Faculty Profiles - AMANO, Hiroshi

Papers - AMANO, Hiroshi

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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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

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Papers - AMANO, Hiroshi