71. Mechanism and enhancement of anti-parasitic-reaction catalytic activity of tungsten-carbide-coated graphite components for the growth of bulk GaN crystals

    Nakamura, D; Iida, K; Horibuchi, K; Aoki, Y; Takahashi, N; Mori, Y; Moriyama, M; Nitta, S; Amano, H

    APPLIED PHYSICS EXPRESS   Vol. 15 ( 4 )   2022.4

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    The working mechanism of the anti-parasitic-reaction (APR) catalyst of tungsten carbide (WC) coating on graphite in hydride vapor phase epitaxy GaN growth were examined. During NH3 annealing, the surface of WC is reduced as well as nitrided. The W2N topmost layer was found to work as an APR-active catalyst to suppress the formation of GaN polycrystals during high-rate HVPE-GaN growth, while the regions covered with thick pyrolytic graphite residues were catalytically inert. The formation of an additional W2C top layer on the WC underlayer was demonstrated to exhibit superior APR activity, i.e. complete suppression of GaN polycrystal formation.

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  72. Sputtered polycrystalline MgZnO/Al reflective electrodes for enhanced light emission in AlGaN-based homojunction tunnel junction DUV-LED

    Matsubara, T; Nagatat, K; Kushimoto, M; Tomai, S; Katsumata, S; Honda, Y; Amano, H

    APPLIED PHYSICS EXPRESS   Vol. 15 ( 4 )   2022.4

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    In this study, we enhanced the emission power of AlGaN-based tunnel junction deep-ultraviolet LEDs (TJ LEDs) by using a MgZnO and aluminum stacked structure as UV reflective electrodes on the anode side. The emission wavelength of the fabricated TJ LED was 284 nm, and the emission power was 57.3 mW at 63 A cm-2. The polycrystalline MgZnO enabled both conductivity and UV transmittance to be achieved, approximately doubling with a reflectance of the fabricated TJ LED at 284 nm compared to conventional TJ LED with Ti/Al. These factors contributed to the increased emission power of TJ LEDs.

    DOI: 10.35848/1882-0786/ac5acf

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  73. Structural design optimization of 279 nm wavelength AlGaN homojunction tunnel junction deep-UV light-emitting diode

    Nagata K., Anada S., Miwa H., Matsui S., Boyama S., Saito Y., Kushimoto M., Honda Y., Takeuchi T., Amano H.

    Applied Physics Express   Vol. 15 ( 4 )   2022.4

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    We demonstrated the structural optimization of AlGaN tunnel junction (TJ) deep-ultraviolet light-emitting diodes by changing the thickness and impurity concentrations of p+-type and n+-type AlGaN constituting the TJ. By decreasing the total thickness of the TJ to 23 nm, the operating voltage reached a minimum of 8.8 V at 63 A cm-2. Further decrease in TJ thickness markedly increases the operating voltage. This finding implies that the depletion layer width becomes greater than the TJ thickness if it is smaller than 12 nm. Therefore, we conclude that the TJ thickness must be greater than the depletion layer width.

    DOI: 10.35848/1882-0786/ac60c7

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  74. Improved device performance of vertical GaN-on-GaN nanorod Schottky barrier diodes with wet-etching process

    Liao Y., Chen T., Wang J., Cai W., Ando Y., Yang X., Watanabe H., Tanaka A., Nitta S., Honda Y., Chen K.J., Amano H.

    Applied Physics Letters   Vol. 120 ( 12 )   2022.3

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    In this work, a deliberate etching-based top-down approach is proposed to fabricate the GaN nanorod (NR) Schottky barrier diode (SBD). As a key step during the fabrication, the impact of the wet-etching process on device performance is systematically studied. By virtue of the reduced surface states at the sidewall, the performance of NR SBD with the wet-etching process is substantially improved, delivering a forward turn-on voltage of 0.65 V, a current density of ∼10 kA/cm2 at 3 V, an ideality factor of 1.03, an ON/OFF current ratio of ∼1010, and no severe current collapse, along with a reverse breakdown voltage of 772 V.

    DOI: 10.1063/5.0083194

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  75. Inhomogeneous Barrier Height Characteristics of <i>n</i>-Type AlInP for Red AlGaInP-Based Light-Emitting Diodes

    Cha, JS; Lee, DH; Sim, KB; Lee, TJ; Seong, TY; Amano, H

    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY   Vol. 11 ( 3 )   2022.3

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    For micro-light-emitting diode (LED)-based display applications, such as virtual reality and augmented reality, high-performance Ohmic contacts (namely, the improvement of current injection efficiency) is vital to the realization of high-efficiency micro-LEDs. The surface Fermi level pinning characteristics could be comprehended in terms of the relation between work function of metals (M) and Schottky barrier height (SBH, B). In this study, we have investigated the surface Fermi level pinning characteristics of (001) n-AlInP surfaces by employing Schottky diodes with different metals. With an increase in the temperature, B increases linearly and ideality factors (n) decreases. This behavior is related to the barrier height inhomogeneity. Inhomogeneity-modelbased B is evaluated to be in the range of 0.86 1.30 eV, which is dependent on the metal work functions and are similar to those measured from capacitance-voltage relation. Further, The S-parameter, the relation between B and M (d B/d M), is 0.36. This is indicative of the partial pinning of the surface Fermi level at the surface states placed at 0.95 eV below the conduction band. Furthermore, it is also shown that (NH4)2S-passivation results in an increases the mean SBH and the S-parameter (e.g., 0.52).

    DOI: 10.1149/2162-8777/ac5d66

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  76. Visualization of depletion layer in AlGaN homojunction p-n junction

    Nagata, K; Anada, S; Saito, Y; Kushimoto, M; Honda, Y; Takeuchi, T; Yamamoto, K; Hirayama, T; Amano, H

    APPLIED PHYSICS EXPRESS   Vol. 15 ( 3 )   2022.3

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    We analyzed the p-n junction of an aluminum gallium nitride (AlGaN) homojunction tunnel junction (TJ) deep-ultraviolet light-emitting diode by phase-shifting electron holography. We clearly obtained a phase image reflecting the band alinement of the p-n homojunction and derived a depletion layer width of approximately 10 nm. In addition, the observed depletion layer width for the AlGaN TJ was in good agreement with the simulated one reflecting the diffusion profile of Mg and Si, thus enabling a discussion on the electrical conduction mechanism for an AlGaN p-n junction.

    DOI: 10.35848/1882-0786/ac53e2

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  77. Effect of beam current on defect formation by high-temperature implantation of Mg ions into GaN

    Itoh, Y; Watanabe, H; Ando, Y; Kano, E; Deki, M; Nitta, S; Honda, Y; Tanaka, A; Ikarashi, N; Amano, H

    APPLIED PHYSICS EXPRESS   Vol. 15 ( 2 )   2022.2

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    We evaluated the beam current dependence of defect formation during Mg ion implantation into GaN at a high temperature of 1100 °C with two beam currents. Photoluminescence spectra suggest that low-beam-current implantation reduced the vacancy concentration and activated Mg to a greater extent. Moreover, scanning transmission electron microscopy analysis showed that low-beam-current implantation reduced the density of Mg segregation defects with inactive Mg and increased the density of intrinsic dislocation loops, suggesting decreases in the densities of Ga and N vacancies. The formation of these defects depended on beam current, which is an important parameter for defect suppression.

    DOI: 10.35848/1882-0786/ac481b

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  78. Defect characterization of { 10 1 ¯ 3 } GaN by electron microscopy

    Kusch G., Frentrup M., Hu N., Amano H., Oliver R.A., Pristovsek M.

    Journal of Applied Physics   Vol. 131 ( 3 )   2022.1

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    Advances in obtaining untwinned (10 1 ¯3)-oriented semi-polar GaN enable a new crystal orientation for the growth of green and red LED structures. We present a scanning electron microscopy study that combines the structural characterization of electron channeling contrast imaging with the optical characterization of cathodoluminescence hyperspectral imaging on a (10 1 ¯ 3) GaN layer. An extensive defect analysis revealed that the dominant defects consist of basal plane stacking faults (BSFs), prismatic stacking faults, partial dislocations, and threading dislocations. With a defect density of about an order of magnitude lower than in comparable. The optical properties of the defects have been characterized from 10 to 320 K, showing BSF luminescence at room temperature indicating a reduced density of non-radiative recombination centers in the as-grown samples compared to established semi- and non-polar orientations. Our findings suggest that growth along (10 1 ¯3) has the potential for higher radiative efficiency than established semi-polar orientations.

    DOI: 10.1063/5.0077084

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  79. Perspective on thermal conductance across heterogeneously integrated interfaces for wide and ultrawide bandgap electronics

    Cheng, Z; Graham, S; Amano, H; Cahill, DG

    APPLIED PHYSICS LETTERS   Vol. 120 ( 3 )   2022.1

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    Heterogeneous integration is important to create multi-functionality in future electronic devices. However, few thermal studies of the interfaces formed in these integrated devices have been reported before. Recently, integrated interfaces by surface-Activated bonding were found to have high thermal boundary conductance, which provides a solution for heat dissipation of GaN and β-Ga2O3-based power electronics. Here, we review the recent progress on the interfacial thermal transport across heterogeneously integrated interfaces, including transferred van der Waals force bonded interfaces, surface-Activated bonded interfaces, plasma bonded interfaces, and hydrophilic bonded interfaces. This Perspective specifically focuses on applications of thermal management strategies of electronics, especially power electronics. Finally, the challenges, such as high-Throughput thermal measurements of buried interfaces, thermal property-structure relations of interfaces bonded under different conditions, theoretical understanding of interfacial thermal transport, and device demonstrations, are pointed out.

    DOI: 10.1063/5.0077039

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  80. Threshold increase and lasing inhibition due to hexagonal-pyramid-shaped hillocks in AlGaN-based DUV laser diodes on single-crystal AlN substrate

    Kushimoto, M; Zhang, ZY; Honda, Y; Schowalter, LJ; Sasaoka, C; Amano, H

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 61 ( 1 )   2022.1

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    The presence of hexagonal-pyramid-shaped hillocks (HPHs) in AlGaN epitaxial films affects device characteristics; this effect is significant in DUV laser diodes (LDs) on AlN substrates, where the presence of HPHs under the p-electrode increases the threshold current density and inhibits the lasing. In this study, we investigated the difference between the lasing characteristics of LDs with and without HPHs. It was found that in the presence of HPHs, the threshold excitation power density increased and the slope efficiency decreased by optical excitation. To investigate the cause of these phenomena, we performed structural, optical, and electrical analyses of the HPHs. Various imaging techniques were used to directly capture the characteristics of the HPHs. As a result, we concluded that HPHs cause the degradation of LD characteristics due to a combination of structural, optical, and electrical factors.

    DOI: 10.35848/1347-4065/ac3a1d

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  81. Ohmic Contact to <i>p</i>-Type GaN Enabled by Post-Growth Diffusion of Magnesium

    Wang, J; Lu, S; Cai, WT; Kumabe, T; Ando, Y; Liao, YQ; Honda, Y; Xie, YH; Amano, H

    IEEE ELECTRON DEVICE LETTERS   Vol. 43 ( 1 ) page: 150 - 153   2022.1

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    We demonstrated the formation of excellent Ohmic contact to p-type GaN (including the plasma etching-damaged p-type GaN which otherwise exhibited undetectable current within ±5 V) by the post-growth diffusion of magnesium. The specific contact resistivity on the order of 10-4Omega cm2 (extracted at V=0 V) was achieved on the plasma-damaged p-GaN with linear current-voltage characteristics by the transfer length method (TLM) measurement. The improvement in current by a factor of over 109 was also obtained on the plasma-damaged p-n junction diode after the same Mg-treatment. These experimental results indicate a great potential of post-growth diffusion of Mg to overcome the bottleneck of forming a good Ohmic contact to p-GaN.

    DOI: 10.1109/LED.2021.3131057

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  82. Frontier electronics in memory of Professor Isamu Akasaki

    Amano, H

    GALLIUM NITRIDE MATERIALS AND DEVICES XVII   Vol. 12001   2022

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    ISAMU AKASAKI, crystal grower, a pioneer of GaN-based blue light-emitting diodes (LEDs), and a Nobel Laureate in Physics, passed away because of pneumonia on April 1, 2021 at the age of 92. According to the Nobel Foundation, the LED lamp holds considerable promise for improving the quality of life of over 1.5 billion people worldwide who lack access to electricity grids. Owing to its low power requirements, it can be powered by cheap local solar energy. In this article, his pursuit of blue LEDs for 20 years is described.

    DOI: 10.1117/12.2619005

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  83. An Accurate Approach to Develop Small Signal Circuit Models for AlGaN/GaN HEMTs Using Rational Functions and Dependent Current Sources

    Jadhav, A; Ozawa, T; Baratov, A; Asubar, JT; Kuzuhara, M; Wakejima, A; Yamashita, S; Deki, M; Nitta, S; Honda, Y; Amano, H; Roy, S; Sarkar, B

    IEEE JOURNAL OF THE ELECTRON DEVICES SOCIETY   Vol. 10   page: 797 - 807   2022

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    In this paper, a technique to develop small signal circuit (SSC) models of AlGaN/GaN high electron mobility transistors (HEMTs) using dependent current sources is presented. In this technique, experimentally measured broadband Y-parameters of AlGaN/GaN HEMTs are mathematically modeled as a sum of pole-residue terms. By representing each pole-residue term as a dependent current source, it is possible to develop an accurate SSC models for HEMTs which otherwise may not be possible using passive resistive-inductive-capacitive elements. The accuracy of the proposed SSC model is validated against the conventional SSC model using a 2nd, 3rd and 4th order rational function representation of the admittance branches of AlGaN/GaN HEMTs. Therefore, the proposed SSC model turns out to be highly robust in nature and can take care of any form of the transfer functions of the admittance branches between the gate, drain, and source terminal of an AlGaN/GaN HEMT.

    DOI: 10.1109/JEDS.2022.3208028

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  84. Promising Results of National Project by Japanese Ministry of the Environment to Develop GaN on GaN Power Devices and Prove their Usefulness in Real Systems

    Otoki Y., Shibata M., Mishima T., Ohta H., Mori Y., Imanishi M., Tamura S., Kidera K., Takino J., Okayama Y., Watanabe K., Okamoto N., Honda Y., Yamamoto M., Shiozaki K., Amano H.

    2022 International Conference on Compound Semiconductor Manufacturing Technology, CS MANTECH 2022     page: 237 - 242   2022

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    Exciting high performance power electronic devices have been widely demonstrated and manufactured using GaN epitaxial layers, but the majority of these devices have been fabricated on lattice mismatched substrates, including SiC, Si, or sapphire. Unfortunately, using lattice mismatched substrates inevitably introduces high concentrations of point defects and dislocations into the GaN epilayers, and these defects degrade the electrical performance of the fabricated GaN devices. Also, the mismatch of lattice constant and coefficient of thermal expansion cause strain and wafer bowing in the GaN epi, which further degrade the quality material for device fabrication. Using lattice matched GaN substrates provides solutions to these problems. In 2014, the Ministry of the Environment launched a national project to develop the required technology and to prove the superiority of GaN on GaN devices in real systems, with more than 10 partnerships from academia and industry. The project included work in several areas, including GaN substrate growth, GaN epitaxy, material characterization, and fabrication of devices and ICs for application in various systems. Large area GaN substrates have been grown with low defect densities, which has enabled fabrication of new types of vertical and horizontal GaN devices. The GaN devices have been used in servers, solar cell power conditioners, microwave ICs, distribution transformers, electric vehicle power converters. The performance improvements were compared with conventional approaches in each case. An “ALL GaN vehicle” has also been demonstrated, in which GaN devices are used in all power components. In this talk, we will present these results which show the great potential of GaN on GaN devices in the industry.

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  85. Development of Desktop Air Curtain System to Block Aerosols in Exhaled Breath

    TAKAMURE Kotaro, SAKAMOTO Yasuaki, YAGI Tetsuya, IWATANI Yasumasa, AMANO Hiroshi, UCHIYAMA Tomomi

    The Proceedings of Mechanical Engineering Congress, Japan   Vol. 2022 ( 0 ) page: S055-10   2022

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    <p>A desktop-type air curtain device capable of being installed on a desk to protect healthcare workers from infectious diseases was developed. Pseudo-exhaled air containing aerosol particles emitted from a mannequin was blown toward the air curtain generated by the air curtain device. The aerosol blocking effect of the air curtain device was investigated using particle image velocimetry measurements. Air curtain flow was maintained inside the gate of the air curtain device. The aerosol particles approaching the air curtain device were observed to abruptly bend towards the suction port without passing through the gate, signifying that the aerosol particles were blocked by the air curtain flow.</p>

    DOI: 10.1299/jsmemecj.2022.s055-10

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  86. Collection and Inactivation Abilities of Virus Flowing in a Return Air Channel with a DUV- LED

    TAKAMURE Kotaro, IWATANI Yasumasa, SAKAMOTO Yasuaki, YAGI Tetsuya, AMANO Hiroshi, UCHIYAMA Tomomi

    The Proceedings of Mechanical Engineering Congress, Japan   Vol. 2022 ( 0 ) page: S055-11   2022

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    <p>A virus inactivation unit that can inactivate viruses was developed using deep ultraviolet (DUV) LEDs that emit DUV rays with a wavelength of 280 nm. The flow characteristics of virus particles inside the virus inactivation unit were investigated using numerical simulations. The percentage of particles colliding on the inner wall of the virus inactivation unit is 56 %. Especially, many particles collide with the partition plates behind the sharp-turn parts.</p>

    DOI: 10.1299/jsmemecj.2022.s055-11

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  87. Blocking and collecting effect of aerosol particles by desktop air curtain system

    TAKAMURE Kotaro, KOBAYASHI Daisuke, MUTO Hiromasa, HARUKI Taketo, AMANO Hiroshi, YAGI Tetsuya, IWATANI Yasumasa, UCHIYAMA Tomomi

    The Proceedings of the Fluids engineering conference   Vol. 2022 ( 0 ) page: OS03-22   2022

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    DOI: 10.1299/jsmefed.2022.os03-22

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  88. Ohmic contact on low-doping-density p-type GaN with nitrogen-annealed Mg

    Lu, S; Deki, M; Wang, J; Ohnishi, K; Ando, Y; Kumabe, T; Watanabe, H; Nitta, S; Honda, Y; Amano, H

    APPLIED PHYSICS LETTERS   Vol. 119 ( 24 )   2021.12

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    We have demonstrated a fabrication process for the Ohmic contact on low-doping-density p-type GaN with nitrogen-annealed Mg. An Ohmic contact with a contact resistance of 0.158 ω cm2 is realized on p-GaN ([Mg] = 1.3 × 1017 cm-3). The contact resistance of p-type GaN with higher Mg concentration ([Mg]=1.0 × 1019 cm-3) can also be reduced to 2.8 × 10-5 ω cm2. A localized contact layer is realized without any etching or regrowth damage. The mechanism underlying this reduced contact resistance is studied by scanning transmission electron microscopy with energy dispersive x-ray spectroscopy and secondary ion mass spectrometry, representing a mutual diffusion of Ga and Mg atoms on the interface. Reductions in the barrier height and surface depletion width with the nitrogen-annealed Mg layer are confirmed by XPS and Hall effect measurements qualitatively.

    DOI: 10.1063/5.0076764

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  89. Uniting a III-Nitride Transmitter, Waveguide, Modulator, and Receiver on a Single Chip

    Xie, MY; Jiang, Y; Gao, XM; Cai, W; Yuan, JL; Zhu, HB; Wang, YJ; Zeng, XF; Zhang, ZY; Liu, YH; Amano, H

    ADVANCED ENGINEERING MATERIALS   Vol. 23 ( 12 )   2021.12

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    The integration of III-nitride electronics and photonics is of great interest toward future computing systems with low power consumption. Multifunctioning multiple quantum well (MQW) diodes can address the challenging issue for on-chip integration of a light source, which is a key component to drive the photonic circuits. Herein, a transmitter, waveguide, modulator, and receiver are monolithically integrated on a III-nitride-on-silicon platform to perform light emission, transmission, modulation, and detection simultaneously. Both the receiver and modulator exhibit sufficient sensitivity to optical signals from the transmitter, which has an identical InGaN/AlGaN multiple quantum well (MQW) structure because the III-nitride diode provides spectral overlap between the emission and absorption spectra. On-chip data communication among these optical components is achieved using light, and the effective wavelength range is from 365 to 385 nm, in which multifunctional devices can be operated.

    DOI: 10.1002/adem.202100582

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  90. Discrete wavelengths observed in electroluminescence originating from Al<inf>1/2</inf>Ga<inf>1/2</inf>N and Al<inf>1/3</inf>Ga<inf>2/3</inf>N created in nonflat AlGaN quantum wells

    Nagasawa Y., Kojima K., Hirano A., Sako H., Hashimoto A., Sugie R., Ippommatsu M., Honda Y., Amano H., Chichibu S.F.

    Journal of Physics D: Applied Physics   Vol. 54 ( 48 )   2021.12

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    When nonflat Al x Ga1-x N quantum wells (QWs) for producing 285 nm light emitting diodes (LEDs) were fabricated on n-AlGaN on AlN templates with dense macrosteps on c(0001) sapphire substrates with a 1.0 miscut relative to the m[1-100] axis, composite electroluminescence (EL) spectra from both inclined and terrace zones in Al x Ga1-x N QWs (x∼ 1/3) were generated owing to compositional and thickness modulations. The shoulder or main peaks in composite EL spectra tended to locate at fixed discrete wavelengths of ∼287, ∼292, and ∼296 nm from 12 nonuniform 285 nm LED wafers that were involved in nonnegligible run-to-run drift, even though these wafers were fabricated using the same source gas flow parameters for metal-organic vapor phase epitaxy. The discrete wavelengths of ∼287, ∼292, and ∼296 nm were attributed to EL from Al1/3Ga2/3N QWs with thicknesses of 8, 9, and 10 monolayers (ML), respectively, by referring to the results of cathodoluminescence (CL) analysis. Also, when nonflat Al x Ga1-x N QWs (x∼ 1/2) for 265 nm LEDs were grown, single-peak-like EL spectra were mainly generated from the inclined zones in nonflat QWs. The EL spectra taken from four nonuniform 265 nm LED wafers tended to show weak structures or main peaks at ∼257, ∼261, ∼266, and ∼271 nm, which were also attributed to emissions from Al1/2Ga1/2N QWs with thicknesses of 5, 6, 7, and 8 ML, respectively, by referring to CL analysis results. The creation of Al1/3Ga2/3N and Al1/2Ga1/2N in nonflat QWs in this work was in agreement with the results of our previous studies that indicated the creation of metastable Al n/12Ga1-n/12N (n: consecutive natural numbers). Furthermore, QW thicknesses of consecutive n ML may imply that Al1/3Ga2/3N and Al1/2Ga1/2N have 1 ML configurations of Al and Ga atoms on a c(0001) plane.

    DOI: 10.1088/1361-6463/ac2065

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  91. Multiple electron beam generation from InGaN photocathode

    Sato Daiki, Shikano Haruka, Koizumi Atsushi, Nishitani Tomohiro, Honda Yoshio, Amano Hiroshi

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B   Vol. 39 ( 6 )   2021.12

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    In this study, we generated 25 multielectron beam (MEB) using an InGaN photocathode with a negative electron affinity state irradiating with 25 multilaser beam. The uniformity of the MEB and the total electron beam current were evaluated. A laser beam was split into 25 laser beams using a spatial light modulator. The coefficient of variation (CV) of laser power was 20%. The CV of quantum efficiency was 1.1%. The CV of electron beam current was 12%, and the total current was about 1.2 μA. These results will enhance the development of the MEB-defect inspection using the InGaN photocathode.

    DOI: 10.1116/6.0001272

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  92. Modified Small Signal Circuit of AlGaN/GaN MOS-HEMTs Using Rational Functions

    Jadhav, A; Ozawa, T; Baratov, A; Asubar, JT; Kuzuhara, M; Wakejima, A; Yamashita, S; Deki, M; Nitta, S; Honda, Y; Amano, H; Roy, S; Sarkar, B

    IEEE TRANSACTIONS ON ELECTRON DEVICES   Vol. 68 ( 12 ) page: 6059 - 6064   2021.12

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    Conventional lumped small signal circuit (SSC) models of AlGaN/GaN metal oxide semiconductor high electron mobility transistors (MOS-HEMTs) are derived from the low frequency portion of the experimentally measured ${Y}$ -parameters. Consequently, these models cannot faithfully capture the high frequency behavior of the device. In this work, modified SSC models of AlGaN/GaN MOS-HEMTs are developed by fitting the entire broadband measured ${Y}$ -parameters of the device with rational functions. These rational functions are then physically realized using additional passive circuit elements added to the conventional SSC model. The accuracy of the proposed SSC models can be improved by increasing the order of the rational functions. The proposed models are demonstrably more accurate than the conventional SSC models in estimating the higher order poles and zeroes present in the experimentally measured ${Y}$ -parameters of AlGaN/GaN MOS-HEMTs.

    DOI: 10.1109/TED.2021.3119528

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  93. Vertical GaN p<SUP>+</SUP>-n junction diode with ideal avalanche capability grown by halide vapor phase epitaxy (vol 119, 152102, 2021)

    Ohnishi, K; Kawasaki, S; Fujimoto, N; Nitta, S; Watanabe, H; Honda, Y; Amano, H

    APPLIED PHYSICS LETTERS   Vol. 119 ( 20 )   2021.11

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    After the paper was published,1we found errors in the manuscript shown in page 152102-2. In the original published article, the SIMS detec-tion limits of [O] and [H] were written as 7 × 1015and 3 × 1015cm-3, respectively. The corrected detection limits of [O] and [H] are 6 × 1015and 3 × 1016cm-3, respectively. The SIMS depth profiles shown in Fig. 2(b) and the conclusions of the paper are not affected by this erratum.

    DOI: 10.1063/5.0077364

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  94. OBITUARY Isamu Akasaki

    Amano, H

    PHYSICS TODAY   Vol. 74 ( 11 ) page: 63 - 63   2021.11

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  95. Vertical GaN p<SUP>+</SUP>-n junction diode with ideal avalanche capability grown by halide vapor phase epitaxy

    Ohnishi, K; Kawasaki, S; Fujimoto, N; Nitta, S; Watanabe, H; Honda, Y; Amano, H

    APPLIED PHYSICS LETTERS   Vol. 119 ( 15 )   2021.10

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    A vertical GaN p+-n junction diode with an ideal breakdown voltage was grown by halide vapor phase epitaxy (HVPE). A steep p+-n interface was observed even with the use of the HVPE method. No Si-accumulating layer was formed at the p+-n interface because of the continuous HVPE growth from the n-type drift layer to the p-type layer. This method provides improved electrical properties compared with the regrowth of p-type GaN layers. The minimum ideality factor of approximately 1.6 was obtained. The breakdown voltage increased from 874 to 974 V with the increase in the temperature from 25 to 200 °C, which suggests that avalanche multiplication causes the breakdown. The temperature-dependent breakdown voltage was in good agreement with the breakdown voltage calculated using the ideal critical electric field. These results indicate that HVPE is promising for the fabrication of vertical GaN power devices.

    DOI: 10.1063/5.0066139

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  96. Effective neutron detection using vertical-type BGaN diodes

    Nakano, T; Mochizuki, K; Arikawa, T; Nakagawa, H; Usami, S; Honda, Y; Amano, H; Vogt, A; Schuett, S; Fiederle, M; Kojima, K; Chichibu, SF; Inoue, Y; Aoki, T

    JOURNAL OF APPLIED PHYSICS   Vol. 130 ( 12 )   2021.9

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    In this study, vertical-type thick BGaN PIN diodes were successfully fabricated to improve the neutron capture rate of BGaN diodes by improving the BGaN epitaxial growth technique. In this technique, 5-μm-thick epitaxial growth was achieved using trimethylboron as a B metal-organic source, which suppressed the gas-phase reaction. The α-particle energy spectrum, the neutron pulse signal, and the residual energy of particles emitted from a neutron capture reaction were measured using the fabricated BGaN diodes by performing radiation detection measurements. The detected signal position in the neutron detection signal spectrum was similar to that of 2.3 MeV α-particles. These results indicate that vertical-type BGaN diodes can be used as effective neutron detectors.

    DOI: 10.1063/5.0051053

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  97. Smart-cut-like laser slicing of GaN substrate using its own nitrogen

    Tanaka, A; Sugiura, R; Kawaguchi, D; Yui, T; Wani, Y; Aratani, T; Watanabe, H; Sena, H; Honda, Y; Igasaki, Y; Amano, H

    SCIENTIFIC REPORTS   Vol. 11 ( 1 ) page: 17949   2021.9

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    We have investigated the possibility of applying lasers to slice GaN substrates. Using a sub-nanosecond laser with a wavelength of 532 nm, we succeeded in slicing GaN substrates. In the laser slicing method used in this study, there was almost no kerf loss, and the thickness of the layer damaged by laser slicing was about 40 µm. We demonstrated that a standard high quality homoepitaxial layer can be grown on the sliced surface after removing the damaged layer by polishing.

    DOI: 10.1038/s41598-021-97159-w

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  98. Effects of Current, Temperature, and Chip Size on the Performance of AlGaInP-Based Red Micro-Light-Emitting Diodes with Different Contact Schemes

    Lee, DH; Lee, SY; Shim, JI; Seong, TY; Amano, H

    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY   Vol. 10 ( 9 )   2021.9

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    We have investigated the performance of AlGaInP-based red micro-light-emitting diodes (micro-LEDs) with different n-type contact schemes as functions of current, ambient temperature, and chip size. The samples with AuGe/Ni/Au contact revealed wider full width at half maximum of electroluminescence than that with the Pd/Ge contact. All samples also exhibited broad peaks at wavelengths between ∼632 and ∼640 nm, whose intensity depended on the type of contact schemes and temperature. Regardless of the contact schemes, the 10 μm-size samples showed a larger temperature-dependent reduction in the output power at current density of <50 A cm-2 than the 100 μm-size ones. Above 100 A cm-2, however, both samples showed similar temperature dependence. Irrespective of the contact schemes, the main peak of the 100-μm samples was red-shifted, whereas no red-shift was detected in the 10-μm samples. The third peak of the AuGe-based contact samples became more dominant at 700 A cm-2 than the main peak, whereas that of the PdGe contact samples became more dominant at 1000 A cm-2. Based on the chip size, current, contact scheme, and temperature dependence, the performance degradation of the red micro-LEDs is described and discussed.

    DOI: 10.1149/2162-8777/ac2029

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  99. Quasi-ballistic thermal conduction in 6H-SiC

    Cheng, Z; Lu, W; Shi, J; Tanaka, D; Protik, NH; Wang, S; Iwaya, M; Takeuchi, T; Kamiyama, S; Akasaki, I; Amano, H; Graham, S

    MATERIALS TODAY PHYSICS   Vol. 20   2021.9

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    The minimization of electronics makes heat dissipation of related devices an increasing challenge. When the size of materials is smaller than the phonon mean free paths, phonons transport without internal scattering and laws of diffusive thermal conduction need to be revisited. This work reports the temperature dependent thermal conductivity of doped epitaxial 6H–SiC and monocrystalline porous 6H–SiC below room temperature probed by time-domain thermoreflectance. Strong quasi-ballistic thermal transport was observed in these samples, especially at low temperatures. Doping and structural boundaries were applied to tune the quasi-ballistic thermal transport since dopants selectively scatter high-frequency phonons while boundaries scatter phonons with long mean free paths. Exceptionally strong phonon scattering by boron dopants are observed, compared to nitrogen dopants. Furthermore, orders of magnitude reduction in the measured thermal conductivity was observed at low temperatures for the porous 6H–SiC compared to the epitaxial 6H–SiC. Finally, first principles calculations and a simple Callaway model are built to understand the measured thermal conductivities. Our work sheds light on the fundamental understanding of thermal conduction in technologically-important wide bandgap semiconductors such as 6H–SiC and will impact applications such as thermal management of 6H–SiC-related electronics and devices.

    DOI: 10.1016/j.mtphys.2021.100462

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  100. Gallium nitride wafer slicing by a sub-nanosecond laser: effect of pulse energy and laser shot spacing

    Sena, H; Tanaka, A; Wani, Y; Aratani, T; Yui, T; Kawaguchi, D; Sugiura, R; Honda, Y; Igasaki, Y; Amano, H

    APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING   Vol. 127 ( 9 )   2021.9

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    Gallium nitride (GaN)-based devices surpass the traditional silicon-based power devices in terms of higher breakdown voltage, faster-switching speed, higher thermal conductivity, and lower on-resistance. However, heteroepitaxial GaN growths like GaN on sapphire are not suitable for power devices due to the threading dislocation densities as high as 108/cm2. Recently, homoepitaxial GaN growth has become possible thanks to the native GaN substrates with dislocation densities in the order of 104/cm2 but the extremely high cost of the GaN substrates makes the homoepitaxy method unacceptable for industrial applications, and the slicing of wafers for reusing them is an effective solution for cost reduction. In this study, we will investigate a route for slicing the GaN single crystal substrate by controlling the laser pulse energy and changing the distance between each laser shot. The 2D and 3D crack propagations are observed by a multiphoton confocal microscope, and the cross section of samples is observed by a scanning electron microscope (SEM). The results showed that two types of radial and lateral cracking occurred depending on the pulse energy and shot pitch, and controlling them was of importance for attaining a smooth GaN substrate slicing. Cross-sectional SEM images showed that at suitable pulse energy and distance, crack propagation could be controlled with respect to the irradiation plane.

    DOI: 10.1007/s00339-021-04808-y

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  101. High-Gain Gated Lateral Power Bipolar Junction Transistor

    Wang, J; Xie, YH; Amano, H

    IEEE ELECTRON DEVICE LETTERS   Vol. 42 ( 9 ) page: 1370 - 1373   2021.9

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    We demonstrated a prototype Gated Lateral power bipolar junction transistor (GLP-BJT) on wide bandgap semiconductor. The device combined the intrinsic advantages of high current gain of a Gated Lateral-BJT and good current handling and voltage blocking capabilities of GaN material. As a result, the common-emitter current gain remained over 300 at a high collector current density of 2 kA/cm2 despite a wide p-base region of 2 &#x03BC;m. The open base breakdown voltage BVCEO was over 300 V corresponding to a high critical field of 2.5 MV/cm. These figures of merit show great promise of GaN-based GLP-BJT in power applications and also shed light on the development of state-of-the-art bipolar transistors based on other wide bandgap semiconductors.

    DOI: 10.1109/LED.2021.3099982

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  102. Stable electrical performance of AlGaInP-based red micro-light emitting diode by controlling interfacial morphologies of metal contacts

    Lee D.H., Seong Tae-Yeon, Amano Hiroshi

    Journal of Alloys and Compounds   Vol. 872   page: 159629   2021.8

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    DOI: 10.1016/j.jallcom.2021.159629

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  103. Improving light output power of AlGaN-based deep-ultraviolet light-emitting diodes by optimizing the optical thickness of p-layers

    Matsukura, Y; Inazu, T; Pernot, C; Shibata, N; Kushimoto, M; Deki, M; Honda, Y; Amano, H

    APPLIED PHYSICS EXPRESS   Vol. 14 ( 8 )   2021.8

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    In this study, we investigated the relationship of light output power with the optical thickness of the p-layers in AlGaN-based deep ultraviolet light-emitting diodes with a transparent high-Al-composition p-AlGaN clad layer, a thin p-GaN contact layer, and a reflective p-type electrode. By adjusting the thickness of the transparent high-Al-composition p-AlGaN clad layer, we observed a marked change in light output power. A maximum light output power of 385 mW at 1500 mA, a maximum external quantum efficiency of 15.7% at 10 mA, and a maximum wall-plug efficiency of 15.3% at 10 mA were obtained at an emission wavelength of 275 nm.

    DOI: 10.35848/1882-0786/ac154c

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  104. Reduction in operating voltage of AlGaN homojunction tunnel junction deep-UV light-emitting diodes by controlling impurity concentrations

    Nagata K., Makino H., Miwa H., Matsui S., Boyama S., Saito Y., Kushimoto M., Honda Y., Takeuchi T., Amano H.

    Applied Physics Express   Vol. 14 ( 8 )   2021.8

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    We reduced the operating voltage of AlGaN homojunction tunnel junction (TJ) deep-ultraviolet (UV) light-emitting diodes (LEDs) by two approaches: the suppression of carbon incorporation and the doping of a high concentration of silicon in an n+-AlGaN layer. The AlGaN homojunction TJ deep-UV LEDs had a significantly reduced forward voltage upon suppressing the incorporation of carbon in the n+-AlGaN layer. The suppression of electron compensation by carbon in nitrogen sites and the doping of a high concentration of silicon in an n+-AlGaN layer are important for reducing the operating voltage of AlGaN homojunction TJ deep-UV LEDs.

    DOI: 10.35848/1882-0786/ac0fb6

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  105. Impact of gate electrode formation process on Al<inf>2</inf>O<inf>3</inf>/GaN interface properties and channel mobility

    Ando Y., Deki M., Watanabe H., Taoka N., Tanaka A., Nitta S., Honda Y., Yamada H., Shimizu M., Nakamura T., Amano H.

    Applied Physics Express   Vol. 14 ( 8 )   2021.8

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    The interface properties of GaN metal-insulator-semiconductor (MIS) structures with a gate electrode metal deposited by electron beam (EB) or resistive heating evaporation were investigated. Also, the impact of the interface properties on the channel mobility in GaN MIS field-effect transistors was investigated. It was confirmed that interface charges including both interface states and positive fixed charges were introduced to an Al2O3/GaN interface by the formation of a gate electrode by EB evaporation. Consequently, the introduced interface charges degraded the electron mobility in the MIS channel.

    DOI: 10.35848/1882-0786/ac0ffa

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  106. Electrical properties and structural defects of p-type GaN layers grown by halide vapor phase epitaxy

    Ohnishi, K; Amano, Y; Fujimoto, N; Nitta, S; Watanabe, H; Honda, Y; Amano, H

    JOURNAL OF CRYSTAL GROWTH   Vol. 566   2021.7

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    The electrical properties and structural defects of p-type GaN layers with Mg concentrations from 8.0 × 1018 to 8.3 × 1019 cm−3 grown by halide vapor phase epitaxy (HVPE) were investigated. In all samples, p-type conduction was confirmed at room temperature. The hole concentration at room temperature decreased in a heavily Mg-doped sample. By analyzing the results of Hall-effect measurements at various temperatures, the acceptor concentration decreased in a heavily Mg-doped sample, whereas the compensating donor concentration increased. These results affect the decrease in the hole concentration. The hole mobility decreased with increasing acceptor concentration. In the heavily Mg-doped sample, pyramidal inversion domains (PIDs) were formed. The size of each PID in an HVPE-grown sample is in good agreement with that Mg-doped GaN layers grown by metalorganic vapor phase epitaxy (MOVPE). Thus, the formation mechanism of PIDs in HVPE-grown samples is possibly the same as that in MOVPE-grown samples. Energy-dispersive X-ray spectroscopy shows that Mg atoms accumulate in PIDs, which suggests that Mg atoms in PIDs are electrically inactive, inhibiting the increase in the acceptor concentration. These results are useful guidelines for fabricating p-type GaN layers with higher hole concentrations by HVPE.

    DOI: 10.1016/j.jcrysgro.2021.126173

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  107. 赤﨑勇先生のご逝去を悼む

    天野 浩

    応用物理   Vol. 90 ( 7 ) page: 455 - 455   2021.7

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    DOI: 10.11470/oubutsu.90.7_455

    CiNii Research

  108. 赤﨑 勇先生を偲んで

    天野 浩

    日本物理学会誌   Vol. 76 ( 7 ) page: 478 - 478   2021.7

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    <p>追悼</p><p>赤﨑 勇先生を偲んで</p>

    DOI: 10.11316/butsuri.76.7_478

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  109. Vertical GaN-on-GaN nanowire Schottky barrier diodes by top-down fabrication approach

    Liao Y., Chen T., Wang J., Ando Y., Cai W., Yang X., Watanabe H., Hirotani J., Tanaka A., Nitta S., Honda Y., Chen K.J., Amano H.

    Japanese Journal of Applied Physics   Vol. 60 ( 7 )   2021.7

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    An optimized top-down approach was utilized to fabricate vertical GaN-on-GaN nanowire Schottky barrier diodes (NWSBDs) in this letter. The suppressed reverse leakage current and enhanced breakdown voltage (BV) of the vertical GaN NWSBDs are attributed to the reduced electric field at the interface of the Schottky junction achieved through the dielectric reduced surface field technique. As-fabricated NWSBD delivers a low turn-on voltage of 0.80 V, a near-unity ideality factor of 1.04, along with a soft BV of 480 V. The measured soft BV is comparable with the avalanche BV of the p-n diode with a similar net doping concentration in the drift region.

    DOI: 10.35848/1347-4065/ac06b5

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  110. Isamu Akasaki: The Pioneer of Blue LEDs and his Collaboration with <i>pss</i> OBITUARY

    Amano, H

    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE   Vol. 218 ( 14 )   2021.7

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    DOI: 10.1002/pssa.202100329

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  111. Non-polar true-lateral GaN power diodes on foreign substrates

    Wang, J; Yu, G; Zong, H; Liao, YQ; Lu, WF; Cai, WT; Hu, XD; Xie, YH; Amano, H

    APPLIED PHYSICS LETTERS   Vol. 118 ( 21 )   2021.5

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    We have demonstrated non-polar GaN power diodes (Schottky barrier diode and p-n junction diode) on foreign substrates featuring the true-lateral p-n and metal-semiconductor junctions. The diodes were fabricated on GaN islands laterally overgrown on the mask-patterned sapphire and Si substrates by metalorganic vapor phase epitaxy. The anode and cathode were formed on the opposed a-plane sidewalls of the island, making the device architecture essentially like the 90° rotation of the desired true-vertical power diodes. The ideality factor of the Schottky barrier diode remained 1.0 (from 1.00 to 1.05) over 7 decades in current. Specifically, a high critical electric field of 3.3 MV/cm was demonstrated on the p-n junction diode with avalanche capability. These performances reveal a strong potential of non-polar GaN with the true-lateral junctions for high power applications.

    DOI: 10.1063/5.0051552

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  112. The stability of graphene and boron nitride for III-nitride epitaxy and post-growth exfoliation.

    Park JH, Yang X, Lee JY, Park MD, Bae SY, Pristovsek M, Amano H, Lee DS

    Chemical science   Vol. 12 ( 22 ) page: 7713 - 7719   2021.5

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    A challenging approach, but one providing a key solution to material growth, remote epitaxy (RE)—a novel concept related to van der Waals epitaxy (vdWE)—requires the stability of a two-dimensional (2-D) material. However, when graphene, a representative 2-D material, is present on substrates that have a nitrogen atom, graphene loss occurs. Although this phenomenon has remained a hurdle for over a decade, restricting the advantages of applying graphene in the growth of III-nitride materials, few previous studies have been conducted. Here, we report the stability of graphene on substrates containing oxygen or nitrogen atoms. Graphene has been observed on highly decomposed Al2O3; however, graphene loss occurred on decomposed AlN at temperatures over 1300 °C. To overcome graphene loss, we investigated 2-D hexagonal boron nitride (h-BN) as an alternative. Unlike graphene on AlN, it was confirmed that h-BN on AlN was intact after the same high-temperature process. Moreover, the overgrown AlN layers on both h-BN/AlN and h-BN/Al2O3could be successfully exfoliated, which indicates that 2-D h-BN survived after AlN growth and underlines its availability for the vdWE/RE of III-nitrides with further mechanical transfer. By enhancing the stability of the 2-D material on the substrate, our study provides insights into the realization of a novel epitaxy concept.

    DOI: 10.1039/d1sc01642c

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  113. Etching-induced damage in heavily Mg-doped p-type GaN and its suppression by low-bias-power inductively coupled plasma-reactive ion etching

    Kumabe Takeru, Ando Yuto, Watanabe Hirotaka, Deki Manato, Tanaka Atsushi, Nitta Shugo, Honda Yoshio, Amano Hiroshi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 60 ( SB ) page: SBBD03   2021.5

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    DOI: 10.35848/1347-4065/abd538

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  114. Impact of heat treatment process on threshold current density in AlGaN-based deep-ultraviolet laser diodes on AlN substrate

    Kushimoto Maki, Zhang Ziyi, Sugiyama Naoharu, Honda Yoshio, Schowalter Leo J., Sasaoka Chiaki, Amano Hiroshi

    APPLIED PHYSICS EXPRESS   Vol. 14 ( 5 ) page: 051003   2021.5

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    DOI: 10.35848/1882-0786/abf443

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  115. Micro-Light Emitting Diode: From Chips to Applications

    Parbrook Peter J., Corbett Brian, Han Jung, Seong Tae-Yeon, Amano Hiroshi

    LASER & PHOTONICS REVIEWS   Vol. 15 ( 5 ) page: 2000133   2021.5

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    DOI: 10.1002/lpor.202000133

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  116. Discrete AlN mole fraction of n/12 (n = 4-8) in Ga-rich zones functioning as electron pathways created in nonflat AlGaN layers grown on high-miscut sapphire substrates

    Y. Nagasawa, A. Hirano, M. Ippommatsu, H. Sako, A. Hashimoto, R. Sugie, Y. Honda, H. Amano, I. Akasaki, K. Kojima, S. F. Chichibu

    Journal of Applied Physics   Vol. 129 ( 16 ) page: 164503   2021.4

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    DOI: 10.1063/5.0042036

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  117. Experimental demonstration of GaN IMPATT diode at X-band

    Kawasaki Seiya, Ando Yuto, Deki Manato, Watanabe Hirotaka, Tanaka Atsushi, Nitta Shugo, Honda Yoshio, Arai Manabu, Amano Hiroshi

    APPLIED PHYSICS EXPRESS   Vol. 14 ( 4 ) page: 046501   2021.4

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    DOI: 10.35848/1882-0786/abe3dc

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  118. Optimization of Ni/Ag-Based Reflectors to Improve the Performance of 273 nm Deep Ultraviolet AlGaN-Based Light Emitting Diodes

    Sim Kee-Baek, Kim Su-Kyung, Lee Hwa-Seub, Lee Sang-Youl, Seong Tae-Yeon, Amano Hiroshi

    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY   Vol. 10 ( 4 ) page: 045005   2021.4

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    DOI: 10.1149/2162-8777/abf49b

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  119. Numerical simulation of ammonothermal crystal growth of GaN-current state, challenges, and prospects

    Crystals   Vol. 11 ( 4 ) page: 356   2021.4

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    DOI: 10.3390/cryst11040356

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  120. Strain-induced yellow to blue emission tailoring of axial InGaN/GaN quantum wells in GaN nanorods synthesized by nanoimprint lithography.

    Avit G, Robin Y, Liao Y, Nan H, Pristovsek M, Amano H

    Scientific reports   Vol. 11 ( 1 ) page: 6754   2021.3

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    DOI: 10.1038/s41598-021-86139-9

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  121. Progress in Modeling Compound Semiconductor Epitaxy: Unintentional Doping in GaN MOVPE

    Kangawa Yoshihiro, Kusaba Akira, Kempisty Pawel, Shiraishi Kenji, Nitta Shugo, Amano Hiroshi

    CRYSTAL GROWTH & DESIGN   Vol. 21 ( 3 ) page: 1878 - 1890   2021.3

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    DOI: 10.1021/acs.cgd.0c01564

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  122. Fabrication of GaN cantilever on GaN substrate by photo-electrochemical etching

    Yamada Takehiro, Ando Yuto, Watanabe Hirotaka, Furusawa Yuta, Tanaka Atsushi, Deki Manato, Nitta Shugo, Honda Yoshio, Suda Jun, Amano Hiroshi

    APPLIED PHYSICS EXPRESS   Vol. 14 ( 3 ) page: 036505   2021.3

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    DOI: 10.35848/1882-0786/abe657

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  123. Boundary Conditions for Simulations of Fluid Flow and Temperature Field during Ammonothermal Crystal Growth-A Machine-Learning Assisted Study of Autoclave Wall Temperature Distribution

    Schimmel Saskia, Tomida Daisuke, Saito Makoto, Bao Quanxi, Ishiguro Toru, Honda Yoshio, Chichibu Shigefusa, Amano Hiroshi

    CRYSTALS   Vol. 11 ( 3 ) page: 1 - 27   2021.3

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    DOI: 10.3390/cryst11030254

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  124. Development of Pulsed TEM Equipped with Nitride Semiconductor Photocathode for High-Speed Observation and Material Nanofabrication

    Yasuda Hidehiro, Nishitani Tomohiro, Ichikawa Shuhei, Hatanaka Shuhei, Honda Yoshio, Amano Hiroshi

    QUANTUM BEAM SCIENCE   Vol. 5 ( 1 ) page: 5   2021.3

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    DOI: 10.3390/qubs5010005

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  125. Suppression of the regrowth interface leakage current in AlGaN/GaN HEMTs by unactivated Mg doped GaN layer

    Liu T., Watanabe H., Nitta S., Wang J., Yu G., Ando Y., Honda Y., Amano H., Tanaka A., Koide Y.

    APPLIED PHYSICS LETTERS   Vol. 118 ( 7 ) page: 072103   2021.2

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    DOI: 10.1063/5.0034584

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  126. Optical properties of neodymium ions in nanoscale regions of gallium nitride (vol 10, pg 2614, 2020)

    Sato Shin-Ichiro, Deki Manato, Watanabe Hirotaka, Nitta Shugo, Honda Yoshio, Nishimura Tomoaki, Gibson Brant C., Greentree Andrew D., Amano Hiroshi, Ohshima Takeshi

    OPTICAL MATERIALS EXPRESS   Vol. 11 ( 2 ) page: 524 - 524   2021.2

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    DOI: 10.1364/OME.420328

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  127. 3D GaN Power Switching Electronics: A Revival of Interest in ELO

    Wang, J; Amano, H; Xie, YH

    2021 5TH IEEE ELECTRON DEVICES TECHNOLOGY & MANUFACTURING CONFERENCE (EDTM)     2021

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    We reported the first-time utilization of ELO (epitaxial lateral overgrowth) GaN (gallium nitride) for power diodes. The undesired stage of coalescence related to ELO is avoided by virtue of a novel 3D device architecture built on the ELO GaN islands on foreign substrate which features pure-lateral p-n and n+ -n-junctions and electrodes lying on the opposing sidewalls of the island. Excellent electrical performance was demonstrated, revealing a strong potential of ELO GaN with 3D device architecture for power switching applications.

    DOI: 10.1109/EDTM50988.2021.9420859

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  128. Generalized Frequency Dependent Small Signal Model for High Frequency Analysis of AlGaN/GaN MOS-HEMTs

    Jadhav A., Ozawa T., Baratov A., Asubar J.T., Kuzuhara M., Wakejima A., Yamashita S., Deki M., Honda Y., Roy S., Amano H., Sarkar B.

    IEEE Journal of the Electron Devices Society   Vol. 9   page: 570 - 581   2021

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    Traditional lumped small signal equivalent circuit models of AlGaN/GaN metal oxide semiconductor high electron mobility transistors (MOS-HEMTs) are made up of constant valued circuit elements. Such models are unable to capture the high frequency behavior (above 20 GHz) of the device. In this work, a modified small signal equivalent circuit model of AlGaN/GaN MOS-HEMTs is presented. The key feature of the proposed model is that the values of the different circuit elements in the model are considered to be frequency dependent in nature and not constants. The frequency dependent value of each circuit element is mathematically represented using polynomial functions where the coefficients of the functions are determined via a least-square curve fitting approach. This frequency dependent attribute of the circuit element values ensures that the proposed model is very accurate at high frequencies without sacrificing the compactness of the model topology. The accuracy of the proposed model has been verified up to 50 GHz using experimentally measured Y-parameters of AlGaN/GaN MOS-HEMTs having a different gate dielectric and gate length.

    DOI: 10.1109/JEDS.2021.3081463

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  129. Development of UV-C laser diodes on AlN substrate

    Kushimoto M.

    Proceedings of SPIE - The International Society for Optical Engineering   Vol. 11686   2021

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    DOI: 10.1117/12.2575872

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  130. Decrease in the injection efficiency and generation of midgap states in UV-C LEDs: A model based on rate equations

    Piva F.

    Proceedings of SPIE - The International Society for Optical Engineering   Vol. 11686   2021

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    DOI: 10.1117/12.2578134

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  131. Electrical properties of GaN metal-insulator-semiconductor field-effect transistors with Al2O3/GaN interfaces formed on vicinal Ga-polar and nonpolar surfaces

    Ando Yuto, Nagamatsu Kentaro, Deki Manato, Taoka Noriyuki, Tanaka Atsushi, Nitta Shugo, Honda Yoshio, Nakamura Tohru, Amano Hiroshi

    APPLIED PHYSICS LETTERS   Vol. 117 ( 24 ) page: 242104   2020.12

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    DOI: 10.1063/5.0028516

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  132. The 2020 UV emitter roadmap

    Amano Hiroshi, Collazo Ramon, Santi Carlo De, Einfeldt Sven, Funato Mitsuru, Glaab Johannes, Hagedorn Sylvia, Hirano Akira, Hirayama Hideki, Ishii Ryota, Kashima Yukio, Kawakami Yoichi, Kirste Ronny, Kneissl Michael, Martin Robert, Mehnke Frank, Meneghini Matteo, Ougazzaden Abdallah, Parbrook Peter J., Rajan Siddharth, Reddy Pramod, Roemer Friedhard, Ruschel Jan, Sarkar Biplab, Scholz Ferdinand, Schowalter Leo J., Shields Philip, Sitar Zlatko, Sulmoni Luca, Wang Tao, Wernicke Tim, Weyers Markus, Witzigmann Bernd, Wu Yuh-Renn, Wunderer Thomas, Zhang Yuewei

    Journal of Physics D: Applied Physics   Vol. 53 ( 50 ) page: 503001   2020.12

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    DOI: 10.1088/1361-6463/aba64c

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  133. Detailed analysis of Ga-rich current pathways created in an n-Al0.7Ga0.3N layer grown on an AlN template with dense macrosteps

    Nagasawa Yosuke, Hirano Akira, Ippommatsu Masamichi, Sako Hideki, Hashimoto Ai, Sugie Ryuichi, Honda Yoshio, Amano Hiroshi, Akasaki Isamu, Kojima Kazunobu, Chichibu Shigefusa F.

    Applied Physics Express   Vol. 13 ( 12 ) page: 124001   2020.12

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    DOI: 10.35848/1882-0786/abcb49

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  134. Surface passivation of light emitting diodes: From nano-size to conventional mesa-etched devices

    Seong Tae-Yeon, Amano Hiroshi

    SURFACES AND INTERFACES   Vol. 21   page: 100765   2020.12

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    DOI: 10.1016/j.surfin.2020.100765

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  135. State-of-the-art and prospects for intense red radiation from core-shell InGaN/GaN nanorods

    Evropeitsev Evgenii A., Kazanov Dmitrii R., Robin Yoann, Smirnov Alexander N., Eliseyev Ilya A., Davydov Valery Yu., Toropov Alexey A., Nitta Shugo, Shubina Tatiana V., Amano Hiroshi

    SCIENTIFIC REPORTS   Vol. 10 ( 1 ) page: 19048   2020.11

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    DOI: 10.1038/s41598-020-76042-0

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  136. Limitation of simple np-n tunnel junction based LEDs grown by metal-organic vapor phase epitaxy

    Robin Y., Bournet Q., Avit G., Pristovsek M., Andre Y., Trassoudaine A., Amano H.

    SEMICONDUCTOR SCIENCE AND TECHNOLOGY   Vol. 35 ( 11 ) page: 115005   2020.11

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    DOI: 10.1088/1361-6641/abad73

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  137. Modeling the degradation mechanisms of AlGaN-based UV-C LEDs: From injection efficiency to mid-gap state generation

    PIVA F.

    Photonics Research   Vol. 8 ( 11 ) page: 1786 - 1791   2020.10

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    DOI: 10.1364/PRJ.401785

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  138. Epitaxial Combination of Two-Dimensional Hexagonal Boron Nitride with Single-Crystalline Diamond Substrate.

    Yang X, Pristovsek M, Nitta S, Liu Y, Honda Y, Koide Y, Kawarada H, Amano H

    ACS applied materials & interfaces   Vol. 12 ( 41 ) page: 46466 - 46475   2020.10

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    DOI: 10.1021/acsami.0c11883

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  139. Space charge profile study of AlGaN-based p-type distributed polarization doped claddings without impurity doping for UV-C laser diodes

    Zhang Ziyi, Kushimoto Maki, Horita Masahiro, Sugiyama Naoharu, Schowalter Leo J., Sasaoka Chiaki, Amano Hiroshi

    APPLIED PHYSICS LETTERS   Vol. 117 ( 15 ) page: 152104   2020.10

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    DOI: 10.1063/5.0027789

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  140. Optical properties of neodymium ions in nanoscale regions of gallium nitride

    Sato S.I.

    Optical Materials Express   Vol. 10 ( 10 ) page: 2614 - 2623   2020.10

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    DOI: 10.1364/OME.401765

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  141. Single-chip imaging system that simultaneously transmits light

    Wang Yongjin, Gao Xumin, Fu Kang, Qin Feifei, Zhu Hongbo, Liu Yuhuai, Amano Hiroshi

    Applied Physics Express   Vol. 13 ( 10 )   2020.10

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    DOI: 10.35848/1882-0786/abb786

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  142. High frequency GaN Devices for Realizing Wirelss Power Transmission System Invited Reviewed

    Hiroshi Amano

    J. IEICE   Vol. 103 ( 10 ) page: 1016 - 1022   2020.10

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    Other Link: https://www.journal.ieice.org/bin/pdf_link.php?fname=k103_10_1016&lang=J&year=2020

  143. Single-chip imaging system that simultaneously transmits light

    Wang, YJ; Gao, XM; Fu, K; Qin, FF; Zhu, HB; Liu, YH; Amano, H

    APPLIED PHYSICS EXPRESS   Vol. 13 ( 10 )   2020.10

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  144. Photoluminescence properties of implanted Praseodymium into Gallium Nitride at elevated temperatures

    Sato S.i.

    Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms   Vol. 479   page: 7 - 12   2020.9

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    DOI: 10.1016/j.nimb.2020.06.007

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  145. Low interface state densities at Al2O3/GaN interfaces formed on vicinal polar and non-polar surfaces

    Ando Yuto, Nagamatsu Kentaro, Deki Manato, Taoka Noriyuki, Tanaka Atsushi, Nitta Shugo, Honda Yoshio, Nakamura Tohru, Amano Hiroshi

    Applied Physics Letters   Vol. 117 ( 10 ) page: 102012   2020.9

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    DOI: 10.1063/5.0010774

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  146. Design and characterization of a low-optical-loss UV-C laser diode

    Zhang Ziyi, Kushimoto Maki, Sakai Tadayoshi, Sugiyama Naoharu, Schowalter Leo J., Sasaoka Chiaki, Amano Hiroshi

    Japanese Journal of Applied Physics   Vol. 59 ( 9 )   2020.9

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    DOI: 10.35848/1347-4065/abaac6

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  147. Design and characterization of a low-optical-loss UV-C laser diode

    Zhang Ziyi, Kushimoto Maki, Sakai Tadayoshi, Sugiyama Naoharu, Schowalter Leo J., Sasaoka Chiaki, Amano Hiroshi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 59 ( 9 )   2020.9

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  148. Increasing the Luminescence Efficiency of Long-Wavelength (In,Ga)N Quantum Well Structures by Electric Field Engineering Using an (Al,Ga)N Capping Layer

    Vichi Stefano, Robin Yoann, Sanguinetti Stefano, Pristovsek Markus, Amano Hiroshi

    PHYSICAL REVIEW APPLIED   Vol. 14 ( 2 ) page: 024018   2020.8

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    DOI: 10.1103/PhysRevApplied.14.024018

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  149. Thermodynamic analysis of the gas phase reaction of Mg-doped GaN growth by HVPE using MgO

    Tomoya Kimura, Kazuki Ohnishi, Yuki Amano, Naoki Fujimoto, Masaaki Araidai, Shugo Nitta, Yoshio Honda, Hiroshi Amano, Yoshihiro Kangawa, Kenji Shiraish

    Japanese Journal of Applied Physics   Vol. 59 ( 8 ) page: 088001   2020.8

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    DOI: 10.35848/1347-4065/aba0d5

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  150. Growth of high-quality GaN by halogen-free vapor phase epitaxy

    Kimura Taishi, Kataoka Keita, Uedono Akira, Amano Hiroshi, Nakamura Daisuke

    Applied Physics Express   Vol. 13 ( 8 ) page: 085509   2020.8

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    DOI: 10.35848/1882-0786/aba494

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  151. Thermodynamic analysis of the gas phase reaction of Mg-doped GaN growth by HVPE using MgO

    Kimura Tomoya, Ohnishi Kazuki, Amano Yuki, Fujimoto Naoki, Araidai Masaaki, Nitta Shugo, Honda Yoshio, Amano Hiroshi, Kangawa Yoshihiro, Shiraishi Kenji

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 59 ( 8 )   2020.8

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  152. Growth of high-quality GaN by halogen-free vapor phase epitaxy

    Kimura Taishi, Kataoka Keita, Uedono Akira, Amano Hiroshi, Nakamura Daisuke

    APPLIED PHYSICS EXPRESS   Vol. 13 ( 8 )   2020.8

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  153. Pulsed-flow growth of polar, semipolar and nonpolar AlGaN

    Dinh Duc V, Hu Nan, Honda Yoshio, Amano Hiroshi, Pristovsek Markus

    JOURNAL OF MATERIALS CHEMISTRY C   Vol. 8 ( 25 ) page: 8668 - 8675   2020.7

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    DOI: 10.1039/d0tc01369b

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  154. Screw dislocation that converts p-type GaN to n-type: Microscopic study on Mg condensation and leakage current in p-n diodes

    T. Nakano, Y. Harashima, K. Chokawa, K. Shiraishi, A. Oshiyama, Y. Kangawa, S. Usami, N. Mayama, K. Toda, A. Tanaka, Y. Honda, H. Amano

    Applied Physics Letters   Vol. 117 ( 1 ) page: 012105   2020.7

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    DOI: 10.1063/5.0010664

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  155. Change of high-voltage conduction mechanism in vertical GaN-on-GaN Schottky diodes at elevated temperatures

    Abhinay Sandupatla, Subramaniam Arulkumaran, Geok Ing Ng, Kumud Ranjan, Manato Deki, Shugo Nitta, Yoshio Honda, Hiroshi Amano

    Applied Physics Express   Vol. 13 ( 7 ) page: 074001   2020.7

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    DOI: 10.35848/1882-0786/ab93a0

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  156. Change of high-voltage conduction mechanism in vertical GaN-on-GaN Schottky diodes at elevated temperatures

    Sandupatla Abhinay, Arulkumaran Subramaniam, Ng Geok Ing, Ranjan Kumud, Deki Manato, Nitta Shugo, Honda Yoshio, Amano Hiroshi

    APPLIED PHYSICS EXPRESS   Vol. 13 ( 7 )   2020.7

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  157. Effect of Annealing on the Electrical and Optical Properties of MgZnO Films Deposited by Radio Frequency Magnetron Sputtering

    Kushimoto Maki, Sakai Tadayoshi, Ueoka Yoshihiro, Tomai Shigekazu, Katsumata Satoshi, Deki Manato, Honda Yoshio, Amano Hiroshi

    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE   Vol. 217 ( 14 ) page: 1900955   2020.7

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    DOI: 10.1002/pssa.201900955

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  158. Lattice bow in thick, homoepitaxial GaN layers for vertical power devices

    Liu Qiang, Fujimoto Naoki, Shen Jian, Nitta Shugo, Tanaka Atsushi, Honda Yoshio, Sitar Zlatko, Bockowski Michal, Kumagai Yoshinao, Amano Hiroshi

    Journal of Crystal Growth   Vol. 539   page: 125643   2020.6

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    DOI: 10.1016/j.jcrysgro.2020.125643

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  159. Halide vapor phase epitaxy of p-Type Mg-doped GaN utilizing MgO

    Ohnishi Kazuki, Amano Yuki, Fujimoto Naoki, Nitta Shugo, Honda Yoshio, Amano Hiroshi

    Applied Physics Express   Vol. 13 ( 6 ) page: 016007   2020.6

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    DOI: 10.35848/1882-0786/ab9166

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  160. Halide vapor phase epitaxy of p-type Mg-doped GaN utilizing MgO

    Ohnishi Kazuki, Amano Yuki, Fujimoto Naoki, Nitta Shugo, Honda Yoshio, Amano Hiroshi

    APPLIED PHYSICS EXPRESS   Vol. 13 ( 6 )   2020.6

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  161. Lattice bow in thick, homoepitaxial GaN layers for vertical power devices

    Liu, Q; Fujimoto, N; Shen, J; Nitta, S; Tanaka, A; Honda, Y; Sitar, Z; Bockowski, M; Kumagai, Y; Amano, H

    JOURNAL OF CRYSTAL GROWTH   Vol. 539   2020.6

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  162. Oxygen Incorporation Kinetics in Vicinal m(10-10) Gallium Nitride Growth by Metal-Organic Vapor Phase Epitaxy

    Yosho Daichi, Shintaku Fumiya, Inatomi Yuya, Kangawa Yoshihiro, Iwata Jun-Ichi, Oshiyama Atsushi, Shiraishi Kenji, Tanaka Atsushi, Amano Hiroshi

    PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS   Vol. 14 ( 6 ) page: 2000142   2020.6

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    DOI: 10.1002/pssr.202000142

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  163. Vertical GaN-on-GaN Schottky Diodes as α-Particle Radiation Sensors.

    Sandupatla A, Arulkumaran S, Ing NG, Nitta S, Kennedy J, Amano H

    Micromachines   Vol. 11 ( 5 ) page: 519   2020.5

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    DOI: 10.3390/mi11050519

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  164. Improving the Leakage Characteristics and Efficiency of GaN-based Micro-Light-Emitting Diode with Optimized Passivation

    Lee Hoon, Lee Jung-Hoon, Park Jin-Seong, Seong Tae-Yeon, Amano Hiroshi

    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY   Vol. 9 ( 5 ) page: 055001   2020.5

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    DOI: 10.1149/2162-8777/ab915d

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  165. Impact of high-Temperature implantation of Mg ions into GaN

    Takahashi Masahiro, Tanaka Atsushi, Ando Yuto, Watanabe Hirotaka, Deki Manato, Kushimoto Maki, Nitta Shugo, Honda Yoshio, Shima Kohei, Kojima Kazunobu, Chichibu Shigefusa F., Amano Hiroshi

    Japanese Journal of Applied Physics   Vol. 59 ( 5 ) page: 056502   2020.5

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    DOI: 10.35848/1347-4065/ab8b3d

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  166. Computational study of oxygen stability in vicinal m(10-10)-GaN growth by MOVPE

    Shintaku Fumiya, Yosho Daichi, Kangawa Yoshihiro, Iwata Jun-Ichi, Oshiyama Atsushi, Shiraishi Kenji, Tanaka Atsushi, Amano Hiroshi

    Applied Physics Express   Vol. 13 ( 5 ) page: 055507   2020.5

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    DOI: 10.35848/1882-0786/ab8723

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  167. Impact of high-temperature implantation of Mg ions into GaN

    Takahashi, M; Tanaka, A; Ando, Y; Watanabe, H; Deki, M; Kushimoto, M; Nitta, S; Honda, Y; Shima, K; Kojima, K; Chichibu, SF; Amano, H

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 59 ( 5 )   2020.5

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  168. Computational study of oxygen stability in vicinal m(10-10)-GaN growth by MOVPE

    Shintaku Fumiya, Yosho Daichi, Kangawa Yoshihiro, Iwata Jun-Ichi, Oshiyama Atsushi, Shiraishi Kenji, Tanaka Atsushi, Amano Hiroshi

    APPLIED PHYSICS EXPRESS   Vol. 13 ( 5 )   2020.5

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  169. Improved Leakage and Output Characteristics of Pixelated LED Array for Headlight application

    Lee Sang-Youl, Kang Kiman, Lee Eunduk, Jo Yoomin, Kim Doyub, Oh Jeong-Tak, Jeong Hwan-Hee, Seong Tae-Yeon, Amano Hiroshi

    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY   Vol. 9 ( 4 ) page: 045011   2020.4

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    DOI: 10.1149/2162-8777/ab8b6f

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  170. Experimental observation of high intrinsic thermal conductivity of AlN

    Cheng Zhe, Koh Yee Rui, Mamun Abdullah, Shi Jingjing, Bai Tingyu, Huynh Kenny, Yates Luke, Liu Zeyu, Li Ruiyang, Lee Eungkyu, Liao Michael E., Wang Yekan, Yu Hsuan Ming, Kushimoto Maki, Luo Tengfei, Goorsky Mark S., Hopkins Patrick E., Amano Hiroshi, Khan Asif, Graham Samuel

    PHYSICAL REVIEW MATERIALS   Vol. 4 ( 4 ) page: 044602   2020.4

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    DOI: 10.1103/PhysRevMaterials.4.044602

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  171. Tungsten carbide layers deposited on graphite substrates via a wet powder process as anti-parasitic-reaction coatings for reactor components in GaN growth

    Nakamura Daisuke, Kimura Taishi, Itoh Kenji, Fujimoto Naoki, Nitta Shugo, Amano Hiroshi

    CRYSTENGCOMM   Vol. 22 ( 15 ) page: 2632 - 2641   2020.4

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    DOI: 10.1039/c9ce01971e

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  172. Improved Light Output of AlGaInP-Based Micro-Light Emitting Diode Using Distributed Bragg Reflector

    Lee Sang-Youl, Moon Ji Hyung, Moon Yong-Tae, Kim Chung Song, Park Sunwoo, Oh Jeong-Tak, Jeong Hwan-Hee, Seong Tae-Yeon, Amano Hiroshi

    IEEE PHOTONICS TECHNOLOGY LETTERS   Vol. 32 ( 7 ) page: 438 - 441   2020.4

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    DOI: 10.1109/LPT.2020.2977376

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  173. Scalable fabrication of GaN on amorphous substrates via MOCVD on highly oriented silicon seed layers

    Hainey Mel Jr., Robin Yoann, Avit Geoffrey, Amano Hiroshi, Usami Noritaka

    JOURNAL OF CRYSTAL GROWTH   Vol. 535   page: 125522   2020.4

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    DOI: 10.1016/j.jcrysgro.2020.125522

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  174. Demonstration of Observation of Dislocations in GaN by Novel Birefringence Method

    Tanaka Atsushi, Inotsume Syo, Harada Shunta, Hanada Kenji, Honda Yoshio, Ujihara Toru, Amano Hiroshi

    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS   Vol. 257 ( 4 ) page: 1900553   2020.4

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    DOI: 10.1002/pssb.201900553

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  175. On-wafer fabrication of etched-mirror UV-C laser diodes with the ALD-deposited DBR

    Sakai Tadayoshi, Kushimoto Maki, Zhang Ziyi, Sugiyama Naoharu, Schowalter Leo J., Honda Yoshio, Sasaoka Chiaki, Amano Hiroshi

    APPLIED PHYSICS LETTERS   Vol. 116 ( 12 ) page: 122101   2020.3

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    DOI: 10.1063/1.5145017

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  176. Effects of Ultraviolet Wavelength and Ambient Temperature on Reliability of Silicones in InAlGaN-Based Light-Emitting-Diode Package

    Kim Ho-Young, Lee Jong-Woo, Jun Duk-Jin, Song Sung-Joo, Oh Jeong-Tak, Jeong Hwan-Hee, Seong Tae-Yeon, Amano Hiroshi

    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY   Vol. 9 ( 3 ) page: 035005   2020.3

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    DOI: 10.1149/2162-8777/ab7c40

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  177. Visualization of different carrier concentrations in n-type-GaN semiconductors by phase-shifting electron holography with multiple electron biprisms.

    Yamamoto K, Nakano K, Tanaka A, Honda Y, Ando Y, Ogura M, Matsumoto M, Anada S, Ishikawa Y, Amano H, Hirayama T

    Microscopy (Oxford, England)   Vol. 69 ( 1 ) page: 1-10   2020.3

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    DOI: 10.1093/jmicro/dfz037

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  178. Using SiO2-Based Distributed Bragg Reflector to Improve the Performance of AlGaInP-Based Red Micro-Light Emitting Diode

    Lee Sang-Youl, Moon Ji Hyung, Moon Yong-Tae, Choi Byoungjun, Oh Jeong-Tak, Jeong Hwan-Hee, Seong Tae-Yeon, Amano Hiroshi

    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY   Vol. 9 ( 3 ) page: 036002   2020.2

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    DOI: 10.1149/2162-8777/ab74c3

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  179. Using SiO<inf>2</inf>-based distributed Bragg reflector to improve the performance of AlGaInP-based red micro-light emitting diode

    Lee S.Y., Moon J.H., Moon Y.T., Choi B., Oh J.T., Jeong H.H., Seong T.Y., Amano H.

    ECS Journal of Solid State Science and Technology   Vol. 9 ( 3 )   2020.2

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    We have investigated how different types of the reflectors affected the optical and electrical performance of AlGaInP-based micro-LEDs. Simulations showed that the AlGaAs-based epitaxial distributed Bragg reflector (DBR) had a stopband at the 610–624 nm region with reflectivity of 90%, the SiO2/TiO2 dielectric DBR gave a stopband at the 580–770 nm range with a maximum reflectivity of 99%, and the ITO/Ag metal reflector exhibited reflectivity of 90% across the 400–800 nm region. All micro-LEDs gave forward voltages of 1.895–1.960 V at 20 μA. The micro-LEDs with the dielectric DBR and metal reflector yielded 31% and 13% higher light output at 20 μA than that with the epitaxial DBR, respectively. All of the micro-LEDs contained a shoulder peak at approximately 615 nm in their electroluminescence spectra. Ray-tracing simulations exhibited that the micro-LEDs with the dielectric DBR and metal reflector produced 26% and 22% higher total light output power than the one with the epitaxial DBR, respectively. It was also shown that for the micro-LEDs with the metal reflector, some of the micro-LEDs were detached from the metal reflectors due to the interfacial voids induced as a result of agglomeration of Ag layer during fabrication process.

    DOI: 10.1149/2162-8777/ab74c3/pdf

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  180. Optimization of InGaN thickness for high-quantum-efficiency Cs/O-activated InGaN photocathode

    Sato Daiki, Honda Anna, Koizumi Atsushi, Nishitani Tomohiro, Honda Yoshio, Amano Hiroshi

    MICROELECTRONIC ENGINEERING   Vol. 223   page: 111229   2020.2

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    DOI: 10.1016/j.mee.2020.111229

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  181. Effect of unevenly-distributed V pits on the optical and electrical characteristics of green micro-light emitting diode

    Lee Da-Hoon, Kang Daesung, Seong Tae-Yeon, Kneissl Michael, Amano Hiroshi

    JOURNAL OF PHYSICS D-APPLIED PHYSICS   Vol. 53 ( 4 ) page: 045106   2020.1

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    DOI: 10.1088/1361-6463/ab52d0

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  182. Oblique-Angle Deposited SiO2/Al Omnidirectional Reflector for Enhancing the Performance of AlGaN-Based Ultraviolet Light-Emitting Diod

    Jeongwon Lee, Tae-Yeon Seong, Hiroshi Amano

    ECS Journal of Solid State Science and Technology   Vol. 9 ( 2 )   2020.1

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    DOI: 10.1149/2162-8777/ab709a

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  183. Oblique-Angle Deposited SiO2/Al Omnidirectional Reflector for Enhancing the Performance of AlGaN-Based Ultraviolet Light-Emitting Diode

    Jeongwon Lee, Tae-Yeon Seong, Hiroshi Amano

    ECS Journal of Solid State Science and Technology   Vol. 9 ( 2 ) page: 026005   2020.1

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    DOI: 10.1149/2162-8777/ab709a

  184. Heavy Mg Doping to Form Reliable Rh Reflective Ohmic Contact for 278 nm Deep Ultraviolet AlGaN-Based Light-Emitting Diodes

    Lee Sang-Youl, Han Dae-Seob, Lee Yong-Gyeong, Choi Kwang-Ki, Oh Jeong-Tak, Jeong Hwan-Hee, Seong Tae-Yeon, Amano Hiroshi

    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY   Vol. 9 ( 6 ) page: 065016   2020.1

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    DOI: 10.1149/2162-8777/aba914

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  185. Improved breakdown voltage in vertical GaN Schottky barrier diodes on free-standing GaN with Mg-compensated drift layer

    Abhinay S., Arulkumaran S., Ng G. I., Ranjan K., Deki M., Nitta S., Honda Y., Amano H.

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 59 ( 1 ) page: 010906   2020.1

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    DOI: 10.7567/1347-4065/ab65cd

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  186. Recovery of quantum efficiency on Cs/O-activated GaN and GaAs photocathodes by thermal annealing in vacuum

    Daiki Sato, Tomohiro Nishitani, Yoshio Honda, Hiroshi Amano

    Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics   Vol. 38 ( 1 ) page: 012603   2020.1

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    DOI: 10.1116/1.5120417

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  187. Scalable synthesis of multilayer h-BN on AlN by metalorganic vapor phase epitaxy: nucleation and growth mechanism

    Yang Xu, Nitta Shugo, Pristovsek Markus, Liu Yuhuai, Liao Yaqiang, Kushimoto Maki, Honda Yoshio, Amano Hiroshi

    2D MATERIALS   Vol. 7 ( 1 ) page: 015004   2020.1

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    DOI: 10.1088/2053-1583/ab46e6

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  188. Analysis of trimethylgallium decomposition by high-resolution mass spectrometry

    Zheng Ye, Shugo Nitta, Yoshio Honda, Markus Pristovsek, Hiroshi Amano

    Japanese Journal of Applied Physics   Vol. 59 ( 2 ) page: 025511   2020

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.35848/1347-4065/ab6fb0

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  189. Preface-JSS Focus Issue on Recent Advances inWide Bandgap III-Nitride Devices and Solid State Lighting: A Tribute to Isamu Akasaki

    Ren Fan, Mishra Kailash C., Amano Hiroshi, Collins John, Han Jung, Im Won Bin, Kneissl Michael, Seong Tae-Yeon, Setlur Anant, Suski Tadek, Zych Eugeniusz

    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY   Vol. 9 ( 1 ) page: 010001   2020

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    DOI: 10.1149/2.0452001JSS

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  190. Indium incorporation and optical properties of polar, semipolar and nonpolar InAlN

    Duc V Dinh, Nan Hu, Yoshio Honda, Hiroshi Amano, Markus Pristovsek

    Semiconductor Science and Technology   Vol. 35 ( 3 ) page: 035004   2020

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    DOI: 10.1088/1361-6641/ab63f1

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  191. Damage-Free Plasma Etching to Enhance Performance of AlGaInP-Based Micro-Light Emitting Diode

    Lee Sang-Youl, Lee Eunduk, Moon Ji-Hyung, Choi Byoungjun, Oh Jeong-Tak, Jeong Hwan-Hee, Seong Tae-Yeon, Amano Hiroshi

    IEEE PHOTONICS TECHNOLOGY LETTERS   Vol. 32 ( 17 ) page: 1041 - 1044   2020

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    DOI: 10.1109/LPT.2020.3010820

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  192. Characterization of AlGaN multiple-quantum-wells grown on <i>c</i>-plane AlN/sapphire templates with macro-steps

    Kojima Kazunobu, Nagasawa Yosuke, Hirano Akira, Ippommatsu Masamichi, Sugie Ryuichi, Honda Yoshio, Amano Hiroshi, Akasaki Isamu, Chichibu Shigefusa F.

    Journal of the Japanese Association for Crystal Growth   Vol. 47 ( 3 ) page: n/a   2020

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    <p>  The microscopic structural and optical characteristics of AlGaN light-emitting diodes (LEDs) fabricated on the AlN templates with dense macrosteps are shown to clarify the origin of their high internal quantum efficiency of radiation (IQE). The cross-sectional transmission electron microscopy observations under the high-angle annular dark field scanning mode and microscopic energy dispersive X-ray spectroscopy revealed that the AlGaN cladding layer under the AlGaN quantum well (QW) layer had a microscopic compositional modulation, which originates from the macrosteps at the AlN template surface. Moreover, Ga-rich portions in the cladding layer behaved as current micropaths, and the micropaths are connected with the carrier localization structure formed in QWs. The in-plane cathodoluminescence (CL) spectroscopy showed a significant inhomogeneity of the CL characteristics. The gentle slopes at the sample surface showed brighter emissions with a lower peak photon energy, confirming the carrier localization. This carrier localization structure in the QWs combined with the current micropaths in the cladding layer can increase the IQE as well as external quantum efficiency of the AlGaN LEDs.</p>

    DOI: 10.19009/jjacg.47-3-04

    CiNii Research

  193. Dielectric Ruduced Surface Field Effect on Vertical GaN-on-GaN Nanowire Schottky Barrier Diodes

    PROCEEDINGS OF THE 2020 32ND INTERNATIONAL SYMPOSIUM ON POWER SEMICONDUCTOR DEVICES AND ICS (ISPSD 2020)   Vol. 2020-September   page: 349 - 352   2020

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    DOI: 10.1109/ispsd46842.2020.9170101

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  194. Role of defects in the mid-term degradation of UV-B LEDs investigated by optical and DLTS measurements

    Piva F., De Santi C., Deki M., Kushimoto M., Amano H., Tomozawa H., Shibata N., Meneghesso G., Zanoni E., Meneghini M.

    GALLIUM NITRIDE MATERIALS AND DEVICES XV   Vol. 11280   page: 1128015   2020

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    DOI: 10.1117/12.2544704

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  195. Low leakage Mg-compensated GaN Schottky diodes on free-standing GaN substrate for high energy alpha-particle detection

    Sandupatia A., Arulkurnaran S., Ranjan K., Ng G. I, Murumu P. P., Kennedy J., Deki M., Nitta S., Honda Y., Amano H.

    2020 IEEE ELECTRON DEVICES TECHNOLOGY AND MANUFACTURING CONFERENCE (EDTM 2020)     2020

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  196. Development of laser slicing technology for GaN substrates

    KAWAGUCHI Daisuke, TANAKA Atsushi, YUI Toshiki, IGASAKI Yasunori, WANI Yotaro, AMANO Hiroshi

    The Proceedings of Mechanical Engineering Congress, Japan   Vol. 2020 ( 0 ) page: S16306   2020

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    DOI: 10.1299/jsmemecj.2020.s16306

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  197. UV-C Laser Diodes Fabricated on High Quality AlN Substrate

    SASAOKA Chiaki, AMANO Hiroshi

    The Review of Laser Engineering   Vol. 48 ( 8 ) page: 427   2020

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    A UV-C laser diode is a promising light source for processing and machining applications due to photon
    energy near 5 eV. Recently, our group reported a 272-nm laser diode (LD) fabricated on a high-quality
    AlN substrate. Several key technologies are involved to achieve lasing; a low-dislocation-density AlN
    substrate to reduce waveguide optical loss, and distributed polarization doping to increase the hole density
    in the p-side AlGaN cladding of high Al composition. After introducing these key technologies, we
    describe a highly productive on-wafer laser fabrication process in which a facet mirror is prepared by
    dry- and wet-etching and coated with atomic layer deposited DBR (Distributed Bragg Reflector). These
    technologies are expected to open up new UV-C applications and be widely implemented around the
    world.

    DOI: 10.2184/lsj.48.8_427

    CiNii Research

  198. Improvement of The Light Output of Blue InGaN-Based Light Emitting Diodes by Using a Buried Stripe -Type n-Contact and Reflective Bonding Pad

    Kim Jong-Ho, Lee Yong Won, Im Hyeong-Seop, Oh Chan-Hyoung, Shim Jong-In, Kang Daesung, Seong Tae-Yeon, Amano Hiroshi

    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY   Vol. 9 ( 1 ) page: 015021   2019.12

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    DOI: 10.1149/2.0462001JSS

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  199. Two-dimensional analysis of the nonuniform quantum yields of multiple quantum wells for AlGaN-based deep-ultraviolet LEDs grown on AlN templates with dense macrosteps using cathodoluminescence spectroscopy

    Nagasawa Yosuke, Sugie Ryuichi, Kojima Kazunobu, Hirano Akira, Ippommatsu Masamichi, Honda Yoshio, Amano Hiroshi, Akasaki Isamu, Chichibu Shigefusa F.

    JOURNAL OF APPLIED PHYSICS   Vol. 126 ( 21 ) page: 215703   2019.12

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    DOI: 10.1063/1.5125623

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  200. Suppression of Green Luminescence of Mg-Ion-Implanted GaN by Subsequent Implantation of Fluorine Ions at High Temperature

    Takahashi Masahiro, Tanaka Atsushi, Ando Yuto, Watanabe Hirotaka, Deki Manato, Kushimoto Maki, Nitta Shugo, Honda Yoshio, Shima Kohei, Kojima Kazunobu, Chichibu Shigefusa F., Chen Kevin J., Amano Hiroshi

    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS   Vol. 257   page: 1900554   2019.12

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    DOI: 10.1002/pssb.201900554

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  201. A 271.8 nm deep-ultraviolet laser diode for room temperature operation

    Zhang Ziyi, Kushimoto Maki, Sakai Tadayoshi, Sugiyama Naoharu, Schowalter Leo J., Sasaoka Chiaki, Amano Hiroshi

    APPLIED PHYSICS EXPRESS   Vol. 12 ( 12 ) page: 124003   2019.12

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    DOI: 10.7567/1882-0786/ab50e0

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  202. Untwinned semipolar (10(1)over-bar3) AlxGa1-xN layers grown on m-plane sapphire

    Dinh Duc V., Hu Nan, Amano Hiroshi, Honda Yoshio, Pristovsek Markus

    SEMICONDUCTOR SCIENCE AND TECHNOLOGY   Vol. 34 ( 12 ) page: 125012   2019.12

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    DOI: 10.1088/1361-6641/ab4d2c

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  203. Low Voltage High-Energy alpha-Particle Detectors by GaN-on-GaN Schottky Diodes with Record-High Charge Collection Efficiency

    Sandupatla Abhinay, Arulkumaran Subramaniam, Ranjan Kumud, Ng Geok Ing, Murmu Peter P., Kennedy John, Nitta Shugo, Honda Yoshio, Deki Manato, Amano Hiroshi

    SENSORS   Vol. 19 ( 23 ) page: 5107   2019.12

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    DOI: 10.3390/s19235107

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    PubMed

  204. Improvement in the Reliability of AlGaInP-Based Light-Emitting Diode Package Using Optimal Silicone and Leadframe Structure

    Kim Ho-Young, Lee Jong Woo, Moon Young Min, Oh Jeong Tak, Jeong Hwan-Hee, Song June-O, Seong Tae-Yeon, Kneissl Michael, Amano Hiroshi

    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY   Vol. 9 ( 1 ) page: 015014   2019.11

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    DOI: 10.1149/2.0332001JSS

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  205. Aluminium incorporation in polar, semi- and non-polar AlGaN layers: a comparative study of x-ray diffraction and optical properties

    Duc V Dinh, Hu Nan, Honda Yoshio, Amano Hiroshi, Pristovsek Markus

    SCIENTIFIC REPORTS   Vol. 9   page: 15802   2019.11

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    DOI: 10.1038/s41598-019-52067-y

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  206. Hole injection mechanism in the quantum wells of blue light emitting diode with V pits for micro-display application

    Kang Daesung, Oh Jeong-Tak, Song June-O, Seong Tae-Yeon, Kneissl Michael, Amano Hiroshi

    APPLIED PHYSICS EXPRESS   Vol. 12 ( 10 ) page: 102016   2019.10

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    DOI: 10.7567/1882-0786/ab45d1

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  207. V-shaped dislocations in a GaN epitaxial layer on GaN substrate

    Tanaka Atsushi, Nagamatsu Kentaro, Usami Shigeyoshi, Kushimoto Maki, Deki Manato, Nitta Shugo, Honda Yoshio, Bockowski Michal, Amano Hiroshi

    AIP ADVANCES   Vol. 9 ( 9 ) page: 095002   2019.9

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    DOI: 10.1063/1.5114866

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  208. Stability and degradation of AlGaN-based UV-B LEDs: Role of doping and semiconductor defects

    Piva F., De Santi C., Deki M., Kushimoto M., Amano H., Tomozawa H., Shibata N., Meneghesso G., Zanoni E., Meneghini M.

    MICROELECTRONICS RELIABILITY   Vol. 100-101   page: 113418   2019.9

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    DOI: 10.1016/j.microrel.2019.113418

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  209. Via-Hole-Type Flip-Chip Packaging to Improve the Thermal Characteristics and Reliability of Blue Light Emitting Diodes

    Kim Ho Young, Lim Chang Man, Kim Ki Seok, Oh Jeong Tak, Jeong Hwan-Hee, Song June-O, Seong Tae-Yeon, Amano Hiroshi

    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY   Vol. 8 ( 9 ) page: Q165 - Q170   2019.8

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    DOI: 10.1149/2.0171909jss

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  210. Combined effects of V pits and chip size on the electrical and optical properties of green InGaN-based light-emitting diodes

    Kim Dae-Hyun, Park Young Soo, Kang Daesung, Kim Kyoung-Kook, Seong Tae-Yeon, Amano Hiroshi

    JOURNAL OF ALLOYS AND COMPOUNDS   Vol. 796   page: 146-152   2019.8

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    DOI: 10.1016/j.jallcom.2019.05.070

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  211. Indium Incorporation into InGaN Quantum Wells Grown on GaN Narrow Stripes

    Sarzynski Marcin, Grzanka Ewa, Grzanka Szymon, Targowski Grzegorz, Czernecki Robert, Reszka Anna, Holy Vaclav, Nitta Shugo, Liu Zhibin, Amano Hiroshi, Leszczynski Mike

    MATERIALS   Vol. 12 ( 16 ) page: 2583   2019.8

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    DOI: 10.3390/ma12162583

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  212. Influence of Temperature-Dependent Substrate Decomposition on Graphene for Separable GaN Growth

    Park Jeong-Hwan, Lee Jun-Yeob, Park Mun-Do, Min Jung-Hong, Lee Je-Sung, Yang Xu, Kang Seokjin, Kim Sang-Jo, Jeong Woo-Lim, Amano Hiroshi, Lee Dong-Seon

    ADVANCED MATERIALS INTERFACES   Vol. 6   page: 1900821   2019.7

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    DOI: 10.1002/admi.201900821

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  213. Fabrication of a GaInN/GaInP/GaInAs/Ge four-junction solar cell using the wafer bonding technology

    Takahashi Kazuya, Shinoda Ryoji, Mitsufuji Syun, Iwaya Motoaki, Kamiyama Satoshi, Takeuchi Tetsuya, Hattori Tomokazu, Akasaki Isamu, Amano Hiroshi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 58 ( 7 ) page: 072003   2019.7

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    DOI: 10.7567/1347-4065/ab26ad

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  214. Origin of acceptor diffusion into silicon substrate during GaN growth by metal organic chemical vapor deposition

    Matsumoto Koji, Ono Toshiaki, Honda Yoshio, Torigoe Kazuhisa, Kushimoto Maki, Amano Hiroshi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 58 ( 7 ) page: 075502   2019.7

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    DOI: 10.7567/1347-4065/ab2657

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  215. Ammonia decomposition and reaction by high-resolution mass spectrometry for group III - Nitride epitaxial growth

    Ye Zheng, Nitta Shugo, Nagamatsu Kentaro, Fujimoto Naoki, Kushimoto Maki, Deki Manato, Tanaka Atsushi, Honda Yoshio, Pristovsek Markus, Amano Hiroshi

    JOURNAL OF CRYSTAL GROWTH   Vol. 516   page: 63-66   2019.6

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    DOI: 10.1016/j.jcrysgro.2019.03.025

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  216. Direct evidence of Mg diffusion through threading mixed dislocations in GaN p-n diodes and its effect on reverse leakage current

    Usami Shigeyoshi, Mayama Norihito, Toda Kazuya, Tanaka Atsushi, Deki Manato, Nitta Shugo, Honda Yoshio, Amano Hiroshi

    APPLIED PHYSICS LETTERS   Vol. 114 ( 23 ) page: 232105   2019.6

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    DOI: 10.1063/1.5097767

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  217. Computational fluid dynamics simulation study of the gas flow balance in a vertical HVPE reactor with a showerhead for low cost bulk GaN crystal growth

    Liu Qiang, Fujimoto Naoki, Nitta Shugo, Honda Yoshio, Amano Hiroshi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 58 ( SC ) page: SC1055   2019.6

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    DOI: 10.7567/1347-4065/ab124e

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  218. Monolithic integration of tricolor micro-LEDs and color mixing investigation by analog and digital dimming

    Robin Yoann, Hemeret Francois, D'Inca Gillian, Pristovsek Markus, Trassoudaine Agnes, Amano Hiroshi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 58 ( SC ) page: SCCC06   2019.6

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    DOI: 10.7567/1347-4065/ab06ae

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  219. Effect of photoelectrochemical etching and post-metallization annealing on gate controllability of AlGaN/GaN high electron mobility transistors

    Uemura Keisuke, Deki Manato, Honda Yoshio, Amano Hiroshi, Sato Taketomo

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 58 ( SC ) page: SCCD20   2019.6

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    DOI: 10.7567/1347-4065/ab06b9

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  220. Deeply and vertically etched butte structure of vertical GaN p-n diode with avalanche capability

    Fukushima Hayata, Usami Shigeyoshi, Ogura Masaya, Ando Yuto, Tanaka Atsushi, Deki Manato, Kushimoto Maki, Nitta Shugo, Honda Yoshio, Amano Hiroshi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 58 ( SC ) page: SCCD25   2019.6

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    DOI: 10.7567/1347-4065/ab106c

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  221. Correlation between nanopipes formed from screw dislocations during homoepitaxial growth by metal-organic vapor-phase epitaxy and reverse leakage current in vertical p-n diodes on a free-standing GaN substrates

    Usami Shigeyoshi, Tanaka Atsushi, Fukushima Hayata, Ando Yuto, Deki Manato, Nitta Shugo, Honda Yoshio, Amano Hiroshi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 58 ( SC ) page: SCCB24   2019.6

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    DOI: 10.7567/1347-4065/ab1250

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  222. Controlling the orientations of directional sputtered non- and semi-polar GaN/AlN layers

    Nan Hu, Dinh Duc V., Pristovsek Markus, Honda Yoshio, Amano Hiroshi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 58 ( SC ) page: SC1044   2019.6

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    DOI: 10.7567/1347-4065/ab1252

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  223. Comparison of AlxGa1-xN multiple quantum wells designed for 265 and 285nm deep-ultraviolet LEDs grown on AlN templates having macrosteps

    Nagasawa Yosuke, Kojima Kazunobu, Hirano Akira, Ipponmatsu Masamichi, Honda Yoshio, Amano Hiroshi, Akasaki Isamu, Chichibu Shigefusa F.

    APPLIED PHYSICS EXPRESS   Vol. 12 ( 6 ) page: 064009   2019.6

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    DOI: 10.7567/1882-0786/ab21a9

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  224. Narrow Excitonic Lines in Core-Shell Nanorods With InGaN/GaN Quantum Wells Intersected by Basal Stacking Faults

    Evropeitsev Evgeniy A., Robin Yoann, Shubina Tatiana V., Bae Si-Young, Nitta Shugo, Kirilenko Demid A., Davydov Valery Y., Smirnov Alexandr N., Toropov Alexey A., Kushimoto Maki, Ivanov Sergey V., Amano Hiroshi

    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS   Vol. 256 ( 6 ) page: 1800648   2019.6

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    DOI: 10.1002/pssb.201800648

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  225. Morphological study of InGaN on GaN substrate by supersaturation (vol 508, pg 58, 2019)

    Liu Zhibin, Nitta Shugo, Robin Yoann, Kushimoto Maki, Deki Manato, Honda Yoshio, Pristovsek Markus, Sitar Zlatko, Amano Hiroshi

    JOURNAL OF CRYSTAL GROWTH   Vol. 514   page: 13-13   2019.5

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    DOI: 10.1016/j.jcrysgro.2019.02.058

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  226. Effect of substrate misorientation on the concentration of impurities and surface morphology of an epitaxial GaN layer on N-polar GaN substrate by MOVPE

    Nagamatsu Kentaro, Ando Yuto, Kono Tsukasa, Cheong Heajeong, Nitta Shugo, Honda Yoshio, Pristovsek Markus, Amano Hiroshi

    JOURNAL OF CRYSTAL GROWTH   Vol. 512   page: 78-83   2019.4

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    DOI: 10.1016/j.jcrysgro.2019.02.013

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  227. Nonpolar m-plane AlxGa1-xN layers grown on m-plane sapphire by MOVPE

    Duc V Dinh, Amano Hiroshi, Pristovsek Markus

    JOURNAL OF CRYSTAL GROWTH   Vol. 512   page: 100-104   2019.4

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    DOI: 10.1016/j.jcrysgro.2019.02.020

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  228. The emergence and prospects of deep-ultraviolet light-emitting diode technologies

    Kneissl Michael, Seong Tae-Yeon, Han Jung, Amano Hiroshi

    NATURE PHOTONICS   Vol. 13 ( 4 ) page: 233-244   2019.4

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    DOI: 10.1038/s41566-019-0359-9

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  229. GaN drift-layer thickness effects in vertical Schottky barrier diodes on free-standing HVPE GaN substrates

    Sandupatla A., Arulkumaran S., Ng G. I., Ranjan K., Deki M., Nitta S., Honda Y., Amano H.

    AIP ADVANCES   Vol. 9 ( 4 ) page: 045007   2019.4

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    DOI: 10.1063/1.5087491

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  230. Transfer-free fabrication of a graphene transparent electrode on a GaN-based light-emitting diode using the direct precipitation method

    Yamada Jumpei, Usami Shigeyoshi, Ueda Yuki, Honda Yoshio, Amano Hiroshi, Maruyama Takahiro, Naritsuka Shigeya

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 58 ( 4 ) page: 040904   2019.4

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    DOI: 10.7567/1347-4065/aafe70

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  231. Effect of gas phase temperature on InGaN grown by metalorganic vapor phase epitaxy

    Liu Zhibin, Nitta Shugo, Usami Shigeyoshi, Robin Yoann, Kushimoto Maki, Deki Manato, Honda Yoshio, Pristovsek Markus, Amano Hiroshi

    JOURNAL OF CRYSTAL GROWTH   Vol. 509   page: 50-53   2019.3

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    DOI: 10.1016/j.jcrysgro.2018.12.007

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  232. GaN-on-Si resonant-cavity light-emitting diode incorporating top and bottom dielectric distributed Bragg reflectors

    Cai Wei, Yuan Jialei, Ni Shuyu, Shi Zheng, Zhou Weidong, Liu Yuhuai, Wang Yongjin, Amano Hiroshi

    APPLIED PHYSICS EXPRESS   Vol. 12 ( 3 ) page: 032004   2019.3

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    DOI: 10.7567/1882-0786/ab023c

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  233. Fully Ion Implanted Normally-Off GaN DMOSFETs with ALD-Al2O3 Gate Dielectrics

    Yoshino Michitaka, Ando Yuto, Deki Manato, Toyabe Toru, Kuriyama Kazuo, Honda Yoshio, Nishimura Tomoaki, Amano Hiroshi, Kachi Tetsu, Nakamura Tohru

    MATERIALS   Vol. 12 ( 5 ) page: 689   2019.3

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    DOI: 10.3390/ma12050689

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  234. Effects of Drift Layer Thicknesses in Reverse Conduction Mechanism on Vertical GaN-on-GaN SBDs grown by MOCVD

    Abhinay S., Arulkumaran S., Ng G.I., Ranjan K., Deki M., Nitta S., Honda Y., Amano H.

    2019 Electron Devices Technology and Manufacturing Conference, EDTM 2019     page: 106 - 108   2019.3

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    Effect of drift layer thicknesses (DLT) (2, 15 and 30 μm) in reverse current conduction mechanisms of vertical GaN-on-GaN Schottky Barrier Diodes grown MOCVD has been investigated for the first time. The conduction mechanism is changing from thermionic field emission (TFE) to thermionic emission (TE) when the DLT of GaN increases. The SBDs with DLT of 2 μm and 30 μm exhibit TFE through Poole-Frenkel emission and TE, respectively. However, the SBDs with DLT of 15 μm exhibit both TFE and TE. Activation energy (Ea) of traps was also calculated to be 0.69 eV for 2 μm, 0.38 for 15 μm and 0.4 eV for 30 μm respectively. Ea of 0.69 eV and 0.4 eV could be associated with screw threading dislocations and the presence of Mg in the grown drift layer, respectively.

    DOI: 10.1109/EDTM.2019.8731215

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  235. Electronic structure analysis at threading dislocation and at m-plane surface of nanopipes in GaN thin films

    Nakano Takashi, Chokawa Kenta, Araidai Masaaki, Shiraishi Kenji, Oshiyama Atsushi, Usami Shigeyoshi, Kusaba Akira, Kangawa Yoshihiro, Tanaka Atsushi, Honda Yoshio, Amano Hiroshi

    JSAP Annual Meetings Extended Abstracts   Vol. 2019.1 ( 0 ) page: 3122 - 3122   2019.2

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    DOI: 10.11470/jsapmeeting.2019.1.0_3122

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  236. Morphological study of InGaN on GaN substrate by supersaturation

    Liu Zhibin, Nitta Shugo, Robin Yoann, Kushimoto Maki, Deki Manato, Honda Yoshio, Pristovsek Markus, Amano Hiroshi

    JOURNAL OF CRYSTAL GROWTH   Vol. 508   page: 58-65   2019.2

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    DOI: 10.1016/j.jcrysgro.2018.12.028

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  237. How to obtain metal-polar untwinned high-quality (10-13) GaN on m-plane sapphire

    Hu Nan, Dinh Duc V., Pristovsek Markus, Honda Yoshio, Amano Hiroshi

    JOURNAL OF CRYSTAL GROWTH   Vol. 507   page: 205 - 208   2019.2

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    DOI: 10.1016/j.jcrysgro.2018.11.013

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  238. Observation of Dopant Concentration in GaN Semiconductor by High Sensitivity Electron Holography

    Nakano Kiyotaka, Matsumoto Miko, Anada Satoshi, Yamamoto Kazuo, Ishikawa Yukari, Hirayama Tsukasa, Ando Yuto, Ogura Masaya, Tanaka Atsushi, Honda Yoshio, Amano Hiroshi

    Materia Japan   Vol. 58 ( 2 ) page: 103 - 103   2019.2

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    DOI: 10.2320/materia.58.103

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  239. Pole figure analysis from electron backscatter diffraction-an effective method of evaluating fiber-textured silicon thin films as seed layers for epitaxy

    Hainey Mel Jr., Robin Yoann, Amano Hiroshi, Usami Noritaka

    APPLIED PHYSICS EXPRESS   Vol. 12 ( 2 )   2019.2

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    DOI: 10.7567/1882-0786/aafb26

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  240. Vertical GaN p-n diode with deeply etched mesa and the capability of avalanche breakdown

    Fukushima Hayata, Usami Shigeyoshi, Ogura Masaya, Ando Yuto, Tanaka Atsushi, Deki Manato, Kushimoto Maki, Nitta Shugo, Honda Yoshio, Amano Hiroshi

    APPLIED PHYSICS EXPRESS   Vol. 12 ( 2 ) page: 026502   2019.2

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    DOI: 10.7567/1882-0786/aafdb9

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  241. Compositional control of homogeneous InGaN nanowires with the In content up to 90%

    Zeghouane Mohammed, Avit Geoffrey, Andre Yamina, Bougerol Catherine, Robin Yoann, Ferret Pierre, Castelluci Dominique, Gil Evelyne, Dubrovskii Vladimir G., Amano Hiroshi, Trassoudaine Agnes

    NANOTECHNOLOGY   Vol. 30 ( 4 ) page: 044001   2019.1

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    DOI: 10.1088/1361-6528/aaec39

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  242. Localization and transient emission properties in InGaN/ GaN quantum wells of different polarities within core- shell nanorods

    Robin Y., Evropeitsev E. A., Shubina T. V., Kirilenko D. A., Davydov V. Yu., Smirnov A. N., Toropov A. A., Eliseyev I. A., Bae S. Y., Kushimoto M., Nitta S., Ivanov S. V., Amano H.

    NANOSCALE   Vol. 11 ( 1 ) page: 193 - 199   2019.1

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    DOI: 10.1039/c8nr05863f

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  243. Carrier localization structure combined with current micropaths in AlGaN quantum wells grown on an AIN template with macrosteps

    Kojima K., Nagasawa Y., Hirano A., Ippommatsu M., Honda Y., Amano H., Akasaki I., Chichibu S. F.

    APPLIED PHYSICS LETTERS   Vol. 114 ( 1 ) page: 011102   2019.1

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    DOI: 10.1063/1.5063735

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  244. 286 nm monolithic multicomponent system

    Yuan Jialei, Jiang Yan, Shi Zheng, Gao Xumin, Wang Yongjin, Sun Xiaojuan, Li Dabing, Liu Yuhuai, Amano Hiroshi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 58 ( 1 ) page: 010909   2019.1

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    DOI: 10.7567/1347-4065/aaf3aa

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  245. Electronic structure analysis of core structures of threading dislocations in GaN

    Nakano Takashi, Chokawa Kenta, Araidai Masaaki, Shiraishi Kenji, Oshiyama Atsushi, Kusaba Akira, Kangawa Yoshihiro, Tanaka Atsushi, Honda Yoshio, Amano Hiroshi

    2019 COMPOUND SEMICONDUCTOR WEEK (CSW)     page: .   2019

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    DOI: 10.1109/iciprm.2019.8819270

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  246. Light-Emitting Diodes Materials, Processes, Devices and Applications Foreword

    Amano, H

    LIGHT-EMITTING DIODES: MATERIALS, PROCESSES, DEVICES AND APPLICATIONS   Vol. 4   page: V - V   2019

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  247. MOVPE growth and high-temperature annealing of (10(1)over-bar0) AlN layers on (10(1)over-bar0) sapphire

    Dinh Duc V., Amano Hiroshi, Pristovsek Markus

    JOURNAL OF CRYSTAL GROWTH   Vol. 502   page: 14-18   2018.11

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    DOI: 10.1016/j.jcrysgro.2018.09.001

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  248. What is red? On the chromaticity of orange-red InGaN/GaN based LEDs

    Robin Y., Pristovsek M., Amano H., Oehler F., Oliver R. A., Humphreys C. J.

    JOURNAL OF APPLIED PHYSICS   Vol. 124 ( 18 ) page: 183102   2018.11

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  249. Simultaneous Growth of Various InGaN/GaN Core-Shell Microstructures for Color Tunable Device Applications

    Robin Yoann, Liao Yaqiang, Pristovsek Markus, Amano Hiroshi

    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE   Vol. 215 ( 21 ) page: 1800361   2018.11

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    DOI: 10.1002/pssa.201800361

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  250. Analysis of negative electron affinity InGaN photocathode by temperature-programed desorption method

    Kashima Masahiro, Sato Daiki, Koizumi Atsushi, Nishitani Tomohiro, Honda Yoshio, Amano Hiroshi, Iijima Hokuto, Meguro Takashi

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B   Vol. 36 ( 6 ) page: 06JK02   2018.11

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    DOI: 10.1116/1.5048061

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  251. Full-duplex light communication with a monolithic multicomponent system

    Wang Yongjin, Wang Xin, Zhu Bingcheng, Shi Zheng, Yuan Jialei, Gao Xumin, Liu Yuhuai, Sun Xiaojuan, Li Dabing, Amano Hiroshi

    LIGHT-SCIENCE & APPLICATIONS   Vol. 7   page: 83   2018.10

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    DOI: 10.1038/s41377-018-0083-0

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  252. Crystal engineering by tuning the growth kinetics of GaN 3-D microstructures in SAG-HVPE

    Avit Geoffrey, Zeghouane Mohammed, Andre Yamina, Castelluci Dominique, Gil Evelyne, Bae Si-Young, Amano Hiroshi, Trassoudaine Agnes

    CRYSTENGCOMM   Vol. 20 ( 40 ) page: 6207 - 6213   2018.10

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  253. Comparing high-purity c- and m-plane GaN layers for Schottky barrier diodes grown homoepitaxially by metalorganic vapor phase epitaxy

    Nagamatsu Kentaro, Ando Yuto, Ye Zheng, Barry Ousmane, Tanaka Atsushi, Deki Manato, Nitta Shugo, Honda Yoshio, Pristovsek Markus, Amano Hiroshi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 57 ( 10 ) page: 105501   2018.10

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  254. High-temperature thermal annealing of nonpolar (10(1)over-bar0) AlN layers sputtered on (1 0(1)over-bar0) sapphire

    Dinh Duc V, Hu Nan, Honda Yoshio, Amano Hiroshi, Pristovsek Markus

    JOURNAL OF CRYSTAL GROWTH   Vol. 498   page: 377-380   2018.9

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    DOI: 10.1016/j.jcrysgro.2018.07.015

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  255. Advantages of GaN and Related Materials over Si and Issues to be Solved

    AMANO Hiroshi

    Vacuum and Surface Science   Vol. 61 ( 9 ) page: 565 - 567   2018.9

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    DOI: 10.1380/vss.61.565

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  256. Detailed study of effects of duration of pre-AIN-growth trimethylaluminum step on morphologies of GaN layers grown on silicon substrate by metal organic chemical vapor deposition

    Matsumoto Koji, Ono Toshiaki, Honda Yoshio, Murakami Satoshi, Kushimoto Maki, Amano Hiroshi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 57 ( 9 ) page: 091001   2018.9

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  257. Reduction of Residual Impurities in Homoepitaxial m-Plane (10(1)over-bar0) GaN by Using N-2 Carrier Gas in Metalorganic Vapor Phase Epitaxy

    Barry Ousmane I, Lekhal Kaddour, Bae Si-Young, Lee Ho-Jun, Pristovsek Markus, Honda Yoshio, Amano Hiroshi

    PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS   Vol. 12 ( 8 ) page: 1800124   2018.8

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  258. Improvement of breakdown voltage of vertical GaN p-n junction diode with Ga2O3 passivated by sputtering

    Ueoka Yoshihiro, Deki Meneto, Honda Yoshio, Amano Hiroshi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 57 ( 7 ) page: 070302   2018.7

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  259. Study on the Main-Chain Structure of Amorphous Fluorine Resins for Encapsulating AlGaN-Based DUV-LEDs

    Kiho Yamada, Yosuke Nagasawa, Shoko Nagai, Akira Hirano, Masamichi Ippommatsu, Ko Aosaki, Yoshio Honda, Hiroshi Amano, Isamu Akasaki

    Physica Status Solidi (A) Applications and Materials Science   Vol. 215 ( 10 ) page: 1700525   2018.5

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    The main chain structure of optically isotropic amorphous fluorine resin for encapsulating AlGaN-based deep-ultraviolet LEDs (λ &lt
    300 nm) is studied. One type of amorphous fluorine resin has a five-membered ring with a single oxygen atom and the other has that one with two oxygen atoms. Reliability testing is performed using AlGaN-based LEDs of 262 and 289 nm. For the resin with two oxygen atoms in the ring, visible damage to the electrode and significantly increased leakage current are considered to been caused by the photolysis of the ring induced by irradiation with deep-ultraviolet light. In contrast, electrode damage and increased leakage are not observed in the case of the resin with the single-oxygen ring.

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  260. Insight into the performance of multi-color InGaN/GaN nanorod light emitting diodes

    Robin Y., Bae S. Y., Shubina T. V., Pristovsek M., Evropeitsev E. A., Kirilenko D. A., Davydov V. Yu., Smirnov A. N., Toropov A. A., Jmerik V. N., Kushimoto M., Nitta S., Ivanov S. V., Amano H.

    SCIENTIFIC REPORTS   Vol. 8   page: 7311   2018.5

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    DOI: 10.1038/s41598-018-25473-x

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  261. m-Plane GaN Schottky Barrier Diodes Fabricated With MOVPE Layer on Several Off-Angle m-Plane GaN Substrates

    Atsushi Tanaka, Yuto Ando, Kentaro Nagamatsu, Manato Deki, Heajeong Cheong, Barry Ousmane, Maki Kushimoto, Shugo Nitta, Yoshio Honda, Hiroshi Amano

    Physica Status Solidi (A) Applications and Materials Science   Vol. 215 ( 9 ) page: 1700645   2018.5

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    In this study, GaN m-plane Schottky barrier diodes are fabricated by metalorganic vapor-phase epitaxy (MOVPE) on several off-angle gallium nitride (GaN) substrates, and the off-cut angle dependence of impurity incorporation is investigated. We show that the MOVPE layer on the substrate inclined 5° toward the [000–1] direction has extremely low impurity incorporation. These results provide important suggestions for the fabrication of m-plane power devices.

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  262. Interface amorphization in hexagonal boron nitride films on sapphire substrate grown by metalorganic vapor phase epitaxy

    Xu Yang, Shugo Nitta, Markus Pristovsek, Yuhuai Liu, Kentaro Nagamatsu, Maki Kushimoto, Yoshio Honda, Hiroshi Amano

    Applied Physics Express   Vol. 11 ( 5 ) page: 051002   2018.5

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    Hexagonal boron nitride (h-BN) films directly grown on c-plane sapphire substrates by pulsed-mode metalorganic vapor phase epitaxy exhibit an interlayer for growth temperatures above 1200 °C. Cross-sectional transmission electron microscopy shows that this interlayer is amorphous, while the crystalline h-BN layer above has a distinct orientational relationship with the sapphire substrate. Electron energy loss spectroscopy shows the energy-loss peaks of B and N in both the amorphous interlayer and the overlying crystalline h-BN layer, while Al and O signals are also seen in the amorphous interlayer. Thus, the interlayer forms during h-BN growth through the decomposition of the sapphire at elevated temperatures.

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  263. Transferrable monolithic multicomponent system for near-ultraviolet optoelectronics

    Chuan Qin, Xumin Gao, Jialei Yuan, Zheng Shi, Yuan Jiang, Yuhuai Liu, Yongjin Wang, Hiroshi Amano

    Applied Physics Express   Vol. 11 ( 5 ) page: 051201   2018.5

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    A monolithic near-ultraviolet multicomponent system is implemented on a 0.8-mm-diameter suspended membrane by integrating a transmitter, waveguide, and receiver into a single chip. Two identical InGaN/Al0.10Ga0.90N multiple-quantum well (MQW) diodes are fabricated using the same process flow, which separately function as a transmitter and receiver. There is a spectral overlap between the emission and detection spectra of the MQW diodes. Therefore, the receiver can respond to changes in the emission of the transmitter. The multicomponent system is mechanically transferred from silicon, and the wire-bonded transmitter on glass experimentally demonstrates spatial light transmission at 200 Mbps using non-return-to-zero on–off keying modulation.

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  264. Correlation between dislocations and leakage current of p-n diodes on a free-standing GaN substrate

    Shigeyoshi Usami, Yuto Ando, Atsushi Tanaka, Kentaro Nagamatsu, Manato Deki, Maki Kushimoto, Shugo Nitta, Yoshio Honda, Hiroshi Amano, Yoshihiro Sugawara, Yong-Zhao Yao, Yukari Ishikawa

    APPLIED PHYSICS LETTERS   Vol. 112 ( 18 ) page: 182106   2018.4

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    Dislocations that cause a reverse leakage current in vertical p-n diodes on a GaN free-standing substrate were investigated. Under a high reverse bias, dot-like leakage spots were observed using an emission microscope. Subsequent cathodoluminescence (CL) observations revealed that the leakage spots coincided with part of the CL dark spots, indicating that some types of dislocation cause reverse leakage. When etch pits were formed on the dislocations by KOH etching, three sizes of etch pits were obtained (large, medium, and small). Among these etch pits, only the medium pits coincided with leakage spots. Additionally, transmission electron microscopy observations revealed that pure screw dislocations are present under the leakage spots. The results revealed that lc pure screw dislocations are related to the reverse leakage in vertical p-n diodes. Published by AIP Publishing.

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  265. Light output performance of red AlGaInP-based light emitting diodes with different chip geometries and structures

    Oh Jeong-Tak, Lee Sang-Youl, Moon Yong-Tae, Moon Ji Hyung, Park Sunwoo, Hong Ki Yong, Song Ki Young, Oh Chan-Hyoung, Shim Jong-In, Jeong Hwan-Hee, Song June-O, Amano Hiroshi, Seong Tae-Yeon

    OPTICS EXPRESS   Vol. 26 ( 9 ) page: 11194-11200   2018.4

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    DOI: 10.1364/OE.26.011194

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  266. The 2018 GaN power electronics roadmap

    H. Amano, Y. Baines, E. Beam, Matteo Borga, T. Bouchet, Paul R Chalker, M. Charles, Kevin J Chen, Nadim Chowdhury, Rongming Chu, Carlo De Santi, Maria Merlyne De Souza, Stefaan Decoutere, L. Di Cioccio, Bernd Eckardt, Takashi Egawa, P. Fay, Joseph J Freedsman, L. Guido, Oliver Häberlen, Geoff Haynes, Thomas Heckel, Dilini Hemakumara, Peter Houston, Jie Hu, Mengyuan Hua, Qingyun Huang, Alex Huang, Sheng Jiang, H. Kawai, Dan Kinzer, Martin Kuball, Ashwani Kumar, Kean Boon Lee, Xu Li, Denis Marcon, Martin März, R. McCarthy, Gaudenzio Meneghesso, Matteo Meneghini, E. Morvan, A. Nakajima, E. M.S. Narayanan, Stephen Oliver, Tomás Palacios, Daniel Piedra, M. Plissonnier, R. Reddy, Min Sun, Iain Thayne, A. Torres, Nicola Trivellin, V. Unni, Michael J Uren, Marleen Van Hove, David J Wallis, J. Wang, J. Xie, S. Yagi, Shu Yang, C. Youtsey, Ruiyang Yu, Enrico Zanoni, Stefan Zeltner, Yuhao Zhang

    Journal of Physics D: Applied Physics   Vol. 51 ( 16 ) page: 163001   2018.4

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    Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

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  267. Analysis of Cesium Layer on InGaN by Temperature Programmed Desorption Method

    Kashima Masahiro, Daiki Sato, Atsushi Koizumi, Tomohiro Nishitani, Yoshio Honda, Hiroshi Amano, Hokuto Iijima, Takashi Meguro

    JSAP Annual Meetings Extended Abstracts   Vol. 2018.1 ( 0 ) page: 1670 - 1670   2018.3

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    DOI: 10.11470/jsapmeeting.2018.1.0_1670

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  268. Growth of hexagonal boron nitride on sapphire substrate by pulsed-mode metalorganic vapor phase epitaxy

    Xu Yang, Shugo Nitta, Kentaro Nagamatsu, Si-Young Bae, Ho-Jun Lee, Yuhuai Liu, Markus Pristovsek, Yoshio Honda, Hiroshi Amano

    JOURNAL OF CRYSTAL GROWTH   Vol. 482 ( 15 ) page: 1 - 8   2018.1

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    Hexagonal boron nitride (h-BN) was directly grown on sapphire substrate using alternating ammonia (NH3) and triethylboron (TEB) supply (pulsed mode) in metalorganic vapor phase epitaxy. The best condition is when just enough NH3 is supplied to fully convert the TEB within one cycle. Excess NH3 caused islands on h-BN film surface while a lack of NH3 does not form h-BN at all. The epitaxial relationship between grown h-BN layer and c-plane sapphire was confirmed to be [0001](h-BN)||[0001](sapphire) and [10-10](h-BN)||[11-20](sapphire). It is known that, compared to AlN, BN requires higher V/III ratios for good crystallinity, which due to severe gas-phase reactions is difficult to achieve using continuous supply. Thus using pulsed mode the FWHM of the symmetric (0002) diffraction was almost halved and the growth rate was several times faster. (C) 2017 Elsevier B.V. All rights reserved.

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  269. Electrical and Thermal Analysis of Vertical GaN-on-GaN PN Diodes

    Yates Luke, Pavlidis Georges, Graham Samuel, Usami Shigeyoshi, Nagamatsu Kentaro, Honda Yoshio, Amano Hiroshi

    PROCEEDINGS OF THE 17TH IEEE INTERSOCIETY CONFERENCE ON THERMAL AND THERMOMECHANICAL PHENOMENA IN ELECTRONIC SYSTEMS (ITHERM 2018)     page: 831 - 837   2018

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  270. Theoretical Study of the Electronic Structure of Threading Edge Dislocations in GaN

    Nakano Takashi, Araidai Masaaki, Shiraishi Kenji, Tanaka Atsushi, Honda Yoshio, Amano Hiroshi

    GALLIUM NITRIDE AND SILICON CARBIDE POWER TECHNOLOGIES 8   Vol. 86 ( 12 ) page: 41 - 49   2018

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    DOI: 10.1149/08612.0041ecst

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  271. DFT modeling of carbon incorporation in GaN(0001) and GaN(000(1)over-bar) metalorganic vapor phase epitaxy Reviewed

    Pawel Kempisty, Yoshihiro Kangawa, Akira Kusaba, Kenji Shiraishi, Stanislaw Krukowski, Michal Bockowski, Koichi Kakimoto, and Hiroshi Amano

    APPLIED PHYSICS LETTERS   Vol. 111   page: 141602/1-5   2017.10

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    The carbon incorporation mechanism in GaN(0001) and GaN(000 (1) over bar) during MOVPE was investigated using density functional theory (DFT) calculations. The results confirm that the crucial factors for carbon incorporation are Fermi level pinning and accompanying surface band bending. In addition, the lattice symmetry has a strong dependence on the stability of carbon in a few subsurface layers, which results from interactions between the impurities and surface states. It was shown that these effects are responsible for facilitating or hindering the incorporation of impurities and dopants. The influence of diluent gas species (hydrogen or nitrogen) on carbon incorporation was discussed.

    DOI: 10.1063/1.4991608

  272. Initial leakage current paths in the vertical-type GaN-on-GaN Schottky barrier diodes

    Liwen Sang, Bing Ren, Masatomo Sumiya, Meiyong Liao, Yasuo Koide, Atsushi Tanaka, Yujin Cho, Yoshitomo Harada, Toshihide Nabatame, Takashi Sekiguchi, Shigeyoshi Usami, Yoshio Honda, and Hiroshi Amano

    APPLIED PHYSICS LETTERS   Vol. 111   page: 122102/1-5   2017.9

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    Electrical characteristics of leakage current paths in vertical-type n-GaN Schottky barrier diodes (SBDs) on free-standing GaN substrates are investigated by using photon emission microscopy (PEM). The PEM mapping shows that the initial failure of the SBD devices at low voltages is due to the leakage current paths from polygonal pits in the GaN epilayers. It is observed that these polygonal pits originate from carbon impurity accumulation to the dislocations with a screw-type component by microstructure analysis. For the SBD without polygonal pits, no initial failure is observed and the first leakage appeals at the edge of electrodes as a result of electric field concentration. The mechanism of leakage at pits is explained in terms of trap assisted tunneling through fitting current-voltage characteristics.

    DOI: 10.1063/1.4994627

  273. Absolute technique for measuring internal electric fields in InGaN/GaN light-emitting diodes by electroreflectance applicable to all crystal orientations Reviewed

    Tomoyuki Tanikawa, Kanako Shojiki, Ryuji Katayama, Shigeyuki Kuboya, Takashi Matsuoka, Yoshio Honda, and Hiroshi Amano

    Applied Physics Express   Vol. 10   page: 082101/1-4   2017.8

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    DOI: 10.7567/APEX.10.082101

  274. Low cost high voltage GaN polarization superjunction field effect transistors

    H. Kawai, S. Yagi, S. Hirata, F. Nakamura, T. Saito, Y. Kamiyama, M. Yamamoto, H. Amano, V. Unni, E. M. S. Narayanan

    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE   Vol. 214 ( 8 ) page: 1600834/1-10   2017.8

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    A comprehensive overview of the novel high voltage GaN field effect transistors (FETs) based on the Polarization Superjunction (PSJ) concept, and a cost-effective approach towards manufacturing these high performance devices are presented. Current challenges impeding wider adoption of GaN power switching transistors in applications, and the latest results of the scaled-up PSJ-FETs from POWDEC KK, are also discussed. The article also presents hard-switching characteristics of 400-800V boost converter, constructed using a PSJ-FET grown on sapphire substrate, and the future direction of GaN power semiconductor technology based on monolithic integration for advanced power electronics.

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  275. Facet dependence of leakage current and carrier concentration in m-plane GaN Schottky barrier diode fabricated with MOVPE Reviewed

    Atsushi Tanaka, Ousmane1 Barry, Kentaro Nagamatsu, Junya Matsushita, Manato Deki, Yuto Ando, Maki Kushimoto, Shugo Nitta, Yoshio Honda, and Hiroshi Amano

    Phys. Status Solidi A   Vol. 214 ( 8 ) page: 1600829/1-5   2017.8

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    In this study, GaN m-plane Schottky barrier diodes fabricated with a metalorganic vapor-phase epitaxy on a GaN substrate were investigated using emission microscope, photoluminescence, and cathodoluminescence. In addition, facet dependence of leakage current under reverse-biased condition was observed. We showed that the leakage-current distribution was caused by the facet dependence of the carrier concentration and oxygen concentration. These results can provide important suggestions for the fabrication of m-plane devices. (a) four-faceted hillocks on m-plane GaN MOVPE sample, facet dependence of (b) leakage current and (c) PL peak intensity of the m-plane GaN Schottky barrier diode.

    DOI: 10.1002/pssa.201600829

  276. Effect of dislocations on the growth of p-type GaN and on the characteristics of p-n diodes Invited Reviewed

    Shigeyoshi Usami, Ryosuke Miyagoshi, Atsushi Tanaka, Kentaro Nagamatsu, Maki Kushimoto, Manato Deki, Shugo Nitta, Yoshio Honda, and Hiroshi Amano

    Phys. Status Solidi A   Vol. 214 ( 8 ) page: 1600837/1-5   2017.8

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    We investigate the influence of crystal defects on p-type GaN grown by metalorganic vapor phase epitaxy. Sets of p-type GaN films were grown on sapphire substrates and on free-standing GaN (F-GaN) substrates simultaneously using various Et-Cp2Mg flow rates. Although there is a difference of two orders of magnitude between the threading dislocation densities of p-type GaN grown on sapphire and F-GaN substrates, there is no significant difference in hole concentration. However, there are problems with the surface morphology of p-type GaN grown on sapphire. The deterioration of the surface was caused by the difference in nanopipe density. The electrical properties of a p-n junction diode formed on sapphire with a high density of nanopipes were observed using emission microscopy under both forward- and reverse-bias conditions. Our results demonstrate that the nanopipes are electrically inactive, and that other types of threading dislocation have more influence on the current-voltage characteristics.

    DOI: 10.1002/pssb.201600722

  277. Selective-area growth of doped GaN nanorods by pulsed-mode MOCVD: Effect of Si and Mg dopants Reviewed

    Si-Young Bae, Kaddour Lekhal, Ho-Jun Lee, Jung-Wook Min, Dong-Seon Lee, Yoshio Honda, and Hiroshi Amano

    Phys. Status Solidi B   Vol. 254 ( 8 ) page: 1600722/1-7   2017.8

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    Injecting current with a uniform carrier concentration is important for applications with three-dimensional architectures such as vertical power devices or displays. In III-nitride nanostructures, dopants not only incorporate differently depending on the surface orientation but can also seriously affect the kinetic equilibrium shapes of the nanorods. Herein, we report selective-area growth of doped GaN nanorods grown by pulsed-mode metalorganic chemical vapor deposition. Two dopants, Si and Mg, were employed as donor and acceptor atoms, respectively, for a mono-doping approach. Furthermore, a mixed flow of Si and Mg was supplied for a co-doping approach. We compared the morphological effects and growth rates of each doped GaN nanorod array. Then, we proposed appropriate growth mechanisms for the doped GaN nanorods on the basis of our structural characterizations. These results might extend the morphological functionality of GaN nanorods by including doping and may also provide an appropriate foundation for the design of nanostructure-based electronic or photonic devices.

    DOI: 10.1002/pssb.201600722

  278. Decomposition of trimethylgallium and adduct formation in a metalorganic vapor phase epitaxy reactor analyzed by high-resolution gas monitoring system Reviewed

    Kentaro Nagamatsu, Shugo Nitta, Zheng Ye, Hirofumi Nagao, Shinichi Miki, Yoshio Honda, and Hiroshi Amano

    Phys. Status Solidi B   Vol. 254 ( 8 ) page: 1600737/1-4   2017.8

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    DOI: 10.1002/pssb.201600737

  279. Effect of dislocations on the growth of p-type GaN and on the characteristics of p-n diodes

    Usami Shigeyoshi, Miyagoshi Ryosuke, Tanaka Atsushi, Nagamatsu Kentaro, Kushimoto Maki, Deki Manato, Nitta Shugo, Honda Yoshio, Amano Hiroshi

    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE   Vol. 214 ( 8 )   2017.8

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    We investigate the influence of crystal defects on p-type GaN grown by metalorganic vapor phase epitaxy. Sets of p-type GaN films were grown on sapphire substrates and on free-standing GaN (F-GaN) substrates simultaneously using various Et-Cp2Mg flow rates. Although there is a difference of two orders of magnitude between the threading dislocation densities of p-type GaN grown on sapphire and F-GaN substrates, there is no significant difference in hole concentration. However, there are problems with the surface morphology of p-type GaN grown on sapphire. The deterioration of the surface was caused by the difference in nanopipe density. The electrical properties of a p–n junction diode formed on sapphire with a high density of nanopipes were observed using emission microscopy under both forward- and reverse-bias conditions. Our results demonstrate that the nanopipes are electrically inactive, and that other types of threading dislocation have more influence on the current–voltage characteristics.

    DOI: 10.1002/pssa.201600837

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  280. Role of threading dislocations in strain relaxation during GaInN growth monitored by real-time X-ray reflectivity Reviewed

    Guangxu Ju, Masao Tabuchi, Yoshikazu Takeda, and Hiroshi Amano

    Applied Physics Letters   Vol. 110 ( 26 ) page: 262105/1-5   2017.6

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    DOI: 10.1063/1.4990687

  281. A-plane GaN growth on (11-20) 4H-SiC substrate with an ultrathin interlayer Reviewed

    Zheng Sun, Peifeng Song, Shugo Nitta, Yoshio Honda, Hiroshi Amano

    Journal of Crystal Growth   Vol. 468   page: 866-869   2017.6

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    DOI: 10.1016/j.jcrysgro.2017.01.31

  282. Selective-area growth of vertically oriented GaN nanostructures with a hafnium pre-orienting layer Reviewed

    S.-Y.Bae, K. Lekhal, H.-J.Lee, T.Mitsunari, J.-W.Min, D.-S.Leed, M.Kushimoto, Y.Honda, H.Amano

    Journal of Crystal Growth   Vol. 468   page: 110-113   2017.6

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    DOI: 10.1016/j.jcrysgro.2016.10.032

  283. Orientation-controlled epitaxial lateral overgrowth of semipolar GaN on Si(001) with a directionally sputtered AlN buffer layer Reviewed

    Ho-Jun Lee, Si-Young Bae, Kaddour Lekhal, Akira Tamura, Takafumi Suzuki, Maki Kushimoto, Yoshio Honda, and Hiroshi Amano

    Journal of Crystal Growth   Vol. 468   page: 547-551   2017.6

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    DOI: 10.1016/j.jcrysgro.2016.11.116

  284. Effect of V/III ratio on the surface morphology and electrical properties of m–plane ( 101¯0 ) GaN homoepitaxial layers Reviewed

      Vol. 468   page: 552-556   2017.6

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    We have investigated the effect of V/III ratio on the surface morphology, impurity concentration and electrical properties of m–plane (101¯0) Gallium Nitride (GaN) homoepitaxial layers. Four-sided pyramidal hillocks are observed on the nominally on-axis m–plane GaN films. Hillocks sizes relatively increase by increasing the V/III ratio. All facets of pyramidal hillocks exhibit well-defined step-terrace features. Secondary ion mass spectrometry depth profiles reveal that carbon impurities decrease by increasing the V/III ratio while the lowest oxygen content is found at an optimized V/III ratio of 900. Vertical Schottky barrier diodes fabricated on the m–GaN samples were characterized. Low leakage current densities of the order of 10−10 A/cm2 at −5 V are obtained at the optimum V/III ratio. Oxygen impurities and screw-component dislocations around hillocks are found to have more detrimental impact on the leakage current mechanism.

    DOI: 10.1016/j.jcrysgro.2016.12.012

  285. Annealing effect on threading dislocations in a GaN grown on Si substrate Reviewed

      Vol. 468   page: 835-838   2017.6

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    Effect of rapid thermal annealing (RTA) on crystal defects in a GaN layer grown on a (111)Si substrate was investigated by photoluminescence (PL) and transmission electron microscopy (TEM) analyses. The PL spectra suggested that the density of gallium vacancy is not changed by the heat treatment up to 700 °C. In the TEM specimen, we had dislocation half loops generated by off-axis propagation of the threading dislocation. We found that the half-loop of c-type dislocation shrinks/moves by a repetitive RTA at 600–700 °C. In contrast, we could find no remarkable changes in the a-type or a+c-type dislocations.

    DOI: 10.1016/j.jcrysgro.2017.01.001

  286. A-plane GaN growth on (11-20) 4H-SiC substrate with an ultrathin interlayer

    Sun Zheng, Song Peifeng, Nitta Shugo, Honda Yoshio, Amano Hiroshi

    JOURNAL OF CRYSTAL GROWTH   Vol. 468   page: 866 - 869   2017.6

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    A-plane GaN was attempted to be grown on (11-20) 4H-SiC bulk substrate without using a traditional thick buffer layer. By inducing TMAl treatment before the GaN growth step and using both a low pressure and V/III ratio, the interlayer thickness of the a-plane GaN/SiC was reduced to 1.7+0.5 nm. The ultrathin interlayer was observed to be either AlN or AlGaN with a low Ga composition. This study is aimed to contribute to the understanding of GaN growth on the sidewalls of c-plane trench structure SiC. The ultrathin growth technique is also hoped to be applied to the fabrication of GaN-based vertical structure nonpolar optical or electrical devices.

    DOI: 10.1016/j.jcrysgro.2017.01.031

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  287. Uneven AlGaN multiple quantum well for deep-ultraviolet LEDs grown on macrosteps and impact on electroluminescence spectral output Reviewed

    Michiko Kaneda, Cyril Pernot, Yosuke Nagasawa, Akira Hirano, Masamichi Ippommatsu, Yoshio Honda, Hiroshi Amano, and Isamu Akasaki

    Japanese Journal of Applied Physics   Vol. 56   page: 061002   2017.5

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    DOI: 10.7567/JJAP.56.061002

  288. III-nitride core-shell nanorod array on quartz substrates

    Si-Young Bae, Jung-Wook Min, Hyeong-Yong Hwang, Kaddour Lekhal, Ho-Jun Lee, Young-Dahl Jho, Dong-Seon Lee, Yong-Tak Lee, Nobuyuki Ikarashi, Yoshio Honda, Hiroshi Amano

    SCIENTIFIC REPORTS   Vol. 7   page: 45345   2017.3

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    We report the fabrication of near-vertically elongated GaN nanorods on quartz substrates. To control the preferred orientation and length of individual GaN nanorods, we combined molecular beam epitaxy (MBE) with pulsed-mode metal-organic chemical vapor deposition (MOCVD). The MBE-grown buffer layer was composed of GaN nanograins exhibiting an ordered surface and preferred orientation along the surface normal direction. Position-controlled growth of the GaN nanorods was achieved by selective-area growth using MOCVD. Simultaneously, the GaN nanorods were elongated by the pulsed-mode growth. The microstructural and optical properties of both GaN nanorods and InGaN/GaN core-shell nanorods were then investigated. The nanorods were highly crystalline and the core-shell structures exhibited optical emission properties, indicating the feasibility of fabricating III-nitride nano-optoelectronic devices on amorphous substrates.

    DOI: 10.1038/srep45345

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  289. Investigation of reduction of light absorption at p-side toward UV emitting devices

    Yasuda Toshiki, Kuwabara Natsuko, Takeuchi Tetsuya, Iwaya Motoaki, Kamiyama Satoshi, Akasaki Isamu, Amano Hiroshi

    JSAP Annual Meetings Extended Abstracts   Vol. 2017.1 ( 0 ) page: 3400 - 3400   2017.3

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    DOI: 10.11470/jsapmeeting.2017.1.0_3400

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  290. Effect of thermal treatment on the quantu efficiency of NEA-InGaN photocatode

    Kashima Masahiro, Iijima Hokuto, Nishitani Tomohiro, Sato Daiki, Honda Yoshio, Amano Hiroshi, Meguro Takashi

    JSAP Annual Meetings Extended Abstracts   Vol. 2017.1 ( 0 ) page: 1554 - 1554   2017.3

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    DOI: 10.11470/jsapmeeting.2017.1.0_1554

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  291. A Study on the Photo-resistance and the Decomposition Mechanism of Perfluoro Resins Applied to Encapsulating Deep Ultra Violet LEDs

    Nagasawa Yosuke, Yamada Kiho, Nagai Shouko, Hirano Akira, Ipponmatsu Masamichi, Aosaki Ko, Honda Yoshio, Amano Hiroshi, Akasaki Isamu

    JSAP Annual Meetings Extended Abstracts   Vol. 2017.1 ( 0 ) page: 1136 - 1136   2017.3

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    DOI: 10.11470/jsapmeeting.2017.1.0_1136

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  292. Relationship between lattice relaxation and electrical properties in polarization doping of graded AlGaN with high AlN mole fraction on AlGaN template

    Yasuda Toshiki, Takeuchi Tetsuya, Iwaya Motoaki, Kamiyama Satoshi, Akasaki Isamu, Amano Hiroshi

    APPLIED PHYSICS EXPRESS   Vol. 10 ( 2 )   2017.2

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    We investigated polarization doping for hole generation in abrupt and graded GaN/Al0.7Ga0.3N interfaces on Al0.99Ga0.01N templates. The abrupt interface exhibited hole generation, whereas the graded interface exhibited electron generation. In the graded AlxGa1%xN (x = 0.65-0), a graded part with an AlN mole fraction ranging from 0.2 to 0 showed a large relaxation. Theoretical estimation revealed that this part contained positive polarization charges, accumulating electrons. Via Mg doping in the graded AlGaN layer, we obtained a high hole concentration of 3 ' 1013cm%2. These results indicate that understanding the relaxation conditions in the graded layer is indispensable for polarization doping.

    DOI: 10.7567/APEX.10.025502

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  293. Relationship between lattice relaxation and electrical properties in polarization doping of graded AlGaN with high AlN mole fraction on AlGaN template Reviewed

    Toshiki Yasuda, Tetsuya Takeuchi, Motoaki Iwaya, Satoshi Kamiyama, Isamu Akasaki and Hiroshi Amano

    Applied Physics Express   Vol. 10   page: 025502   2017.1

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    DOI: https://doi.org/10.4567/APEX.10.025502

  294. From the dawn of gan-based light-emitting devices to the present day

    Amano H.

    Handbook of Solid-State Lighting and LEDs     page: 3-12   2017.1

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    DOI: 10.1201/9781315151595

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  295. High quality Al0.99Ga0.01N layers on sapphire substrates grown at 1150 degrees C by metalorganic vapor phase epitaxy

    Katsuno Shota, Yasuda Toshiki, Hagiwara Koudai, Koide Norikatsu, Iwaya Motoaki, Takeuchi Tetsuya, Kamiyama Satoshi, Akasaki Isamu, Amano Hiroshi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 56 ( 1 )   2017.1

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    DOI: 10.7567/JJAP.56.015504

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  296. Reduction of Dislocations in GaN on Silicon Substrate Using In Situ Etching Reviewed

    Koji Matsumoto, Toshiaki Ono, Yoshio Honda, Tetsuya Yamamoto, Shigeyoshi Usami, Maki Kushimoto, Satoshi Murakami, and Hiroshi Amano

    Physica Status Solidi b   Vol. 253   page: 1700387(1-7)   2017

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    A gallium nitride (GaN) epitaxial layer with a low density of threading dislocations is successfully grown on a silicon substrate by using in situ gas
    etching. Silicon nitride (SiNx) film is used as a mask, and ammonia is intermittently supplied in hydrogen ambient during the etching. After etching,
    high-density deep pits appeared on the surface of a GaN template layer and corresponded to the threading dislocations in the layer. In this novel method,
    before growing an additional GaN layer on the template GaN layer, a second SiNx layer is deposited after the etching process, and this layer prevents GaN nuclei from growing on the upper side-walls of the pits. By using this method, the density of threading dislocations of the GaN surface is reduced to 6.7E7 cm2. This method is cost effective, completing all the necessary processes in one growth run without taking samples out from a metalorganic chemical vapor deposition (MOCVD) reactor.

    DOI: 10.1002/pssb.201700387

  297. Development of Sustainable Smart Society based on Transformative Electronics

    Ogura M., Ando Y., Usami S., Nagamatsu K., Kushimoto M., Deki M., Tanaka A., Nitta S., Honda Y., Pristovsek M., Kawai H., Yagi S., Amano H.

    2017 IEEE INTERNATIONAL ELECTRON DEVICES MEETING (IEDM)     page: .   2017

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  298. Progress and prospect of growth of wide-band-gap group III nitrides

    Hiroshi Amano

    Topics in Applied Physics   Vol. 133   page: 1 - 9   2017

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    GaAs, InP, and their related compound semiconductors can be grown on native substrates, whereas such growth was not possible for group III nitride semiconductors in the 1970s and 1980s. Despite this drawback, researchers were able to use novel functions of group III nitride semiconductors by growing their thin films on nonnative substrates such as sapphire SiC and Si.

    DOI: 10.1007/978-981-10-3755-9_1

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  299. From the Dawn of GaN-Based Light-Emitting Devices to the Present Day

    Amano Hiroshi

    HANDBOOK OF SOLID-STATE LIGHTING AND LEDS     page: 3 - 11   2017

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  300. High quality Al0.99Ga0.01N layers on sapphire substrates grown at 1150 °C by metalorganic vapor phase epitaxy Reviewed

    Shota Katsuno, Toshiki Yasuda, Koudai Hagiwara, Norikatsu Koide, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki, and Hiroshi Amano

    Japanese Journal of Applied Physics   Vol. 56   page: 015504   2016.12

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    DOI: https://doi.org/10.7567/JJAP.56.015504

  301. Improved crystal quality of semipolar (10(1)over-bar3) GaN on Si(001) substrates using AlN/GaN superlattice interlayer Reviewed

    Ho-Jun Lee, Si-Young Bae, Kaddour Lekhal, Tadashi Mitsunaria, Akira Tamura, Yoshio Honda, Hiroshi Amano

    Journal of Crystal Growth   Vol. 454   page: 114-120   2016.11

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    DOI: https://doi.org/10.1016/j.jcrysgro.2016.09.004

  302. Controlled morphology of regular GaN microrod arrays by selective area growth with HVPE Reviewed

    Kaddour Lekhal, Si-Young Bae, Ho-Jun Lee, Tadashi Mitsunari, Akira Tamura, Manato Deki, Yoshio Honda, Hiroshi Amano

    Journal of Crystal Growth   Vol. 447   page: 55-61   2016.8

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    The selective area growth (SAG) of GaN was implemented on patterned GaN/sapphire templates by hydride vapor phase epitaxy (HVPE) to fabricate regular arrays of Ga-polar GaN microrods. The control of growth parameters such as H2/N2 carrier gas ratio, growth temperature, and absolute NH3/HCl gas flow resulted in changes in the growth morphology.

    DOI: 10.1016/j.jcrysgro.2016.05.008

  303. Development of highly durable deep-ultraviolet AlGaN-based LED multichip array with hemispherical encapsulated structures using a selected resin through a detailed feasibility study Reviewed

    Shoko Nagai, Kiho Yamada, Akira Hirano, Masamichi Ippommatsu, Masahiro Ito, Naoki Morishima, Ko Aosaki, Yoshio Honda, Hiroshi Amano, and Isamu Akasaki

    Japanese Journal of Applied Physics   Vol. 55   page: 082101/1-7   2016.8

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    DOI: http://doi.org/10.7567/JJAP.55.082101

  304. Deep level study of Mg-doped GaN using deep level transient spectroscopy and minority carrier transient spectroscopy Reviewed

    Tran Thien Duc, Galia Pozina, Hiroshi Amano, Bo Monemar, Erik Janz´en, and Carl Hemmingsson

    PHYSICAL REVIEW   Vol. B94   page: 045206/1-8   2016.7

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    Deep levels in Mg-doped GaN grown by metal organic chemical vapor deposition, undoped GaN grown by MOCVD, and halide vapor phase epitaxy-grown GaN have been studied using deep level transient spectroscopy and minority charge carrier transient spectroscopy.

    DOI: 10.1103/PhysRevB.94.045206

  305. Study of radiation detection properties of GaN pn diode Reviewed

    Mutsuhito Sugiura, Maki Kushimoto, Tadashi Mitsunari, Kohei Yamashita, Yoshio Honda, Hiroshi Amano, Yoku Inoue, Hidenori Mimura, Toru Aoki, and Takayuki Nakano

    Japanese Journal of Applied Physics   Vol. 55   page: 05FJ02/1-3   2016.5

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    Recently, GaN, which has remarkable properties as a material for optical devices and high power electron devices, has also attracted attention as a material for radiation detectors. We previously suggested the use of BGaN as a neutron detector material. However, the radiation detection characteristics of GaN itself are not yet adequately understood. For realizing a BGaN neutron detector, the understanding of the radiation detection characteristics of GaN, which is a base material of the neutron detector, is important. In this study, we evaluated the radiation detection characteristics of GaN. We performed I V and energy spectrum measurements under alpha ray, gamma ray, and thermal neutron irradiations to characterize the radiation detection characteristics of a GaN diode. The obtained results indicate that GaN is an effective material for our proposed new BGaN-based neutron detector.

  306. Low-ohmic-contact-resistance V-based electrode for n-type AlGaN with high AlN molar fraction Reviewed

    Kazuki Mori, Kunihiro Takeda, Toshiki Kusafuka, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki and Hiroshi Amano

    Low-ohmic-contact-resistance V-based electrode for n-type AlGaN with high AlN molar fraction   Vol. 55 ( 5S ) page: 05FL03/1-5   2016.5

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  307. Observation of relaxation time of surface charge limit for InGaN photocathodes with negative electron affinity Reviewed

    Daiki Sato, Tomohiro Nishitani, Yoshio Honda and Hiroshi Amano

    Japanese Journal of Applied Physics   Vol. 55 ( 5S ) page: 05FH05/1-4   2016.5

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  308. Emission Characteristics of InGaN/GaN Core-Shell Nanorods Embedded in a 3D Light-Emitting Diode Reviewed

    Byung Oh Jung, Si-Young Bae, Seunga Lee, Sang Yun Kim, Jeong Yong Lee, Yoshio Honda and Hiroshi Amano

    Nanoscale Research Letters   Vol. 11   2016.4

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    We report the selective-area growth of a gallium nitride (GaN)-nanorod-based InGaN/GaN multiple-quantum-well (MQW) core-shell structure embedded in a three-dimensional (3D) light-emitting diode (LED) grown by metalorganic chemical vapor deposition (MOCVD) and its optical analysis. High-resolution transmission electron microscopy (HR-TEM) observation revealed the high quality of the GaN nanorods and the position dependence of the structural properties of the InGaN/GaN MQWs on multiple facets. The excitation and temperature dependences of photoluminescence (PL) revealed the m-plane emission behaviors of the InGaN/GaN core-shell nanorods. The electroluminescence (EL) of the InGaN/GaN core-shell-nanorod-embedded 3D LED changed color from green to blue with increasing injection current. This phenomenon was mainly due to the energy gradient and deep localization of the indium in the selectively grown InGaN/GaN core-shell MQWs on the 3D architecture.

    DOI: 10.1186/s11671-016-1441-6

  309. Preflow trimethylaluminum treatment effect on GaN growth on SiC with an ultrathin interlayer Reviewed

    Zheng Sun, Kentaro Nagamatsu, Marc Olsson, Peifeng Song, Manato Deki, Shugo Nitta, Yoshio Honda and Hiroshi Amano

    Japanese Journal of Applied Physics,   Vol. 55 ( 5S ) page: 05FB06/1-5   2016.4

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  310. Growth of semipolar (1-101) high-indium-content InGaN quantum well using InGaN tilting layer on Si(001) Reviewed

    Maki Kushimoto, Yoshio Honda and Hiroshi Amano

    Japanese Journal of Applied Physics   Vol. 55 ( 5S ) page: 05FA10/1-4   2016.4

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  311. Evaluation of excess In during metal organic vapor-phase epitaxy growth of InGaN by monitoring via in situ laser scattering Reviewed

    Tetsuya Yamamoto, Akira Tamura, Shigeyoshi Usami, Tadashi Mitsunari, Kentaro Nagamatsu, Shugo Nitta, Yoshio Honda and Hiroshi Amano

    Japanese Journal of Applied Physics   Vol. 55 ( 5S ) page: 05FD03/1-4   2016.4

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    Using an in situ laser absorption and scattering method, the surface roughness and incorporation of In in InGaN layers grown by metal organic vapor-phase epitaxy (MOVPE) were monitored.

  312. Development of GaN-based blue LEDs and metalorganic vapor phase epitaxy of GaN and related materials

    Hiroshi Amano

    Progress in Crystal Growth and Characterization of Materials   Vol. 62   page: 126–135   2016.4

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    DOI: https://doi.org/10.1016/j.pcrysgrow.2016.04.006

  313. Structural and optical study of core–shell InGaN layers of nanorod arrays with multiple stacks of InGaN/GaN superlattices for absorption of longer solar spectrum Reviewed

      Vol. 55 ( 5S ) page: 05FG03/1-8   2016.4

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    We report on the material and optical properties of core–shell InGaN layers grown on GaN nanorod arrays. The core–shell InGaN layers were well grown on polarization-reduced surfaces such as semipolar pyramids and nonpolar sidewalls. In addition, to compensate the biaxial strain between GaN and InGaN layers, we grew interlayers underneath a thick InGaN layer. Here, the interlayers were composed of multiple superlattice structures. We could observe that the indium composition of core–shell InGaN structures increased with the number of interlayers. This indicates that the absorption energy band of InGaN alloys can be better matched to the spectral irradiance of the solar spectrum in nature. We also implemented a simulation of Ga-polar and nonpolar InGaN-based solar cells based on the indium composition obtained from the experiments. The result showed that nonpolar InGaN solar cells had a much higher efficiency than Ga-polar InGaN solar cells with the same thickness of the absorption layer.

  314. Selective-area growth of GaN microrods on strain-induced templates by hydride vapor phase epitaxy Reviewed

    Kaddour Lekhal, Si-Young Bae, Ho-Jun Lee, Tadashi Mitsunari, Akira Tamura, Manato Deki, Yoshio Honda and Hiroshi Amano

    Japanese Journal of Applied Physics   Vol. 55   page: 05FF03/1-5   2016.3

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  315. Theoretical approach to surface reconstruction of InN(0001) during raised-pressure metalorganic vapor-phase epitaxy Reviewed

    Akira Kusaba, Yoshihiro Kangawa, Yoshio Honda, Hiroshi Amano and Koichi Kakimoto

    Japanese Journal of Applied Physics   Vol. 55 ( 5S ) page: 05FM01/1-4   2016.2

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  316. Study of enhanced photovoltaic behavior in InGaN-based solar cells by using SiNx insertion layer: Influence of dislocations Reviewed

    Seunga Lee, Yoshio Honda, Hiroshi Amano, Jongjin Jang and Okhyun Nam

    Japanese Journal of Applied Physics Rapid Communications   Vol. 55 ( 3 ) page: 030306/1-4   2016.2

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    Using a SiN insertion layer to reduce dislocations, enhanced photovoltaic properties could be obtained in pin InGaN GaN heterojunction solar cell. To investigate the influence of the dislocations on the photovoltaic behaviors, a sample grown without SiN insertion layer was identically prepared for comparison. From optical properties measurements, the reduction in the number of non-radiative centers and a stronger In localization effect was shown in the sample with SiN insertion layer. However, the quantum confined stark effect was almost negligible in both the samples.

  317. Effect of piezoelectric field on carrier dynamics in InGaN-based solar cells Reviewed

    Lee, Seunga; Honda, Yoshio; Amano, Hiroshi

    JOURNAL OF PHYSICS D-APPLIED PHYSICS   Vol. 49 ( 2 ) page: 025103   2016.1

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    To understand the effect of piezoelectric fields on carrier dynamics, we numerically investigated a simple p-GaN/i-InxGa1-xN/n-GaN solar cell structure. A reliable simulation model was obtained by comparing the experimental and simulated results in advance.

  318. Highly elongated vertical GaN nanorod arrays on Si substrates with an AlN seed layer by pulsed-mode metal-organic vapor deposition Reviewed

    Si-Young Bae, Byung Oh Jung, Kaddour Lekhal, Sang Yun Kim, Jeong Yong Lee, Dong-Seon Lee, Manato Deki, Yoshio Honda and Hiroshi Amano

    CrystEngComm   Vol. 18   page: 1505-1514   2016.1

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    . Unlike the thick and high (or middle)-quality GaN templates normally used, nanorod growth was performed on an ultrathin and low-quality AlN/Si platform. Using kinetically controlled growth conditions and a patterning process, exceptionally long GaN nanorods were achieved with high geometric precision.

    DOI: 10.1039/C5CE02056E

  319. The interface analysis of GaN grown on 0° off 6H-SiC with an ultra-thin buffer layer Reviewed

    Zheng Sun, Akio Ohta, Seiichi Miyazaki, Kentaro Nagamatsu, Hojun Lee, Marc Olsson, Zheng Ye, Manato Deki, Yoshio Honda, and Hiroshi Amano

    Japanese Journal of Applied Physics   Vol. 55   page: 010303/1-3   2016.1

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    Previously, we reported a growth method by MOVPE using a single two-dimensional growth step, resulting in 1.2-micron thick crack-free GaN directly grown on 6H-SiC substrate. The introduction of Al-treatment prior to the standard GaN growth step resulted in improved surface wetting of gallium on the SiC substrate.

  320. Growth of GaN on sapphire via low-temperature deposited buffer layer and realization of p-type GaN by Mg doping followed by low-energy electron beam irradiation Invited Reviewed

    Hiroshi Amano

    Rev. Mod. Phys.   Vol. 87 ( 4 ) page: 1133-1138   2015.12

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    This is a personal history of one of the Japanese researchers engaged in developing a method for
    growing GaN on a sapphire substrate, paving the way for the realization of smart television and
    display systems using blue LEDs. The most important work was done in the mid to late 1980s. The
    background to the author's work and the process by which the technology enabling the growth of
    GaN and the realization of p-type GaN was established are reviewed.

  321. Single-crystalline semipolar GaN on Si(001) using a directional sputtered AlN intermediate layer Reviewed

    Tadashi Mitsunari, Ho Jun Lee, Yoshio Honda, Hiroshi Amano

    Journal of Crystal Growth   Vol. 431   page: 60-63   2015.12

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    We obtained single-crystalline semipolar (10View the MathML source1¯3)GaN on a nominal Si(001) substrate with sputtered AlN using the directional feature of sputtering.

    DOI: 10.1016/j.jcrysgro.2015.08.027

  322. Time-resolved photoluminescence properties of hybrids based on inorganic AlGaN/GaN quantum wells and colloidal ZnO nanocrystals Reviewed

    M. Forsberg, C. Hemmingsson, H. Amano, G. Pozina

    Superlattices and Microstructures   Vol. 87   page: 38-41   2015.11

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    Dynamic properties are studied for the AlGaN/GaN quantum well (QW) structures with and without the coating of colloidal ZnO nanocrystals (NCs). The QW exciton recombination rate was reduced in such hybrids compared to the bare QW structure only in the sample with the thinnest cap layer of 3 nm. Assuming that one of the recombination mechanisms in this hybrid is non-radiative resonant energy transfer (NRET) between the QW and the energy acceptor material i.e. ZnO NCs, the maximum pumping efficiency was estimated to be 0.42 at 60 K. The NRET effect is, however, vanished after several months despite that the hybrid structures are composed of chemically stable components.

    DOI: doi:10.1016/j.spmi.2015.07.017

  323. Excitation density dependence of radiative and nonradiative recombination lifetimes in InGaN/GaN multiple quantum wells Reviewed

    Hideaki Murotani, Yoichi Yamada, Yoshio Honda, and Hiroshi Amano

    Physica Status Solidi b   Vol. 252 ( 5 ) page: 940-945   2015.5

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    The optical properties of InGaN/GaN multiple quantum wells (MQWs) have been studied by means of photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy.

    DOI: 10.1002/pssb.201451491

  324. Polarization dilution in a Ga-polar UV-LED to reduce the influence of polarization charges Reviewed

    Toshikiu Yasuda, Kento Hayashi, Syouta Katsuno, Tetsuya Takeuchi, Satoshi Kamiyama, Motoaki Iwaya, Isamu Akasaki, and Hiroshi Amano

    Physica Status Solidi a   Vol. 212 ( 5 ) page: 920-924   2015.5

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    We investigated the influence of polarization charges in nitride-based semiconductors.

    DOI: 10.1002/pssa.201431730

  325. Resonant Raman and FTIR spectra of carbon doped GaN Reviewed

    S. Ito, H. Kobayashi, K. Arak,i, K. Suzuki, N. Sawaki, K. Yamashita, Y. HOnda, H. Amano

    Journal of Crystal Grwoth   Vol. 414 ( 15 ) page: 56-60   2015.3

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    DOI: doi:10.1016/j.jcrysgro.2014.11.024

  326. Electrical characteristics of a-plane low-Mg-doped p-GaN Schottky contacts Reviewed

    Moe Naganawa, Toshichika Aoki, Ji-Su Son, Hiroshi Amano, Kenji Shiojima

    physica status solidi (b)   Vol. 252 ( 5 ) page: 1024–1030   2015.3

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    Electrical characteristics of a variety of Schottky contacts formed with ten metal species on the a-plane of p-type low-Mg-doped GaN grown on r-plane sapphire substrates were studied.

    DOI: 10.1002/pssb.201451581

  327. Optically pumped lasing properties of (1-101) InGaN/GaN stripe multi quantum wells with ridge cavity structure on patterned (001) Si substrates Reviewed

    Maki Kushimoto, Tomoyuki Tanikawa, Yoshio Honda and Hiroshi Amano

    Applied Physics Express   Vol. 8 ( 2 ) page: 022702   2015.2

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    We demonstrated lasing action and investigated the optical properties of (1 (1) over bar 01) multiquantum-well (MQW) stripe crystals on patterned (001) Si substrates. Longitudinal and higher order transverse modes were observed from a ridge waveguide structure. These results strongly suggest the possibility of fabricating (1 (1) over bar 01) InGaN MQW laser diodes on (001) Si. (C) 2015 The Japan Society of Applied Physics

    DOI: doi:10.7567/APEX.8.022702

  328. Dynamic properties of excitons in ZnO/AlGaN/GaN hybrid nanostructures Reviewed

    Mathias Forsberg, Carl Hemmingsson, Hiroshi Amano , Galia Pozina

    Scientific Reports   Vol. 5   page: 7889   2015.1

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    III-nitride semiconductor/organic polymer hybrid heterostructures combine advantages of epitaxially grown semiconductor quantum wells (QW) with inexpensive polymers having efficient luminescence in the visible region1. Such hybrid micro-structured light emitting diodes (LED) are promising for fabrication of low-cost and highly efficient microlight sources that can be used in full-color displays, imaging systems, miniature chemical and biological sensors. In typical polyfluorene/GaN-based LED hybrids, UV emission from a GaN heterostructure down converts to the organic polymer fluorescence in the visible region via a radiative energy transfer. Overlapping between the UV luminescence and the polyfluorene absorption is required for the operation
    of these hybrids. Today, a novel class of hybrid structures is suggested, in which a non-radiative resonant energy transfer (NRET) from excitation generated in inorganic QWs to excitons in organic films can be utilized. Such LEDs might be considerably more efficient than their radiative energy transfer analogues. In addition to the necessity of a significant spectral overlap between the QW emission and the polymer absorption spectrum, these devices require that the two materials are placed in a close interaction distance of a few nm. The bottleneck is that the operation lifetime of organic/semiconductor hybrid LED structures is limited by degradation
    of polyfluorenes. Using colloidal semiconductor nanocrystals (NCs) instead of polymers can significantly improve the lifetime of such devices. In addition to superior luminescence properties, relatively low cost and chemical stability, the spectral tunability can be achieved by changing the particle chemistry and size. The efficiency of non-radiative resonance energy transfer is typically determined using transient photoluminescence
    (PL) measurements from the quenching of the QW exciton lifetime in the presence of acceptor material (i.e.
    colloidal NCs or polyfluorene). It might be correct in assumption that NRET is the only additional recombination channel appearing in hybrids compared to the bareQWstructure. However, other factors can play also a significant role. For example, surface potential effects have to be considered when non-radiative resonant energy transfer is measured using dynamic properties of the QW excitons.
    Thus, in this work we have studied and discussed the possibility of NRET in hybrid structures fabricated using ZnO NCs films coated on the top of the AlGaN/GaN QWs samples. ZnO NCs satisfies the requirement of
    absorption overlapping with GaN emission (a room temperature band gap energy is 3.3 and 3.4 eV for ZnO and GaN, respectively). Dynamic properties ofQWexcitons in the hybrids and in the bareQWsamples are analyzed in dependence on the QWs cap layer thickness.

    DOI: doi:10.1038/srep07889

  329. Development of underfilling and encapsulation for deep-ultraviolet LEDs Reviewed

    Kiho Yamada, Yuuta Furusawa, Shoko Nagai, Akira Hirano, Masamichi Ippommatsu, Ko Aosaki, Naoki Morishima, Hiroshi Amano and Isamu Akasaki

    Applied Physics Express   Vol. 8 ( 1 ) page: 012101   2015.1

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    The currently available resins for underfilling and encapsulation are limited to wavelengths longer than approximately 330 nm because almost all resins are decomposed by deep-ultraviolet light. Fluorine resins are possible materials for underfilling and encapsulation in deep-ultraviolet LEDs, and we have investigated methods of underfilling and encapsulation using such resins. Also, their durability at wavelengths of 265 and 285 nm has been studied from the photochemical viewpoint, and we propose a stable amorphous fluorine resin that is optically isotropic. Also, a trial of encapsulation using the resin has been made.

    DOI: doi:10.7567/APEX.8.012101

  330. Highly ordered catalyst-free InGaN/GaN core-shell architecture arrays with expanded active area region Reviewed

    Jung, Byung Oh; Bae Si-Young; Kim, Sang Yun; Lee, Seunga; Lee, Jeong Yong; Lee, Dong-Seon; Kato, Yoshihiro; Honda, Yoshio ;Amano, Hiroshi

    Nano Energy   Vol. 11   page: 294-303   2015.1

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    Highly ordered, position-controlled gallium nitride (GaN) nanowire based multiple-quantum-wells (MQWs) core-shell architecture arrays are synthesized by metalorganic chemical vapor deposition (MOCVD). We investigate the possibility of using GaN nanowire arrays as a basal template for the growth of InxGa1-xN/GaN MQWs. The MQWs on three different crystal facets (c(-), m(-), and semipolar-plane) of GaN nanowire exhibit dissimilar structural properties. The structural characteristics of InGaN/GaN core-shell arrays are inspected by cross-sectional high-resolution transmission electron microscopy (HR-TEM). We also investigate the optical properties of MQW core-shell structure nanoarrays. The luminescent characteristics of InGaN/GaN core-shell structure arrays are determined by photoluminescence (PL) and cathodoluminescence (CL) measurements. The monochromatic CL images clearly show the light emission behavior of InGaN/GaN MQW coaxial structure. Two distinguishable light emission peaks were observed in the GaN nanowire based core-shell structure. The characteristic of light emission mainly depends on the properties of MQWs, which are generated from different crystal facets of GaN. In addition, the light emission intensity shows different behaviors depending on the area of the GaN nanowire m-plane. The results of this study suggest that GaN nanowire arrays can be used as a good alternative basal template for next-generation light-emitting diodes (LEDs).

    DOI: DOI: 10.1016/j.nanoen.2014.11.003

  331. Continuous in situ X-ray reflectivity investigation on epitaxial growth of InGaN by metalorganic vapor phase epitaxy Reviewed

    Guangxu Ju, Shingo Fuchi, Masao Tabuchi, Hiroshi Amano, Isamu Akasaki

    Journal of Crystal Growth   Vol. 407   page: 68-73   2014.12

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    Continuous in situ X-rayreflectivity(XRR)measurementswereusedtoinvestigatethegrowthprocessof
    an In0.11Ga0.89N epilayeranditssinglequantumwellgrownonc-planeGaN/sapphiretemplatesusingan
    in-house-designed metalorganicvaporphaseepitaxyinstalledinalaboratory-gradeX-raydiffract-
    ometer.Thesurfacerougheningoftheepilayerasafunctionofgrowthtimewascalculatedfromthe
    continuous in situ XRR curve.Thegrowthrate,criticalthickness hc(r) for surfaceroughening,and
    roughening ratewereobtained.Theexperimentalcriticalthickness hc(r) of theIn0.11Ga0.89N epilayer
    analyzed fromthecontinuous in situ XRR curvewas14.870.4 nm.Basedonthecalculatedtheoretical
    critical thickness hc and theexperimental hc(r,2), Fischer's modelseemstobeappropriatefordescribing
    the criticalthicknessoftheInGaN/GaN.

    DOI: 10.1016/j.jcrysgro.2014.08.023

  332. Photoemission lifetime of a negative electron affinity gallium nitride photocathode Reviewed

    Tomohiro Nishitani, Masao Tabuchi, Hiroshi Amano, Takuya Maekawa, Makoto Kuwahara and Takashi Meguro

    Journal of Vacuum Science and Technology   Vol. B32 ( 6 ) page: 06F901   2014.11

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    A photocathode electron source using p-type GaN semiconductor with a negative electron affinity (NEA) surface has been studied for its ability to maintain an extended NEA state. The key technology of NEA photocathodes is the formation of electric dipoles by cesium and gallium atoms on the surface, which makes it possible for photoexcited electrons in the conduction band minimum to escape into the vacuum. This means that in order to keep the electron energy spread as small as possible, the excitation photon energy should be tuned to the band gap energy. However, the NEA surface is damaged by the adsorption of residual gas and the back-bombardment of ionized residual gas by photoelectrons. The p-type GaN semiconductor was measured time evolution in quantum yield during NEA surface activation, and a lifetime of quantum yield of excitation energy corresponding to the band gap energy in comparison to the p-type GaAs as the conventional NEA photocathode. In NEA surface activation process, the quantum yield of the GaN was more than 3 orders of magnitude higher than that of the GaAs by only cesium deposition. The exposure amount of cesium in the NEA surface activation of the GaAs was 1.5 times as that of the GaN, even though the quantum yield of the GaAs was the same value as the GaN. Lifetime of NEA-photocathodes using the GaN was 21 times longer than that using the GaAs. The decrease of quantum yield of the GaAs was well correlated in the form of the exponential decrease function with a decrease time of 4.4 h, while the decrease of quantum yield of the GaN was well correlated in the form of the exponential decrease function with two decrease times of 47 and 174 h.

  333. Nature of yellow luminescence band in GaN grown on Si substrate Reviewed

    Shogo Ito, Taihei Nakagita, Nobuhiko Sawaki, Hyung Soo Ahn, Masashi Irie, Toshiki Hikosaka, Yoshio Honda, Masahito Yamaguchi and Hiroshi Amano

    Japanese Journal of Applied Physics   Vol. 53   page: 11RC02/1-5   2014.9

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    DOI: doi:10.7567/JJAP.53.11RC02

  334. Atom probe tomography study of Mg-doped GaN layers Reviewed

    S Khromov, D Gregorius, R Schiller, J Lösch, M Wahl, M Kopnarski, H Amano, B Monemar, L Hultman and G Pozina

    Nanotechnology   Vol. 25 ( 27 )   2014.6

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    DOI: doi:10.1088/0957-4484/25/27/275701

  335. Characterization of nonpolar a-plane InGaN/GaN multiple quantum well Reviewed

    Ji-Su Son, Yoshio Honda, Masahito Yamaguchi and Hiroshi Amano

    Japanese Journal of Applied Physics   Vol. 53   page: 05FL01   2014.5

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    The characteristics of nonpolar a-plane (1120) GaN (a-GaN) grown using single and double nanopillar SiO2 masks were investigated. The two
    nanopillar SiO2 masks were directly fabricated on an r-plane sapphire substrate and a-GaN by the epitaxial lateral overgrowth (ELOG) technique.
    Through the use of the single and double nanopillar SiO2 masks, the crystalline quality and optical properties of a-GaN were markedly improved
    because of the nanoscale ELOG effect and a number of voids in the single and double nanopillar SiO2 mask areas in comparison with the planar
    sample. The submicron pit densities of the planar, single, and double nanopillar mask samples were >2 ' e9, >7e8, and >4e8cm-2,
    respectively. The internal quantum efficiency (IQE) values at room temperature of three-period InGaN/GaN multiple quantum wells (MQWs) grown
    using the planar, single, and double nanopillar masks were 45, 60, and 68% at a carrier concentration of 1.0e18cm-3, respectively.

    DOI: 10.7567/JJAP.53.05FL01

  336. X-ray investigations of GaInN single quantum wells grown by atomic layer epitaxy and metalorganic vapor phase epitaxy Reviewed

    Guangxu Ju, Yoshihiro Kato, Yoshio Honda, Masao Tabuchi, Yoshikazu Takeda, and Hiroshi Amano

    physica status solidi (c)   Vol. 11 ( 3-4 ) page: 393-396   2014.4

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    A set of GaN/GaInN single quantum wells (SQWs) were grown on c-plane GaN/sapphire templates using metal organic vapor phase epitaxy (MOVPE) and atomic layer epitaxy (ALE). The structural information on the interfaces and surfaces was obtained by fitting the experimental X-ray spectra and was compared between MOVPE and ALE mode. The X-ray crystal truncation rod (CTR) scattering measurement results showed that the samples grown by ALE had sharper interfaces than those grown by MOVPE. Both the X-ray reflectivity (XRR) curve-fitting results and atomic force microscope (AFM) results indicated that the surfaces of the ALE-grown SQWs were smoother than those of MOVPE-grown SQWs.

    DOI: 10.1002/pssc.201300670

  337. Enhancement of light output power on GaN based light emitting diodes using two direction stripe patterned sapphire substrate Reviewed

    Okuno, Koji; Oshio, Takahide; Shibata, Naoki; Honda, Yoshio; Yamaguchi, Masahito; Amano, Hiroshi

    Physica Status Solidi C   Vol. 11   page: 722-725   2014.4

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    To achieve both the reduction of threading dislocation density (TDD) and the enhancement of light extraction efficiency (LEE) of light-emitting diodes (LEDs), a two-directional stripe-patterned sapphire substrate (TPSS) was fabricated. First, a stripe pattern parallel to the a-axis of Al2O3 was formed on an as-received c -sapphire wafer and then a second stripe pattern rotated around 3° from the m-axis of Al2O3 was formed on the first stripe PSS. The light output power of TPSS LEDs was around 1.25 times higher than that of LEDs on a flat sapphire substrate. This enhancement is caused by the increase of both the internal quantum efficiency (IQE) and the LEE. On the other hand, although the LED on TPSS with the second stripe just parallel to the m-axis of Al2O3 showed a similar enhancement ratio of the light output power, the current leakage of this LED increased with the concentration of threading dislocations on the surface of LEDs. Stripes rotated 3° from the m-axis of Al2O3 changed the growth mode and realized GaN films with a smooth surface without pit formation. Therefore, the misalignment of the stripe from the m-axis of Al2O3 will become a new design parameter for realizing high-efficiency reliable LEDs.

    DOI: 10.1002/pssc.201300470

  338. Epitaxial growth of GaN by REMOCVD in the downflow of a very high frequency(VHF) N2/H2 excited plasma Reviewed

    Yi Lu, Hiroki Kondo,Kenji Ishikawa,Osamu Oda,KeigoTakeda,Makoto Sekine, Hiroshi Amano,Masaru Hori

    Journal of Crystal Growth   Vol. 391   page: 97-103   2014.4

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    We found that this REMOCVD allowed the growth of epitaxial GaN films of the wurtzite structure of (0001) orientation on sapphire substrates with a high growth rate of 0.42 μm/h at a low temperature of 800 °C. The present REMOCVD is a promising method for GaN growth at relatively low temperature and without using costly ammonia gas.

    DOI: 10.1016/j.jcrysgro.2014.01.014

  339. Growth of InGaN/GaN multiple quantum wells on size-controllable nanopyramid arrays Reviewed

    Cao Miao, Yoshio Honda, Masahito Yamaguchi and Hiroshi Amano

    Japanese Journal of Applied Physics   Vol. 53   page: 0303060   2014.3

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    Regularly distributed nanopyramid arrays with a highly uniform size were grown by selective-area growth. The nanopyramid size could be tuned by varying the growth time. Two emission peaks were observed from multiple quantum wells grown on the nanopyramids. The longer-wavelength peak originated from the apexes of pyramids with threefold symmetry. High-density stacking faults observed at these triangular apexes might be responsible for the higher indium incorporation. The formation of embedded voids inside the pyramids was explained by the different growth rates at the edge and center of the mask window caused by the low diffusion length.

    DOI: 10.7567/JJAP.53.030306

  340. In situ X-ray investigation of changing barrier growth temperatures on InGaN single quantum wells in metal-organic vapor phase epitaxy Reviewed

    Guangxu Ju, Yoshio Honda, Masao Tabuchi, Yoshikazu Takeda, and Hiroshi Amano

    Journal of Applied Physics   Vol. 115   page: 094906   2014.3

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    The effects of GaN quantum barriers with changing growth temperatures on the interfacial
    characteristics of GaN/InGaN single quantum well (SQW) grown on GaN templates by metalorganic
    vapour phase epitaxy were in situ investigated by X-ray crystal truncation rod (CTR) scattering and
    X-ray reflectivity measurements at growth temperature using a laboratory level X-ray diffractometer.
    Comparing the curve-fitting results of X-ray CTR scattering spectra obtained at growth temperature
    with that at room temperature, the InxGa1-xN with indium composition less than 0.11 was stabile of
    the indium distribution at the interface during the whole growth processes.

    DOI: 10.1063/1.4867640

  341. Multijunction GaInN-based solar cells using a tunnel junction Reviewed

    Hironori Kurokawa, Mitsuru Kaga, Tomomi Goda, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki and Hiroshi Amano

    Applied Physics Express   Vol. 7 ( 3 ) page: 034104   2014.3

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    We fabricated and characterized a two-junction GaInN-based solar cell using a tunnel junction fabricated by crystal growth. This solar cell has two active layers with a differing bandgap energy corresponding to blue or green light. We confirmed that the open-circuit voltage (VOC) in this solar cell was increased by the series connection using the tunnel junction. The short-circuit current density, VOC, fill factor, and energy conversion efficiency of this solar cell were 0.28 mA/cm2, 3.0 V, 0.5, and 0.41%, respectively, under an air mass filter of 1.5 G at 1-sun irradiation and room temperature.

    DOI: 10.7567/APEX.7.034104

  342. Novel activation process for Mg-implanted GaN Reviewed

    Shin Hashimoto, Takao Nakamura, Yoshio Honda, Hiroshi Amano

    Journal of Crystal Growth   Vol. 388   page: 112-115   2014.2

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    A novel activation process for Mg-implanted GaN was demonstrated. As opposed to the conventional thermal annealing process, an H2/NH3 alternating supply annealing process achieved better optical activation, stronger near-ultraviolet luminescence and weaker yellow luminescence in the photoluminescence spectroscopy. After this process, small hexagonal hillocks were observed on the surface, which indicated that crystal regrowth was induced by this process, consisting of decomposition of GaN by H2 supplies and re-crystallization by NH3 supplies. It was revealed that the implanted Mg could easily be located at the activation site by means of crystal regrowth by this process.

    DOI: doi:10.1016/j.jcrysgro.2013.07.011

  343. Properties of the main Mg-related acceptors in GaN from optical and structural studies Reviewed

    B. Monemar, P. P. Paskov, G. Pozina, C. Hemmingsson, J. P. Bergman, S. Khromov, V. N. Izyumskaya, V. Avrutin, X. Li, H. Morkoç, H. Amano, M. Iwaya, and I. Akasaki

    Journal of Applied Physics   Vol. 115   page: 053507   2014.2

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    The luminescent properties of Mg-doped GaN have recently received particular attention, e.g., in the
    light of new theoretical calculations, where the deep 2.9 eV luminescence band was suggested to be
    the main optical signature of the substitutional MgGa acceptor, thus, having a rather large binding
    energy and a strong phonon coupling in optical transitions. We present new experimental data on
    homoepitaxial Mg-doped layers, which together with the previous collection of data give an
    improved experimental picture of the various luminescence features in Mg-doped GaN.

    DOI: 10.1063/1.4862928

  344. Growth of low-defect-density nonpolar a-plane GaN on r-plane sapphire using pulse NH3 interrupted etching Reviewed

    Ji-Su Son, Yoshio Honda, and Hiroshi Amano

    Optics Express   Vol. 22 ( 3 ) page: 3585-3592   2014.2

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    Nonpolar a-plane (11-20) GaN (a-GaN) layers with low overall defect density and high crystalline quality were grown on r-plane sapphire substrates using etched a-GaN. The a-GaN layer was etched by pulse NH3 interrupted etching.

    DOI: 10.1364/OE.22.003585

  345. Morphology development of GaN nanowires using a pulsed-mode MOCVD growth technique Reviewed

    Byung Oh Jung, Si-Young Bae, Yoshihiro Kato, Masataka Imura, Dong-Seon Lee, Yoshio Honda and Hiroshi Amano

    CrystEngComm   Vol. 16   page: 2273-2282   2014.1

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    we demonstrate a scalable process for the precise position-controlled selective growth of
    GaN nanowire arrays by metalorganic chemical vapor deposition (MOCVD) using a pulsed-mode growth
    technique. The location, orientation, length, and diameter of each GaN nanowire are controlled via
    pulsed-mode growth parameters such as growth temperature and precursor injection and interruption
    durations.

    DOI: 10.1039/c3ce42266f

  346. Characteristics of a-plane GaN films grown on optimized silicon-dioxide-patterned r-plane sapphire substrates Reviewed

    Ji-Su Son, Y. Honda, M. Yamaguchi, H. Amano, K. H. Baik, Y. G. Seo and S. M. Hwang

    Thin Solid Films   Vol. 546 ( 11 ) page: 108-113   2013.11

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    We report on the characteristics of a-plane GaN films directly grown on optimized silicon-dioxide-patterned r-plane sapphire substrates. Various shapes and sizes of silicon dioxide patterns were considered with the aim of achieving fully coalescent a-plane GaN films with a smooth surface and high crystalline quality. The omega full widths at half maximum of the X-ray rocking curve values of optimized a-plane GaN films with regular hexagonal patterns of 1 micron window width and 6 micron mask width were measured to be 597 arcsec along the c-axis direction and 457 arcsec along the m-axis direction. Atomic force microscopy images revealed a significant reduction in the density of submicron pits in the mask region.

  347. Effects of exciton localization on internal quantum efficiency of InGaN nanowires Reviewed

    Hideaki Murotani, Yoichi Yamada, Takuya Tabata, Yoshio Honda, Masahito Yamaguchi and Hiroshi Amano

    Journal of Applied Physics   Vol. 114   page: 153506   2013.10

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    Internal quantum efficiency of InGaN nanowires grown by PA MBE was investigated in detail.

    DOI: 10.1063/1.4825124

  348. Strain-Compensated Effect on the Growth of InGaN/AlGaN Multi-Quantum Well by Metalorganic Vapor Phase Epitaxy Reviewed

    Tomohiro Doi, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JB14   2013.8

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    InGaN/AlGaN multi-quantum wells (MQWs) were grown by metalorganic vapor phase epitaxy. The In composition of the InGaN well layer was found to increase with the tensile strain of the AlGaN barrier layer. The InGaN/AlGaN strain-compensated structure can be grown at a higher growth temperature than that of the InGaN/GaN MQW, which shows that the same emission wavelength and thus the density of the V-defects can be effectively suppressed.

    DOI: 10.7567/JJAP.52.08JB14

  349. GaN Overgrowth on Thermally Etched Nanoporous GaN Template Reviewed

    Cao Miao, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JB03   2013.8

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    A thermal-etching process for fabricating nanoporous GaN templates in a metalorganic vapor phase epitaxy (MOVPE) reactor was proposed. Such nanoporous templates exhibited nearly complete strain relaxation and considerably increased photoluminescence (PL) intensity. The threading dislocation density (TDD) after overgrowth was reduced from 3 ×109 to 4 ×108 cm-2 for the template with poor quality, whereas little improvement was observed for the high-quality template (TDD, 4 ×108 cm-2). Multiple quantum wells (MQWs) grown on a nanoporous template fabricated from the high-quality GaN template were used to assess the effect on LED performance. The PL intensity of the sample with a nanoporous structure showed a twofold increase in PL intensity compared with the control sample.

    DOI: 10.7567/JJAP.52.08JB03

  350. Growth of GaN on Si(111) Substrates via a Reactive-Sputter-Deposited AlN Intermediate Layer Reviewed

    Takaya Yamada, Tomoyuki Tanikawa, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

    Japanese Journal of Applied Physics   Vol. 52   page: 08JB16   2013.8

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    GaN films were successfully grown on Si(111) substrates using a reactive-sputter-deposited AlN intermediate layer (sp-AlN) at 350 °C. Uniform GaN growth was obtained with the pre sputtering of a thin Al film before the deposition of sp-AlN. Atomic force microscopy (AFM) measurements revealed that the density of pits originating from the ends of mixed/screw-type dislocations is about 109 cm-2, which is much lower than that of GaN grown on a metalorganic vapor phase epitaxy (MOVPE) deposited AlN intermediate layer. The decrease in the pit density might have originated from the small number of initial nuclei of GaN.

    DOI: 10.7567/JJAP.52.08JB16

  351. Fabrication of InGaN/GaN Multiple Quantum Wells on (1-101) GaN Reviewed

    Tomoyuki Tanikawa, Tomotaka Sano, Maki Kushimoto, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JC05   2013.8

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    InGaN/GaN multiple quantum wells (MQWs) on semipolar (1101) GaN microstripes on a Si substrate were fabricated and their optical properties were investigated. From cathodoluminescence (CL) analysis, strong CL emission was obtained in an MQW emitting at 433 nm. However, dark lines appeared in MQWs emitting at longer wavelengths. These dark lines are attributed to lattice relaxation and the generation of misfit dislocations and stacking faults in an MQW, resulting in nonradiative centers. The internal quantum efficiency (IQE) was estimated from excitation-power-dependent photoluminescence analysis. The (1101) InGaN/GaN MQW had a high IQE owing to the high crystalline quality of the underlying GaN and the reduced piezoelectric field. The IQE at a carrier concentration of 1×1018 cm-3 in a sample emitting at 490 nm was as high as 90%. The efficiency decreased in a sample with a higher indium content in the MQW due to the generation of misfit dislocations and stacking faults.

    DOI: 10.7567/JJAP.52.08JC05

  352. Stacking Faults and Luminescence Property of InGaN Nanowires Reviewed

    Takuya Tabata, Jihyun Paek, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JE06   2013.8

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    InGaN nanowires (NWs) were grown on (111)Si substrate using radio-frequency plasma-assisted molecular beam epitaxy, and the density of the stacking faults (SFs) in the InGaN NWs was estimated. High-density SFs were observed in the scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM) images of the InGaN NWs, and a few zincblende layers appeared in the wurtzite structure. When growth temperature increased, the density of the SFs in the InGaN NW, the photoluminescence (PL) peak wavelength, and the full width at half maximum (FWHM) of PL spectra decreased, whereas the integrated PL intensity increased. These results suggest that a high growth temperature is effective for decreasing the density of SFs in InGaN NWs, and InGaN NWs grown at high temperature have strong PL luminescence due to the low In composition and the corresponding low SFs density.

    DOI: 10.7567/JJAP.52.08JE06

  353. Effects of Nano- and Microscale SiO2 Masks on the Growth of a-Plane GaN Layers on r-Plane Sapphire Reviewed

    Ji-Su Son, Cao Miao, Yoshio Honda, Masahito Yamaguchi, Hiroshi Amano, Yong Gon Seo, Sung-Min Hwang, and Kwang Hyeon Baik

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JC04   2013.8

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    We report on the combined effects of a-plane GaN layers on a nanoscale patterned insulator on an r-plane sapphire substrate and epitaxial lateral overgrowth (ELOG) techniques. The fully coalescent a-plane GaN layer using nano- and microscale SiO2 masks showed the formation of nano- and microscale voids on the masks, respectively. Atomic force microscopy (AFM) measurements revealed a surface roughness of 0.63 nm and a submicron pit density of 7.8 ×107 cm-2. Photoluminescence (PL) intensity was enhanced by a factor of 9.0 in comparison with that of a planar sample. Omega full-width at half-maximum (FWHM) values of the (1120) X-ray rocking curve along the c- and m-axes were 553 and 788 arcsec, respectively. A plan-view cathodoluminescence (CL) mapping image showed high luminescence intensity on the SiO2 masks.

    DOI: 10.7567/JJAP.52.08JC04

  354. High Internal Quantum Efficiency Blue-Green Light-Emitting Diode with Small Efficiency Droop Fabricated on Low Dislocation Density GaN Substrate Reviewed

    Tomotaka Sano, Tomohiro Doi, Shunko Albano Inada, Tomohiko Sugiyama, Yoshio Honda, Hiroshi Amano, and Takashi Yoshino

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JK09   2013.8

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    We fabricated blue, blue-green, and green light-emitting diodes (LEDs) of different dislocation densities (DD) and characterized their internal quantum efficiency (IQE). The IQE of the blue LEDs fabricated using GaN substrate exceeded 90 percent, however, when we used a GaN-on-sapphire substrate, IQE was limited to 60 percent. Droop was reduced by use of the GaN substrate. The junction temperature of the GaN-on-sapphire substrate was found to be 200 degreeC although the junction temperature of the GaN substrate was 50 degreeC when a forward current of 100 A/cm2 was driven. A lowering of IQE in green LEDs to 60 percent was observed, even though we used a low-dislocation-density substrate.The junction temperature of blue-green and green LEDs was about 100 degreeC when a forward current of 177 A/cm2 was driven, which indicated that junction temperature is not a major factor for IQE suppression in green LEDs.

    DOI: 10.7567/JJAP.52.08JK09

  355. Growth Mode and Threading Dislocation Behavior of GaN Films Grown on Patterned Sapphire Substrate with Radial Stripe Pattern Reviewed

    Koji Okuno, Takahide Oshio, Naoki Shibata, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JB09   2013.8

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    A sapphire substrate with a grooved stripe pattern along different radial directions was prepared to investigate the effects of stripe direction on the growth mode and threading dislocation (TD) behavior of GaN films. When the stripe direction is oriented parallel to [1010]sapphire, the GaN films have a triangular structure that is formed by the GaN{1011} facets. As the stripe direction rotates from [1010]sapphire, nanosteps with a step height of around 80 nm are formed on the GaN{1011} facets and then the coalescence of GaN on the ridges and grooves advances. GaN films with a smooth surface and a TD density as low as 2.0×108 cm-2 were achieved when the stripe direction was rotated 3° from [1010]sapphire. Our result indicates that the surface roughness and TD density of GaN films can be controlled by precisely adjusting the angle of the stripe direction from [1010]sapphire.

    DOI: 10.7567/JJAP.52.08JB09

  356. Thick InGaN Growth by Metal Organic Vapor Phase Epitaxy with Sputtered InGaN Buffer Layer Reviewed

    Toshiya Ohata, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JB11   2013.8

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    A thick InGaN film was grown on a sapphire substrate by metal organic vapor phase epitaxy using a thin buffer layer of sputter-deposited InGaN. A thick film of highly luminescent In0.2Ga0.8N can be successfully grown at a rate as high as 2 µm/h. The crystal quality of InGaN grown on the sputter-deposited InGaN buffer layer was better than that of InGaN grown directly on the sapphire substrate. The sample showed n-type conduction with a carrier concentration and mobility of 5×1018 cm-3 and 3 cm2/(V·s), respectively.

    DOI: 10.7567/JJAP.52.08JB11

  357. Combination of ITO and SiO2/AlN Dielectric Multilayer Reflective Electrodes for UV-Emitting Diodes Reviewed

    Tsubasa Nakashima, Kenichiro Takeda, Hiroshi Shinzato, Motoaki Iwaya, Satoshi Kamiyama, Tetsuya Takeuchi, Isamu Akasaki, and Hiroshi Amano

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JG07   2013.8

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    We have investigated novel reflective electrodes by combining an ITO layer and a SiO2/AlN dielectric multilayer (DM) for UV-light-emitting diodes (LEDs). The reflectance of 10 pairs of SiO2/AlN DM reached 98.5 percent at 350 nm. As a result, the ITO/DM electrodes simultaneously satisfied the requirements of high reflectivity in the UV region, good contact characteristics, and current spreading. The light output power of the UV LED with an ITO/DM electrode is 1.2 and 1.6 times higher than those of LEDs with ITO/Al and Ni/Au electrodes, respectively.

    DOI: 10.7567/JJAP.52.08JG07

  358. GaN Nanowires Grown on a Graphite Substrate by Radio Frequency Molecular Beam Epitaxy Reviewed

    Shinta Nakagawa, Takuya Tabata, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JE07   2013.8

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    Self-assembled GaN and InGaN nanowires (NWs) were directly grown on a highly oriented pyrolytic graphite (HOPG) substrate by radio frequency molecular beam epitaxy (RF-MBE). The GaN NWs grown on HOPG had a shorter length and larger diameter than those grown conventionally on a Si(111) substrate based on the analysis of scanning electron microscopy (SEM) images. They were also found to have good crystalline qualities with few stacking faults, as determined by scanning transmission electron microscopy (STEM) analysis. Photoluminescence (PL) measurements at room temperature indicated that the luminescence intensity of the GaN NWs on HOPG is stronger than that of NWs grown on a Si(111) substrate; however, the InGaN NWs on both substrates showed similar tendencies with respect to the shift of the luminescence wavelength as a function of the growth temperature. While In incorporation decreased as the growth temperature increased, the uniformity of the InGaN NW arrays improved rapidly.

    DOI: 10.7567/JJAP.52.08JE07

  359. Concentrating Properties of Nitride-Based Solar Cells Using Different Electrodes Reviewed

    Mikiko Mori, Shinichiro Kondo, Shota Yamamoto, Tatsuro Nakao1, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki, and Hiroshi Amano

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JH02   2013.8

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    We investigated the concentration properties of GaInN-based solar cells using different window electrodes. A significant difference was observed between the concentrating properties of the window electrode structures. It was clearly found that indium tin oxide (ITO) is suitable as an electrode. The short-circuit current density, open-circuit voltage, fill factor, and energy conversion efficiency of nitride-based solar cells fabricated using an ITO electrode were 7.1×102 mA/cm2, 2.2 V, 79%, and 4.0%, respectively, under an air mass filter of 1.5G at 300 suns and at room temperature.

    DOI: 10.7567/JJAP.52.08JH02

  360. Emission Wavelength Dependence of Internal Quantum Efficiency in InGaN Nanowires Reviewed

    Hideaki Murotani, Hiroya Andoh, Takehiko Tsukamoto, Toko Sugiura, Yoichi Yamada, Takuya Tabata, Yoshio Honda, Masatoshi Yamaguchi, and Hiroshi Amano

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JE10   2013.8

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    The internal quantum efficiency (IQE) of InGaN nanowires with different emission wavelength of 485, 515, 555, and 580 nm has been studied by means of photoluminescence (PL) spectroscopy. It was found from the analysis of IQE as a function of excitation power density that the IQE was unchanged at about 100% under weak excitation conditions at low temperature. This indicated that the effects of nonradiative recombination processes were negligibly small at low temperature. Moreover, the IQE increased from 5 to 12% with increasing emission wavelength from 485 to 580 nm. Since the clear correlation between the IQE and the PL blue shift due to band filling effects of localized states was observed, the increase in the IQE reflected the increase in the effect of exciton localization with increasing indium composition.

    DOI: 10.7567/JJAP.52.08JE10

  361. Luminescence of Acceptors in Mg-Doped GaN Reviewed

    Bo Monemar, Sergey Khromov, Galia Pozina, Plamen Paskov, Peder Bergman, Carl Hemmingsson, Lars Hultman, Hiroshi Amano, Vitaliy Avrutin, Xing Li, and Hadis Morkoç

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JJ03   2013.8

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    It is concluded that the typical PL peaks at 3.466 eV (ABE1)and the broader 3.27 eV DAP PL are the expected standard PL signatures of the substitutional Mg acceptor. Additional broader peaks at 3.455 eV (ABE2) and 3.1 eV are suggested to be related to the same acceptors perturbed by nearby basal plane stacking faults. The low temperature metastability of PL spectra is assigned to a nonradiative metastable deep level.

    DOI: 10.7567/JJAP.52.08JJ03

  362. Analysis of Broken Symmetry in Convergent-Beam Electron Diffraction along <11-20 > and <1-100 > Zone-Axes of AlN for Polarity Determination Reviewed

    Masataka Imura, Ujjal Gautam, Kiyomi Nakajima, Yasuo Koide, Hiroshi Amano, and Kenji Tsuda

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JE15   2013.8

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    To accurately and easily determine the polarity of AlN using transmission electron microscopy, we compare the convergent-beam electron diffraction (CBED) patterns along the widely used <1120 > and <1100 > zone-axes. For the <1120 > zone-axis, the diffraction disk of g= 0002 differs from that of g= 0002, while for <1100 >, the diffraction disks of g= 0002 and 0002 are similar. The preferential clarity of these two disks is explained using Bloch-wave dynamical theory. To further support the explanation, we compare the results of GaN case. On the basis of our analysis, we conclude that the CBED patterns of the <1120 > zone-axis are more useful for accurately determining AlN polarity compared to the CBED patterns along the <1100 > zone-axis.

    DOI: 10.7567/JJAP.52.08JE15

  363. Microstructure Analysis of AlGaN on AlN Underlying Layers with Different Threading Dislocation Densities Reviewed

    Kimiyasu Ide, Yuko Matsubara, Motoaki Iwaya, Satoshi Kamiyama, Tetsuya Takeuchi, Isamu Akasaki, and Hiroshi Amano

    Jpn. J. Appl. Phys.   Vol. 52 ( 8 ) page: 08JE22   2013.8

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    Using the epitaxial lateral growth technique, we compared the crystallinity and relaxation ratio of 3-µm- and 200-nm-thick Al0.5Ga0.5N on an AlN template and AlN grown by epitaxial lateral overgrowth (ELO-AlN), both of which were grown on a sapphire substrate. Although the relaxation ratios of 3-µm-thick Al0.5Ga0.5N were almost the same, the misfit dislocation density at the interface and the density of threading dislocations reaching the surface of Al0.5Ga0.5N were significantly different. Also, the increase in the density of newly generated misfit dislocations was found to be highly dependent on the quality of the AlN underlying layer. We also discuss the difference in the initial growth mode of each Al0.5Ga0.5N sample.

    DOI: 10.7567/JJAP.52.08JE22

  364. Progress and Prospect of the Growth of Wide-Band-Gap Group III Nitrides: Development of the Growth Method for Single-Crystal Bulk GaN Reviewed

    Hiroshi Amano

    Japanese journal of applied physics   Vol. 52 ( 5 ) page: 050001-1-050001-10   2013.5

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    With the continuously increasing demand for the conservation and generation of energy, bulk substrates of group III nitride semiconductors are highly expected to maximize their potential. In this report, I review the current status of the growth methods for bulk GaN single crystals used for substrates as well as summarize the characteristics of blue light-emitting diodes (LEDs), heterojunction field-effect transistors (HFETs), and photovoltaic cells on GaN substrates.

    DOI: 10.7567/JJAP.52.050001

  365. AlN/air distributed Bragg reflector by GaN sublimation from microcracks of AlN Reviewed

    T. Mitsunari, T. Tanikawa, Y. Honda, M. Yamaguchi, H. Amano

    Journal of Crystal Growth   Vol. 370 ( 1 ) page: 16-21   2013.5

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    The GaN/AlN multilayer structure was grown on a stripe-patterned and dot-patterned Si substrate, and subsequently annealed at 1200 °C in H2 and NH3 atmosphere. We achieved an AlN/air structure by the decomposition of GaN from the microcracks of AlN. Partially crack-free AlN layers were observed over a 5×5 μm area in the c-plane of AlN/air DBRs.

    DOI: 10.1016/j.jcrysgro.2012.09.062

  366. Structural evolution of AlN buffer and crystal quality of GaN films on a- and c-sapphire grown by metalorganic vapor phase epitaxy Reviewed

    Okuno, Koji; Oshio, Takahide; Shibata, Naoki; Honda, Yoshio; Yamaguchi, Masahito; Tanaka, Shigeyasu; Amano, Hiroshi

    Physica Status Solidi C   Vol. 10 ( 3 ) page: 369-372   2013.3

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    DOI: 0.1002/pssc.201200587

  367. Effects of low energy e-beam irradiation on cathodoluminescence from GaN Reviewed

    Suihkonen, S.; Nykaenen, H.; Tanikawa, T.; Yamaguchi, M.; Honda, Y.; Amano, H.

    Physica Status Solidi A   Vol. 210 ( 2 ) page: 383-385   2013.2

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    DOI: 10.1002/pssa.201228457

  368. Development of High-Density Nitrogen Radical Source for Low Mosaicity and High Rate Growth of InGaN Films in Molecular Beam Epitaxy Reviewed

    Chen, S ; Kawai, Y ; Kondo, H ; Ishikawa, K ; Takeda, K ; Kano, H ; Sekine, M ; Amano, H Hori, M

    Japanese Journal of Applied Physics   Vol. 52 ( 2 ) page: 021001-021006   2013.2

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    A high-density radical source (HDRS) was developed by optimizing the antenna structure and introducing an external magnetic field to plasma. Nitrogen radical generation by the HDRS at a density of 2.3 ×1012 atoms cm-3, which was one order higher than that for the conventional radical source (CRS), was achieved. The HDRS- and CRS-assisted InGaN growth in molecular beam epitaxy (MBE) was carried out. For the HDRS case, a diffraction peak in the X-ray rocking curve of the grown InGaN films showed a narrower peak, which width below 600 arcsec even with a high growth rate of 1.4 µm/h for InGaN. MBE with the assistance of HDRS has a great potential in the growth of nitride films with a lower mosaicity and a higher growth rate.

    DOI: 10.7567/JJAP.52.021001

  369. Surface potential effect on excitons in AlGaN/GaN quantum well structures Reviewed

    Pozina, G.; Hemmingsson, C.; Amano, H.; Monemar, B.

    Applied Physics Letters   Vol. 102 ( 8 ) page: 082110/1-082110/4   2013.2

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    DOI: 10.1063/1.4793568

  370. Individual roles of atoms and ions during hydrogen plasma passivation of surface defects on GaN created by plasma etching Reviewed

    Chen, Shang; Ishikawa, Kenji; Lu, Yi; Kometani, Ryosuke; Kondo, Hiroki; Tokuda, Yutaka; Egawa, Takashi; Amano, Hiiroshi; Sekine, Amano; Hori, Masaru

    Japanese Journal of Applied Physics   Vol. 51 ( 11 ) page: 111002/1-11102/5   2012.11

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    In the recovery of photoluminescence intensities for band-edge emissions at around 3.47 eV in the case of gallium nitride (GaN), we have studied the individual roles of hydrogen atoms (H) and hydrogen ions (H-n(+)). Surface defects such as nitrogen vacancies created by plasma etching were passivated by H termination. By utilizing hydrogen plasmas, we clarified the recovery efficiency by optical and stoichiometrical improvements with respect to the balance between the fluxes of H and H-n(+). By deflecting H-n(+) by applying an electric field, the efficiency was improved using an identical H dosage, since the simultaneous irradiation of the energetic H-n(+) promoted the desorption of the formed passivated Ga-H bonds.

    DOI: 10.1143/JJAP.51.111002

  371. Correlation between device performance and defects in GaInN-based solar cells Reviewed

    Mori, Mikiko; Kondo, Shinichiro; Yamamoto, Shota; Nakao, Tatsuro; Fujii, Takahiro; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi

    Applied Physics Express   Vol. 5 ( 8 ) page: 082301/1-082301/3   2012.8

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    We investigated the correlation between the device performance and defects, such as V-shaped pits and threading dislocations, in GaInN-based solar cells. To realize high-performance GaInN-based solar cells with a high open-circuit voltage and fill factor, it is essential to realize a low pit density of less than 10(7) cm(-2). In this study, we were unable to observe clear evidence of any effect of the threading dislocation density in the GaN underlying layer.

    DOI: 10.1143/APEX.5.082301

  372. MOVPE growth of nonpolar a-plane GaN with low oxygen contamination and specular surface on a freestanding GaN substrate Reviewed

    Yasuhiro Isobe, Hiromichi Ikki, Tatsuyuki Sakakibara, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki,Takayuki Sugiyama, Hiroshi Amano, Mamoru Imade, Yusuke Mori

    Journal of Crystal Growth   Vol. 351 ( 1 ) page: 126-130   2012.7

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    We investigated unintentionally doped nonpolar a- and m-plane GaN layers grown by metalorganic vapor phase epitaxy under several sets of conditions on freestanding a- and m-plane GaN substrates. Oxygen contamination in a-plane GaN is greatly reduced by increasing the V/III ratio during growth. As a result, a high-resistivity GaN buffer layer for an AlGaN/GaN heterostructure field-effect transistor was realized.

  373. In-situ void formation technique using an AlN shell structure grown on GaN stripes on Si(111) and c-plane sapphire substrates Reviewed

    Mitsunari, Tadashi; Tanikawa, Tomoyuki; Honda, Yoshio; Yamaguchi, Masahito; Amano, Hiroshi

    Physca Status Solidi c   Vol. 9 ( 3-4 ) page: 480-483   2012.7

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    We proposed an in-situ void formation technique using high-temp. AlN growth on GaN stripes in order to reduce residual stress. Microcracks were obsd. during the growth of AlN; the GaN stripes then sublimated from the microcracks while keeping the AlN shell, resulting in void formation in the AlN shell structure. After GaN regrowth on this AlN shell structure, we successfully coalesced the GaN stripes to form a smooth, thick GaN layer having voids at the GaN/substrate interface. Raman spectroscopy confirmed that the residual tensile stress was decreased. The thermal stress decreased owing to the sepn. between the GaN layer and a foreign substrate.

    DOI: 10.1002/pssc.201100502

  374. Small current collapse in AlGaN/GaN HFETs on a-plane GaN self-standing substrate Reviewed

    T. Sugiyama, Y. Honda, M. Yamaguchi, H. Amano, Y. Isobe, M. Iwaya, T. Takeuchi, S. Kamiyama, I. Akasaki, M. Imade, Y. Kitaoka, Y. Mori

    Physica Status Solidi c   Vol. 9 ( 3-4 ) page: 875-878   2012.7

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    We measured drain bias stress effects and current collapse in AlGaN/ GaN heterostructure field-effect transistors (HFETs) on a-plane and c-plane GaN substrates. An a-plane AlGaN/GaN HFET (a-HFET) shows small current collapse with a threshold voltage (Vth = -1.8 V). On the other hand, a c-plane HFET (c-HFET) with the same barrier thickness (20 nm) shows a small current collapse, although Vth was neg. large (Vth = -4 V). Current collapse in a-HFET was not large compared with that in conventional c-HFET on GaN. A c-HFET on sapphire was also measured. The current collapses in HFETs on sapphire were larger than that in HFETs on a GaN substrate. The current collapses in the thin-barrier c-HFET (Vth = -1.8 V) were particularly large. Therefore, an a-plane device is promising for a small or pos. Vth with small current collapse.

    DOI: 10.1002/pssc.201100397

  375. Laser lift-off of AlN/sapphire for UV light-emitting diodes Reviewed

    Aoshima, Hiroki; Takeda, Kenichiro; Takehara, Kosuke; Ito, Shun; Mori, Mikiko; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi

    Physica Status Solidi C   Vol. 9 ( 3-4 ) page: 753-756   2012.7

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    We report on laser lift-off (LLO) of AlN/sapphire for UV light-emitting diodes (LEDs). Underfill between chip and submount is a key factor for the successful LLO of AlN/sapphire. We fabricated thin-film-flip-chip UV LEDs with a peak wavelength of 343 nm using the LLO. Moreover surface texturing was carried out on the exfoliated AlN surface. The light output power from the UV LED after the LLO and the surface texture at exfoliated surface is 1.7 times higher than that before the LLO at 20 mA.

    DOI: 10.1002/pssc.201100491

  376. Growth of InGaN nanowires on a (111)Si substrate by RF-MBE Reviewed

    Tabata, Takuya; Paek, Jihyun; Honda, Yoshio; Yamaguchi, Masahito; Amano, Hiroshi

    Physica Status Solidi c   Vol. 9 ( 3-4 ) page: 646-649   2012.7

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    We have grown InGaN nanowires (NWs) on a (111)Si substrate directly by radio-frequency plasma-assisted mol. beam epitaxy (RF-MBE), and investigated their In compositional distribution by energy dispersive x-ray spectroscopy (EDX). The In compn. line profiles of InGaN NWs measured by EDX are different at each position in the InGaN NWs, and In is most easily incorporated into the top of NWs. The In compn. at the top of the NWs depends on the growth temp. and the In flux ratio. However, the In compns. at other positions is not dependent on these factors. Thus, these results might be due to the limited diffusion of In atoms from the top of the NWs towards the NWs/Si interface.

    DOI: 10.1002/pssc.201100446

  377. Fabrication of AlInN/AlN/GaInN/GaN heterostructure field-effect transistors Reviewed

    Kazuya Ikeda, Yasuhiro Isobe, Hiromichi Ikki, Tatsuyuki Sakakibara, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki, Hiroshi Amano

    Physica Status Solidi c   Vol. 9 ( 3-4 ) page: 942-944   2012.7

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    We report on the electrical properties of AlInN/GaInN
    heterostructures fabricated with InN molar fractions of 0 to 0.6 in the GaInN layer. High-density two-dimensional electron gases are formed near the interfaces of AlInN/AlN/GaInN at InN molar fractions of 0.3 and 0.6.
    The Al0.82In0.18N/AlN/Ga0.4In0.6N/GaN heterostructure
    field-effect transistors exhibited static characteristics.
    The maximum drain-source current reached a value of
    0.26 A/mm.

    DOI: 10.1002/pssc.201100492

  378. High carrier concentration in high Al-composition AlGaN-channel HEMTs Reviewed

    Hashimoto, Shin; Akita, Katsushi; Yamamoto, Yoshiyuki; Ueno, Masaki; Nakamura, Takao; Yafune, Norimasa; Sakuno, Keiichi; Tokuda, Hirokuni; Kuzuhara, Masaaki; Takeda, Kenichiro; Iwaya, Motoaki; Amano, Hiroshi

      Vol. 9 ( 2 ) page: 373-376   2012.6

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    High Al-compn. (Al = 51%) and low Al-compn. (Al = 20%) AlGaN-channel high-electron-mobility transistors (HEMTs) on AlN layers with very high carrier concn. were demonstrated. In two types of HEMTs, 2-dimensional electron gases (2DEG) were clearly obsd. and peak carrier concn. and sheet carrier concn. were approx. 1020 cm-3 and higher than 2 × 1013 cm-2, resp. From the X-ray diffraction (XRD) measurements, it was obsd. that the AlGaN channel layers on the AlN layers were partially relaxed and the degree of relaxation decreased with increasing Al-compn. of AlGaN channel layers. Therefore the misfit dislocations in the high Al-compn. HEMTs were considered to be lower than those in the low Al-compn. HEMTs. Furthermore, it was revealed that very high Al-compn. of AlGaN barrier layers can be grown coherently on the AlGaN channel layers in consequence of the partly relaxation of the AlGaN channel layers, which of lattice consts. of a-axis were smaller than that of fully relaxed AlGaN channel layers. Therefore very high carrier concn. of 2DEG can be obtained in spite of the high Al-compn. of AlGaN channel layers. We considered that this high carrier concn. of 2DEG was necessary to demonstrate high Al-compn. AlGaN-channel HEMTs.

    DOI: 10.1002/pssc.201100289

  379. Progress and prospect of the growth of wide-band-gap group III nitrides: development of the growth method for single-crystal bulk GaN Reviewed

    Hiroshi Amano

      Vol. 81 ( 6 ) page: 455-463   2012.6

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  380. Crack-Free AlN/GaN Distributed Bragg Reflectors on AlN Templates Reviewed

    Kouta Yagi, Mitsuru Kaga, Kouji Yamashita, Kenichirou Takeda, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Hiroshi Amano, and Isamu Akasaki

    Japanese Journal of Applied Physics   Vol. 51   page: 051001   2012.5

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    We have demonstrated crack-free 30-pair-AlN/GaN distributed Bragg reflectors (DBRs) grown on AlN templates for the first time. A reasonably high reflectivity of 97.5% was obtained. X-ray diffraction measurements revealed that the AlN templates cause compressive stress in DBRs. At the same time, the AlN/GaN DBRs were found to relax to average AlGaN alloys with AlN mole fractions determined by the thickness ratio of the AlN layer to one pair of AlN and GaN in DBRs regardless of the underlying template, AlN or GaN.

    DOI: 10.1143/JJAP.51.051001

  381. Growth of GaN and AlGaN on (100) beta-Ga2O3 substrates Reviewed

    Shun Ito, Kenichiro Takeda, Kengo Nagata, Hiroki Aoshima, Kosuke Takehara, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki, Hiroshi Amano

      Vol. 9 ( 3-4 ) page: 519-522   2012.5

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    The crystalline quality of GaN and Al0.08Ga0.92N epitaxial layers on (100) β-Ga2O3 substrates was significantly improved by the facet-controlled growth method. The facets were controlled by changing the nitrogen ambient thermal annealing temperature. We demonstrated the highcrystalline-quality GaN and Al0.08Ga0.92N on β-Ga2O3 substrates, which were comparable to GaN and AlGaN on sapphire substrates using low-temperature buffer layers.
    This method is useful for the fabrication of verticaltype ultraviolet (UV) light-emitting diodes (LEDs) on β-Ga2O3 substrates.

    DOI: 10.1002/pssc.201100499

  382. Properties of nitride-based photovoltaic cells under concentrated light illumination Reviewed

    Shota Yamamoto, Mikiko Mori, Yosuke Kuwahara, Takahiro Fujii, Tatsuo Nakao, Shinichiro Kondo, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki, Hiroshi Amano

    Physica Status Solidi Rapid Research Letter   Vol. 6 ( 4 ) page: 145-147   2012.4

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    We investigated the properties of nitride-based solar cells under concentrated light illumination from 1 to 200 suns. The conversion efficiency of our solar cells increased with increasing concentration up to 200 suns. The short-circuit cur- rent density, open-circuit voltage, fill factor, and conversion efficiency were 510 mA/cm2, 1.9 V, 70%, and 3.4%, respectively, under an air mass filter of 1.5G at 200 suns and room temperature. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

    DOI: DOI: 10.1002/pssr.201206038

  383. Development of AlN/diamond heterojunction field effect transistors Reviewed

    Masataka Imura, Ryoma Hayakawa, Hirotaka Ohsato, Eiichiro Watanabe, Daiju Tsuya, Takahiro Nagata, Meiyong Liao, Yasuo Koide, Jun-ichi Yamamoto, Kazuhito Ban, Motoaki Iwaya, Hiroshi Amano

    Diamond and Related Materials   Vol. 24   page: 206-209   2012.4

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    AlN/diamond heterojunction field effect transistors with p-channel and normally-on depletion mode are developed, and the device performance is improved by reducing the contact resistances at source and drain contacts reported previously. The heterojunction structure is constructed from a c-axis-oriented AlN epilayer grown on oxygen-terminated (111) diamond substrate by metal-organic vapor phase epitaxy at temperatures as high as 1250 °C. Thermal treatment in the mixed hydrogen (H2) and ammonia atmosphere just before AlN growth improves the AlN adhesion to diamond surface. In addition, this treatment simultaneously produces a much larger surface hole-carrier density than that obtained by conventional H2-plasma treatment. X-ray photoelectron spectroscopy reveals the existence of carbon-nitrogen bonds at the diamond surface, and these may be responsible for such a large hole density. These results are promising in relation to new opportunities for developing diamond-based power electronic devices.

  384. Indium-Tin Oxide/Al eflective Electrodes for Ultraviolet Light-Emitting Diodes Reviewed

    Kosuke Takehara, Kenichiro Takeda, Shun Ito, Hiroki Aoshima, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki, and Hiroshi Amano

    Japanese Journal of Applied Physics   Vol. 51   page: 042101   2012.4

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    DOI: 10.1143/JJAP.51.042101

  385. Indium-Tin oxide/Al reflective electrodes for ultraviolet light-emitting diodes Reviewed

    Takehara, Kosuke; Takeda, Kenichiro; Ito, Shun; Aoshima, Hiroki; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi

      Vol. 51 ( 4 ) page: 042101/1-042101/4   2012.4

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    We investigated indium-tin oxide (ITO)/Al reflective electrodes for improving the light extraction efficiency of UV light-emitting diodes (LEDs). The ITO layer showed high transparency in the UV region upon optimization of the thickness and annealing temperature. As a result, the ITO/Al electrode exhibited both high reflectivity in the UV region and good contact characteristics simultaneously. Using this electrode, we succeeded in improving the light output power of a 350 nm UV-A LED.

    DOI: 10.1143/JJAP.51.042101

  386. Strain relaxation in thick (1-101) InGaN grown on GaN/Si substrate Reviewed

    Tomoyuki Tanikawa, Yoshio Honda, Masahito Yamaguchi, Hiroshi Amano, Nobuhiko Sawaki

    Physica Status Solidi b   Vol. 249   page: 468-471   2012.3

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    DOI: DOI: 10.1002/pssb.201100445

  387. Enhancement of two-dimensional electron gases in AlGaN-channel high-electron-mobility transistors with AlN barrier layers Reviewed

    Hashimoto Shin; Akita Katsushi; Yamamoto Yoshiyuki, HIroshi Amano

    Physica Status Solidi a   Vol. 209   page: 501-504   2012.3

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    DOI: DOI: 10.1002/pssa.201100379

  388. Improvement of Light Extraction Efficiency for AlGaN-Based Deep Ultraviolet Light-Emitting Diodes Reviewed

    Tetsuhiko Inazu, Shinya Fukahori, Cyril Pernot, Myung Hee Kim, Takehiko Fujita, Yosuke Nagasawa, Akira Hirano, Masamichi Ippommatsu, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Masahito Yamaguchi, Yoshio Honda, Hiroshi Amano, and Isamu Akasaki

    Japanese Journal of Applied Physics   Vol. 50   page: 122101   2011.12

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    AlGaN-based deep ultraviolet light-emitting diodes (LEDs) with aluminum reflective electrodes deposited to cover both p- and n-mesh contact electrodes have been fabricated. A 1.55-fold increase in light extraction efficiency has been demonstrated. Despite their reduced contact area, the LEDs exhibited only a slight increase in forward voltage of 0.45 V at 20 mA. Also, their 50% lifetime was estimated to be about 10,000 h at 20 mA DC at room temperature by extrapolation. Owing to the reflective electrodes, a 288 nm LED with external quantum efficiency as high as 5.4% was achieved. The light output power was 4.6 mW at 20 mA.

    DOI: 10.1143/JJAP.50.122101

  389. Dependence of Resonance Energy Transfer on Exciton Dimensionality Reviewed

    Jan Junis Rindermann, Galia Pozina, Bo Monemar, Lars Hultman, Hiroshi Amano, and Pavlos G. Lagoudakis

    Physical Review Letters   Vol. 107   page: 236805   2011.11

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    We investigate the dependence of resonance energy transfer from Wannier-Mott excitons to an organic overlayer on exciton dimensionality. We exploit the excitonic potential disorder in a single quantum well to tune the balance between localized and free excitons by scaling the Boltzmann distribution of excitons through temperature. Theoretical calculations predict the experimentally observed temperature dependence of resonance energy transfer and allow us to quantify the contribution of localized and free excitons. We show that free excitons can undergo resonance energy transfer with an order of magnitude higher rate compared to localized excitons, emphasizing the potential of hybrid optoelectronic devices utilizing resonance energy transfer as a means to overcome charge transfer related limitations.

  390. Fabrication of Nonpolar a-Plane Nitride-Based Solar Cell on r-Plane Sapphire Substrate Reviewed

    Tatsuro Nakao, Takahiro Fujii, Toru Sugiyama, Shota Yamamoto, Daisuke Iida, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki, and Hiroshi Amano

    Applied Physics Express   Vol. 4   page: 101001   2011.10

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    We fabricated and characterized a nonpolar a-plane nitride-based solar cell on an r-plane sapphire substrate. The maximum external quantum efficiency of the solar cell reached 62% at a wavelength of approximately 400 nm. The open-circuit voltage, the short-circuit current density, and the fill factor of the solar cell were 0.9 V, 4.8 mA/cm2, and 57%, respectively. A conversion efficiency of 1.6% was obtained from the solar cell under a solar simulator of air mass 1.5 G and an irradiation intensity of 155 mW/cm2 at room temperature. ©2011 The Japan Society of Applied Physics

    DOI: 10.1143/APEX.4.101001

  391. AlGaN-Based Deep Ultraviolet Light-Emitting Diodes Fabricated on Patterned Sapphire Substrates Reviewed

    Myunghee Kim, Takehiko Fujita, Shinya Fukahori, Tetsuhiko Inazu, Cyril Pernot, Yosuke Nagasawa, Akira Hirano, Masamichi Ippommatsu, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Masahito Yamaguchi, Yoshio Honda, Hiroshi Amano, and Isamu Akasaki

    Applie Physics Express   Vol. 4   page: 092102   2011.9

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    DOI: 10.1143/APEX.4.092102

  392. AlGaN/GaN Heterostructure Field-Effect Transistors on Fe-Doped GaN Substrates with High Breakdown Voltage Reviewed

    Yoshinori Oshimura, Takayuki Sugiyama, Kenichiro Takeda, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki and Hiroshi Amano

    Japanese Journal of Applied Physics   Vol. 50   page: 084102   2011.8

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    lGaN/GaN heterostructure field-effect transistors (HFETs) were fabricated by metalorganic vapor phase epitaxy (MOPVE) on c-plane Fe-doped GaN (GaN:Fe) substrates with different growth conditions of GaN buffer layers. The GaN buffer layers were grown at a V/III ratio of 272 at 300 Torr to realize highly resistive GaN buffer layers with automatic carbon doping. HFETs with carbon-doped GaN buffer layers showed the best characteristics among all the samples in this study. The carbon concentration was 5×1016 cm-3. In the sample with a gate-drain length of 50 µm, the off-state breakdown voltage was 2 kV or higher and the on-resistance was 18.5 mΩ·cm2. We found that the carbon-doped GaN buffer layers are necessary for high breakdown voltages even using semi-insulating GaN:Fe substrates.

  393. Luminescence related to high density of Mg-induced stacking faults in homoepitaxially grown GaN Reviewed

    S. Khromov, C. G. Hemmingsson, H. Amano, B. Monemar, L. Hultman, and G. Pozina

    Pysical Review   Vol. B84   page: 075324   2011.8

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    DOI: 10.1103/PhysRevB.84.075324

  394. Reduction in threshold current density of 355 nm UV laser diodes Reviewed

    Nagata, Kengo; Takeda, Kenichiro; Nonaka, Kentaro; Ichikawa, Tomoki; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi; Yoshida, Harumasa; et al

    Physica Status Solidi C   Vol. 8 ( 5 ) page: 1564-1568   2011.8

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    We have investigated the characteristics of 355 nm UV laser diodes. Two laser diode structures were prepd. on a grooved AlGaN template as well as on a flat AlGaN template. The threading dislocation densities on the grooved and flat AlGaN were 2.5 × 108 cm-2 and 6.5 × 109 cm-2, resp. The threshold c.d. of the laser diode on the grooved AlGaN was 6 kA/cm2, while no lasing was obsd. from the laser diode on the flat AlGaN. We also estd. the internal quantum efficiency as well as the injection efficiency in the UV laser diode structures by considering internal quantum efficiency of both optical and elec. excitation. At a carrier d. of 1.2 × 1019 cm-3, the internal quantum efficiency of the laser diode structure on the grooved AlGaN was about 50%. This is twice that of the laser diode on the flat AlGaN. At the same time, the internal quantum efficiency estd. from the optical excitation also reached about 50%, even at a carrier d. of 3 × 1018 cm-3. This implies that the injection efficiency in our UV laser diode structure was only 25%. Improving the injection efficiency should be effective for significantly reducing the threshold c.d.

  395. Low leakage current in AlGaN/GaN HFETs with preflow of Mg source before growth of u-GaN buffer layer Reviewed

    Oshimura, Yoshinori; Sugiyama, Takayuki; Takeda, Kenichiro; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi

    Physica Status Solidi A   Vol. 208 ( 7 ) page: 1607-1610   2011.7

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    AlGaN/GaN heterostructure field-effect transistors were grown by metalorg. vapor phase epitaxy on Fe-doped GaN substrates with a preflow of the Mg source. We realized a low drain leakage current, 1.05 μA/mm, at VDS = 20 V and VGS = -5 V with LGD = 3 μm. This leakage current was one order of magnitude lower than that obtained without a preflow of the Mg source. The breakdown voltage was over 250 V with LGD = 10 μm. The on resistance was estd. to be 3.6 mΩ cm2. No significant redistribution or memory effect of Mg was obsd. by secondary ion mass spectroscopy measurement.

  396. Optical properties of (1-101) InGaN/GaN MQW stripe laser structure on Si substrate Reviewed

    Murase, Tasuku; Tanikawa, Tomoyuki; Honda, Yoshio; Yamaguchi, Masahito; Amano, Hiroshi

    Physica Status Solidi C   Vol. 8 ( 7-8 ) page: 2160-2162   2011.7

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    A smooth laser structure on (1-101) GaN microstripes was successfully fabricated on a patterned (100) 8°-off Si substrate. The sample has a high internal quantum efficiency (IQE) compared with blue LEDs on a sapphire substrate. The high-d. excitation PL spectrum obsd. from the cross section of the sample shows marked narrowing, and the integral PL intensity also shows a steep increase. These results indicate the onset of stimulated emission from an InGaN-based multi quantum well (MQW) active layer on (1-101) GaN (100) Si. To the best of our knowledge, this is the first report of the observation of a stimulated emission from a (1-101) MQW on a Si substrate. We succeeded in fabricating and verifying the high-quality laser structure on semipolar (1-101) GaN on a Si substrate.

  397. Optimization of initial MOVPE growth of non-polar m- and a-plane GAN on Na flux grown LPE-GaN substrates Reviewed

    Isobe, Yasuhiro; Iida, Daisuke; Sakakibara, Tatsuyuki; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi; Imade, Mamoru; Kitaoka, Yasuo; et al

    Physica Status Solidi C   Vol. 8 ( 7-8 ) page: 2095-2097   2011.7

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    We optimized the initial GaN growths of nonpolar m- and a-plane GaN grown on liq. phase epitaxy (LPE-) GaN substrates. Such nonpolar LPE-GaN substrates were produced by cutting slices from c-plane LPE-GaN bulk single crystals grown by the Na-flux method. We investigated the qualities of epitaxially grown GaN layers on the LPE-GaN substrates, with different polishing methods, which are chem. mech. polishing and plasma dry etch polishing. We found that the cryst. quality of epitaxial GaN on m-plane GaN is very sensitive to the surface polishing even the minute unevenness in GaN substrate. Our expts. also indicated that a low initial growth rate was necessary to obtain high-cryst.-quality epitaxial m-plane GaN. In contrast, high-cryst.-quality a-plane GaN was obtained even with a high initial growth rate, indicating that the cryst. quality of a-plane GaN is not sensitive to surface roughness.

  398. Selective MOVPE growth of InGaN/GaN MQW on microfacet GaN stripes Reviewed

    Tanikawa, Tomoyuki; Murase, Tasuku; Honda, Yoshio; Yamaguchi, Masahito; Amano, Hiroshi

    Physica Status Solidi C   Vol. 8 ( 7-8 ) page: 2038-2040   2011.7

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    We demonstrated the effects of growth conditions such as growth pressure and growth temp. during the selective growth of InGaN/GaN multiple quantum wells (MQWs) on semipolar GaN microstripes on Si substrates. Grown layers exhibited the ridge growth, which indicates the thickness fluctuation, owing to the source supply from the apexes of the GaN microstructure. Ridge growth was suppressed by increasing growth pressure and decreasing growth temp. Cathode luminescence (CL) anal. showed uniform luminescence. As a result, high pressure and low temp. are suitable for obtaining uniform heterostructures in the selective growth of InGaN/GaN MQWs on GaN microstripes.

  399. Transparent electrode for UV light-emitting-diodes Reviewed

    Takehara, Kosuke; Takeda, Kenichiro; Nagata, Kengo; Sakurai, Hisashi; Ito, Shun; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi

    Physica Status Solidi C   Vol. 8 ( 7-8 ) page: 2375-2377   2011.7

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    We have investigated the transparent electrodes using indium tin oxide (ITO) for UV light-emitting diodes (LEDs). The carrier concn. of ITO was increased from 1.1 × 1018 to 1.5 × 1021 cm-3 after annealing under N2 ambient at 600 °C. The fundamental absorption edge was also shifted to a shorter wavelength owing to the increase in carrier concn., through the so-called the Burstein-Moss effect. The annealed ITO forms an ohmic contact with p-GaN with a specific contact resistance of 1.2 × 10-3 Ωcm2. The light output power of a 350 nm LED with the annealed ITO contact is 1.2 times higher than that with a conventional Ni/Au contact.

  400. Injection efficiency in AlGaN-based UV laser diodes Reviewed

    Nagata, Kengo; Takeda, Kenichiro; Oshimura, Yoshinori; Takehara, Kosuke; Aoshima, Hiroki; Ito, Shun; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; et al

    Physica Status Solidi C   Vol. 8 ( 7-8 ) page: 2384-2386   2011.7

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    We evaluated AlGaN-based 355 nm UV laser diodes prepd. under two different Mg activation conditions. The annealing processes for Mg activation in p-layers were carried out under N2 or O2 ambient to investigate the effect of the ambient gas on the laser characteristics. The threshold current densities and operating voltages of the UV laser diodes were improved by annealing under O2 compared with those under N2. We then estd. the injection efficiencies of the laser diode structures by considering the internal quantum efficiencies of optical excitation and elec. excitation. The internal quantum efficiency of the elec. excited spontaneous emission from the laser structure annealed under O2 reached 50% at a carrier d. of 7.0 × 1018 cm-3, while the structure annealed under N2 required a 1.8-fold higher carrier d. of 1.2 × 1019 cm-3 to reach the same internal quantum efficiency. In addn., the internal quantum efficiency estd. from optical excitation reached 50% even at a carrier d. of 3.0 × 1018 cm-3. This implies that the injection efficiencies in the UV laser diode structures annealed under N2 and O2 were 25% and 45%, resp. Mg activation by O2 annealing is effective for increasing the injection efficiency.

  401. Achieving high-growth-rate in GaN homoepitaxy using high-density nitrogen radical source Reviewed

    Kawai, Yohjiro; Chen, Shang; Honda, Yoshio; Yamaguchi, Masahito; Amano, Hiroshi; Kondo, Hiroki; Hirmatsu, Mineo; Kano, Hiroyuki; Yamakawa, Koji; Den, Shoji; et al

    Physica Status Solidi C   Vol. 8 ( 7-8 ) page: 2089-2091   2011.7

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    The key issue in GaN growth by radio-frequency plasma-assisted mol. beam epitaxy is the low growth rate compared with that obtained using an ammonia source. To reduce the processing time and to improve the cryst. quality of the epilayer, a high-d. radical source (HDRS) with high stability has been developed. The growth rate of the GaN epilayer was improved using the HDRS rather than a conventional radical source. During the growth, a sharp streak pattern obtained by RHEED was maintained. An atomically smooth surface was confirmed by at. force microscopy observation.

  402. AlGaN/GaInN/GaN heterostructure field-effect transistor Reviewed

    Ikki, Hiromichi; Isobe, Yasuhiro; Iida, Daisuke; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi; Bandoh, Akira; Udagawa, Takashi

    Physica Status Solidi A   Vol. 208 ( 7 ) page: 1614-1616   2011.7

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    We report on the elec. properties of AlGaN/GaInN heterostructures fabricated with various InN molar fractions from 0 to 0.60 in GaInN on a GaN template. The sheet carrier d. of the AlGaN/GaInN heterostructure monotonically increased with increasing InN molar fraction in GaInN, reaching 5.0 × 1013 cm-2 at an InN molar fraction of 0.60. The Al0.30Ga0.70N/Ga0.40In0.60N heterostructure exhibited static field-effect transistor (FET) characteristics.

  403. Development of high efficiency 255-355 nm AlGaN-based light-emitting diodes Reviewed

    Pernot, Cyril; Fukahori, Shinya; Inazu, Tetsuhiko; Fujita, Takehiko; Kim, Myunghee; Nagasawa, Yosuke; Hirano, Akira; Ippommatsu, Masamichi; Iwaya, Motoaki; Kamiyama, Satoshi, Amano Hiroshi; et al

    Physica Status Solidi A:   Vol. 208 ( 7 ) page: 1594-1596   2011.7

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    We report on the fabrication and characterization of high efficiency UV light emitting diodes (LEDs) with emission wavelength ranging from 255 to 355 nm. Epi-layers of UV LEDs were grown on AlGaN templates with sapphire substrates. Flip-chip configuration without removing sapphire is used for characterization of the UV LEDs. External quantum efficiencies (EQEs) over 3% were obtained for all the investigated wavelengths with max. value reaching 5.1% for 280 nm LED. Under RT DC operation at a current of 500 mA, output powers of 38, 77, and 64 mW were measured for 257, 280, and 354 nm, resp. By using enhanced light extn. technologies, such as, moth-eye structure on the back side of the sapphire substrate, we expect to improve these values by up to 50%.

  404. Drain bias stress and memory effects in AlGaN/GaN heterostructure field-effect transistors with p-GaN gate Reviewed

    Sugiyama, Takayuki; Honda, Yoshio; Yamaguchi, Masahito; Amano, Hiroshi; Oshimura, Yoshinori; Iida, Daisuke; Iwaya, Motoaki; Akasaki, Isamu

    Physica Status Solidi C   Vol. 8 ( 7-8 ) page: 2424-2426   2011.7

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    We measured the drain bias stress effects in normally off mode AlGaN/GaN (JHFETs) with a p-GaN gate, whose AlGaN barrier was exposed to air by dry etching. A large current collapse and a memory effect decreased the drain current (IDS). IDS of an unpassivated sample became the off leakage level of normally off mode JHFETs at a drain stress bias of 15 V. On the other hand, IDS in SiN-passivated JHFETs decreased at a slow rate upon applying drain stress bias. The decrease in IDS in SiN-passivated JHFETs was almost the same as that in asgrown HFETs. These drain stress and memory effects were perfectly deletable by light exposure, and were rewritable similarly in an EPROM.

  405. GaInN-based solar cells using GaInN/GaInN superlattices Reviewed

    Fujii, Takahiro; Kuwahara, Yousuke; Iida, Daisuke; Fujiyama, Yasuhara; Morita, Yoshiki; Sugiyama, Toru; Isobe, Yasuhiro; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; et al

    Physica Status Solidi C   Vol. 8 ( 7-8 ) page: 2463-2465   2011.7

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    We report on the fabrication of GaInN-based solar cells using GaInN/GaInN superlattices as active layers and also as underlying layers beneath the active layers. We obtained pit-free surfaces, even with a high InN molar fraction, using the superlattices. As a result, the max. external and internal quantum efficiencies reached 60%, and 88%, resp. The open-circuit voltage of the soalr cells was 1.77 V, the short-circuit c.d. was 3.08 mA/cm2, and the fill factor was 70.3%. A conversion efficiency of 2.46% was achieved at room temp. under simulared 1.5 sun × AM1.5G illumination using a solar simulator.

  406. Nonpolar a-plane AlGaN/GaN heterostructure field-effect transistors grown on freestanding GaN substrate Reviewed

    Isobe, Yasuhiro; Ikki, Hiromichi; Sakakibara, Tatsuyuki; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Sugiyama, Takayuki; Amano, Hiroshi; Imade, Mamoru; et al

    Applied Physics Express   Vol. 4 ( 6 ) page: 064102/1-064102/3   2011.6

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    We fabricated and characterized nonpolar a-plane AlGaN/GaN heterostructure field-effect transistors (HFETs) grown on an a-plane freestanding GaN substrate. By optimizing the growth conditions, the unintentionally doped oxygen concn. was much reduced in the a-plane GaN buffer layer. As a result, the low leakage current in the buffer layer was realized without doping of deep acceptors, such as Fe and C, by which an impurity-contamination-free channel layer can be successfully grown.

  407. Partial strain relaxation by stacking fault generation in InGaN multiple quantum wells grown on (1-101) semipolar GaN Reviewed

    Wu, Z. H.; Tanikawa, T.; Murase, T.; Fang, Y.-Y.; Chen, C. Q.; Honda, Y.; Yamaguchi, M.; Amano, H.; Sawaki, N.

    Applied Physics Letters   Vol. 98 ( 5 ) page: 051902/1-051902/3   2011.5

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    The authors have studied the structural properties and relaxation phenomenon of InGaN multiple quantum wells (QWs) on (1.hivin.101) semipolar GaN templates grown on patterned (001) Si substrates by selective area growth technique. Studies by TEM and x-ray diffraction reciprocal space mapping reveal that QWs emitting light at 540 nm experience significant strain relaxation along the in-plane [1.hivin.10.hivin.2] direction by the generation of an array of basal stacking faults (BSF). The generation of BSFs in 540 nm QWs could be an important factor limiting its luminescence efficiency.

  408. Internal quantum efficiency of whole-composition-range AlGaN multiquantum wells Reviewed

    Ban, Kazuhito; Yamamoto, Jun-ichi; Takeda, Kenichiro; Ide, Kimiyasu; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi

    Applied Physics Express   Vol. 4 ( 5 ) page: 052101/1-052101/3   2011.5

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    We analyze the internal quantum efficiency (IQE) of whole-compn.-range AlGaN multiquantum wells (MQWs) on AlGaN with various dislocation densities (DDs) by excitation-d.-dependent photoluminescence measurement. IQEs of deep UV/UV (DUV/UV) MQWs are strongly dependent on the DD. IQE with an excess carrier d. of 1 × 1018 cm-3 changes from 4 to 64% when the DD changes from 6 × 109 to 2 × 108 cm-2. This trend is almost the same for DUV/UV MQWs with emission wavelength ranging from 230 to 350 nm. Thus, the redn. of the DD is very important for the realization of a high-IQE DUV/UV active layer.

  409. Microstructural analysis of thick AlGaN epilayers using Mg-doped AlN underlying layer Reviewed

    Nonaka, K.; Asai, T.; Ban, K.; Yamamoto, J.; Iwaya, M.; Takeuchi, T.; Kamiyama, S.; Akasaki, I.; Amano, H.; Wu, Z. H.

    Physica Status Solidi C   Vol. 8 ( 5 ) page: 1467-1470   2011.5

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    This paper reports the microstructural anal. of 20-μm-thick Al0.5Ga0.5N with improved cryst. quality owing to the use of a Mg-doped AlN underlying layer. The threading dislocation d. in 20-μm-thick Al0.5Ga0.5N on Mg-doped AlN was 8.6 × 108 cm-2, which is about one-fifth lower than that of Al0.5Ga0.5N on an undoped AlN underlying layer. The microstructural anal. was carried out to clarify dislocation behaviors in the Al0.5Ga0.5N layer on the Mg-doped AlN underlying layer.

  410. Growth of AlGaN/GaN heterostructure on vicinal m-plane free-standing GaN substrates prepared by the Na flux method Reviewed

    Isobe, Yasuhiro; Iida, Daisuke; Sakakibara, Tatsuyuki; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi; Imade, Mamoru; Kitaoka, Yasuo; et al

    Physica Status Solidi A   Vol. 208 ( 5 ) page: 1191-1194   2011.5