2023/09/29 更新

写真a

タナカ アツシ
田中 敦之
TANAKA Atsushi
所属
未来材料・システム研究所 附属未来エレクトロニクス集積研究センター 未来デバイス部 特任准教授
職名
特任准教授

学位 1

  1. 博士(工学) ( 2008年3月   東京工業大学 ) 

研究キーワード 1

  1. パワーデバイス、デバイス設計、デバイスプロセス、結晶欠陥、転位、レーザ加工、GaN、SiC、半導体デバイス物理

研究分野 1

  1. ものづくり技術(機械・電気電子・化学工学) / 電子デバイス、電子機器

現在の研究課題とSDGs 1

  1. GaNパワーデバイス

経歴 6

  1. 名古屋大学   特任准教授

    2017年3月 - 現在

  2. 物質・材料研究機構   特別研究員

    2017年3月 - 2022年2月

  3. 名古屋大学   研究員

    2015年7月 - 2017年2月

  4. 産業技術総合研究所   研究員

    2010年4月 - 2015年6月

  5. 富士電機株式会社   社員

    2008年6月 - 2015年6月

  6. 東京工業大学   研究員

    2005年4月 - 2008年5月

▼全件表示

学歴 3

  1. 東京工業大学   理工学研究科   電子物理工学専攻 博士課程

    2005年4月 - 2008年3月

  2. 東京工業大学   理工学研究科   電子物理工学専攻

    2003年4月 - 2005年3月

  3. 東京工業大学   工学部   電子物理工学科

    1999年4月 - 2003年3月

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    備考: 主席

 

論文 69

  1. 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   44 巻 ( 8 ) 頁: 1328 - 1331   2023年8月

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    出版者・発行元:IEEE Electron Device Letters  

    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

    Scopus

  2. 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   44 巻 ( 7 ) 頁: 1172 - 1175   2023年7月

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    出版者・発行元:IEEE Electron Device Letters  

    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

    Scopus

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

    Park J.H., Pristovsek M., Cai W., Cheong H., Tanaka A., Furusawa Y., Han D.P., Seong T.Y., Amano H.

    Advanced Optical Materials   11 巻 ( 10 )   2023年5月

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    出版者・発行元:Advanced Optical Materials  

    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

    Scopus

  4. 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 Y., Ishikawa Y., Tanaka A., Honda Y., Nitta S., Amano H., Kurai S., Okada N., Yamada Y.

    Physica Status Solidi (A) Applications and Materials Science   220 巻 ( 16 )   2023年5月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Physica Status Solidi (A) Applications and Materials Science  

    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

    Scopus

  5. Author Correction: Laser slice thinning of GaN-on-GaN high electron mobility transistors (Scientific Reports, (2022), 12, 1, (7363), 10.1038/s41598-022-10610-4)

    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   12 巻 ( 1 )   2022年12月

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    出版者・発行元:Scientific Reports  

    The original version of this Article contained a repeated error where the symbol for micrometres “μm” was incorrectly given as millimetres “mm” in the Introduction, Experiments, Results and discussion, Figure 2 legend and the Conclusion. This error has been corrected throughout the text. The original Article has been corrected.

    DOI: 10.1038/s41598-022-12628-0

    Scopus

  6. 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   12 巻 ( 1 )   2022年12月

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    出版者・発行元:Scientific Reports  

    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

    Scopus

  7. 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   15 巻 ( 11 )   2022年11月

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    出版者・発行元:Applied Physics Express  

    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

    Scopus

  8. Evaluation of electroluminescence of AlGaN/GaN HEMT on free-standing GaN substrate

    Ma Q., Ando Y., Tanaka A., Wakejima A.

    Applied Physics Express   15 巻 ( 9 )   2022年9月

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    出版者・発行元:Applied Physics Express  

    This paper investigated electroluminescence (EL) in AlGaN/GaN high electric mobility transistors fabricated on a free-standing GaN substrate (GaN-on-GaN) with ones on a SiC substrate (GaN-on-SiC) as a reference. When a drain voltage (V ds) of the GaN-on-GaN was increased, the EL peak was kept beside the gate, indicating that the highest electric field region stayed in the vicinity of the gate. On the other hand, EL of the GaN-on-SiC shifted from the gate to the drain electrode under an increased V ds. Our results indicate that the high-electric-field tolerance of GaN-on-GaN is higher than that of GaN-on-SiC, indicating that GaN-on-GaN is more suitable for high-voltage operation.

    DOI: 10.35848/1882-0786/ac8782

    Scopus

  9. "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   15 巻 ( 4 )   2022年4月

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    出版者・発行元:Applied Physics Express  

    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.

    DOI: 10.35848/1882-0786/ac6197

    Scopus

  10. 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   120 巻 ( 12 )   2022年3月

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    出版者・発行元:Applied Physics Letters  

    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

    Scopus

  11. 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   15 巻 ( 2 )   2022年2月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Applied Physics Express  

    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

    Scopus

  12. Bias-Dependence of Electroluminescence in AlGaN/GaN High-Electron-Mobility Transistors on SiC Substrate

    Ma Q., Urano S., Tanaka A., Ando Y., Wakejima A.

    IEEE Journal of the Electron Devices Society   10 巻   頁: 297 - 300   2022年

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    出版者・発行元:IEEE Journal of the Electron Devices Society  

    This paper investigates bias-dependence of electroluminescence (EL) in an AlGaN/GaN HEMT fabricated on a SiC substrate. The HEMT exhibited a low-intensity reddish EL at the gate electrode at a drain voltage (Vds) of 30 V, which was confirmed with combination of a top-side view using a CMOS sensor camera and a back-side view using a silicon-intensified CCD. As Vds was increased to 48 V, color change from low-intensity red to high-intensity white was accompanied with shift of the location from the gate to the drain edge. The changes in the EL are attributed to a shift of the high electric field from the gate to the drain electrode and a concentration of electric field near the drain edge.

    DOI: 10.1109/JEDS.2022.3163379

    Scopus

  13. 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   11 巻 ( 1 )   2021年12月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Scientific Reports  

    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

    Scopus

    PubMed

  14. Demonstration of high thermal performance GaN-on-graphite composite bonded substrate for application in III-V nitride electronics

    Li L., Obata T., Fukui A., Takeuchi K., Suga T., Tanaka A., Wakejima A.

    Applied Physics Express   14 巻 ( 9 )   2021年9月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Applied Physics Express  

    Superior thermal performance of GaN/graphite composite (GC) bonded substrates having an ultralow thermal resistance (Rth) has been demonstrated. Thermal transition in GaN-on-GC features fast relaxation process in GaN and slow case in GC, respectively. The temperature plateau at the GaN/GC interface indicates the Rth across this interface is quite small and hence can be ignored. High-quality bonding interface and homogenous layer properties were obtained for the GaN-on-GC system. This favors the acoustic phonon transport and is bound to contribute to the outstanding thermal performance. The GaN/GC bonded substrate provides a promising candidate for thermal management applications in GaN-based electronics.

    DOI: 10.35848/1882-0786/ac15c0

    Scopus

  15. 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 and Processing   127 巻 ( 9 )   2021年9月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Applied Physics A: Materials Science and Processing  

    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

    Scopus

  16. 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   14 巻 ( 8 )   2021年8月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Applied Physics Express  

    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

    Scopus

  17. 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   60 巻 ( 7 )   2021年7月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Japanese Journal of Applied Physics  

    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

    Scopus

  18. Low temperature bonding of GaN and carbon composite via Au capping layer activated by Ar fast atom bombardment

    Takeuchi K., Tadatomo S., Tanaka A., Wakejima A.

    2021 International Conference on Electronics Packaging, ICEP 2021     頁: 43 - 44   2021年5月

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:2021 International Conference on Electronics Packaging, ICEP 2021  

    Bonding of GaN to highly thermal conductive materials such as carbon composite (CC) are expected to address the thermal management challenges in the high-power devices. The bonding interface is required to have low heat resistance. In order to avoid adapting the damage to the GaN device by high temperature bonding process, we propose the bonding of GaN to CC via thin Au layers based on the surface activation bonding technique. The Au layers deposited on GaN and CC are successfully bonded at low temperature of 150°C in air after the surface treatment using Ar ion beam irradiation.

    DOI: 10.23919/ICEP51988.2021.9451955

    Scopus

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

    Kumabe T., Ando Y., Watanabe H., Deki M., Tanaka A., Nitta S., Honda Y., Amano H.

    Japanese Journal of Applied Physics   60 巻 ( SB )   2021年5月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Japanese Journal of Applied Physics  

    Inductively coupled plasma–reactive ion etching (ICP–RIE)-induced damage in heavily Mg-doped p-type GaN ([Mg] = 2 × 1019 cm−3) was investigated by low-temperature photoluminescence (PL) and depth-resolved cathodoluminescence (CL) spectroscopy. From PL measurements, we found broad yellow luminescence (YL) with a maximum at around 2.2–2.3 eV, whose origin was considered to be isolated nitrogen vacancies (VN), only in etched samples. The depth-resolved CL spectroscopy revealed that the etching-induced YL was distributed up to the electron-beam penetration depth of around 200 nm at a high ICP–RIE bias power (Pbias). Low-bias-power (low-Pbias) ICP–RIE suppressed the YL and its depth distribution to levels similar to those of an unetched sample, and a current–voltage characteristic comparable to that of an unetched sample was obtained for a sample etched with Pbias of 2.5 W.

    DOI: 10.35848/1347-4065/abd538

    Scopus

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

    Kawasaki S., Ando Y., Deki M., Watanabe H., Tanaka A., Nitta S., Honda Y., Arai M., Amano H.

    Applied Physics Express   14 巻 ( 4 )   2021年3月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Applied Physics Express  

    We report the first experimental demonstration of microwave oscillation in GaN impact ionization avalanche time transit (IMPATT) diodes at the X-band. The device used in this study is a single drift diode with a p+–n simple abrupt junction and vertical mesa termination. The reverse I–V characteristic of the diode shows low leakage current, clear avalanche breakdown, and high avalanche capability, as required for IMPATT operation. Microwave testing is performed in an X-band waveguide circuit with a reduced-height waveguide resonant cavity. Oscillations are observed at 9.52 GHz at a power of ∼56 mW.

    DOI: 10.35848/1882-0786/abe3dc

    Scopus

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

    Yamada T., Ando Y., Watanabe H., Furusawa Y., Tanaka A., Deki M., Nitta S., Honda Y., Suda J., Amano H.

    Applied Physics Express   14 巻 ( 3 )   2021年3月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Applied Physics Express  

    Photo-electrochemical (PEC) etching is a promising technique for fabricating GaN microelectromechanical systems devices. In this study, we demonstrate the fabrication of GaN cantilevers by the bandgap-selective PEC etching of an InGaN superlattice sacrificial layer. By using an InGaN superlattice as a sacrifice layer, we found the PEC etching rate became higher than using a normal InGaN layer. As a result, the InGaN superlattice was completely etched and we fabricated GaN-based cantilevers whose resonance characteristics were measured. The Young’s modulus of GaN was determined from the resonance characteristics of GaN cantilevers to be the same as the highest value reported previously.

    DOI: 10.35848/1882-0786/abe657

    Scopus

  22. 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   118 巻 ( 7 )   2021年2月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Applied Physics Letters  

    The leakage current caused by the Si pileup at the regrowth interface of AlGaN/GaN high electron mobility transistors (HEMTs) is significantly suppressed by the semi-insulating Mg-doped GaN layer. Mg is unintentionally doped and can be originated from the graphite susceptor of metal organic vapor phase epitaxy. Before regrowth of the AlGaN/GaN heterostructure, the GaN template is treated with hydrochloric acid (HCl) and hydrogen peroxide/potassium hydroxide (H2O2/KOH) solution to promote the adsorption of Mg on the GaN surface. The Mg-doped GaN channel layer is highly resistive due to the passivation of hydrogen. The p-n junction formed by the weakly p-type Mg-doped GaN layer and the n-type Si pileup layer depletes the excess electrons at the regrowth interface. As a result, the off-state drain leakage current of the HEMT device can be decreased by two orders of magnitude at 40 V.

    DOI: 10.1063/5.0034584

    Scopus

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

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

    Applied Physics Letters   117 巻 ( 24 ) 頁: 242104 - 242104   2020年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AIP Publishing  

    GaN metal-insulator-semiconductor field-effect transistors (MISFETs) with Ni/Al2O3/GaN gate stack structures formed on a vicinal Ga-polar (c-plane) or nonpolar (m-plane) surface were fabricated. Current-voltage characteristics and carrier transport properties of the channels in the MISFETs with and without post-metallization annealing (PMA) were systematically investigated. GaN layers grown on freestanding substrates with vicinal surfaces led to good transistor behaviors for the m-plane as well as the c-plane. It was found that PMA improves the electron mobility in the MIS channel (mu(EFF)) for both the c- and m-planes, and that mu(EFF) for the m-plane is slightly higher than that for the c-plane both with and without PMA. Temperature dependences of mu(EFF) clarified that mu(EFF) for the m-plane is dominantly limited by phonon scattering, while both Coulomb and phonon scatterings are dominant for the c-plane. Consequently, we achieved high performance for the GaN MISFETs fabricated on the m-plane because of the reduced numbers of Coulomb scattering centers at the Al2O3/GaN interface. Published under license by AIP Publishing.

    DOI: 10.1063/5.0028516

    Web of Science

  24. Low interface state densities at Al<inf>2</inf>O<inf>3</inf>/GaN interfaces formed on vicinal polar and non-polar surfaces

    Ando Y., Nagamatsu K., Deki M., Taoka N., Tanaka A., Nitta S., Honda Y., Nakamura T., Amano H.

    Applied Physics Letters   117 巻 ( 10 )   2020年9月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Applied Physics Letters  

    Ni/Al2O3/GaN structures with vicinal GaN surfaces from the c- or m-plane were formed. Then, electrical interface properties of the structures were systematically investigated. It was found that interface state density (Dit) at the Al2O3/GaN interface for the c-plane is higher than that for the m-plane, and post-metallization annealing is quite effective to reduce Dit for both c- and m-planes. As a result, the low Dit value of ∼3 × 1010 eV-1 cm-2 was demonstrated for both planes.

    DOI: 10.1063/5.0010774

    Scopus

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

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

    Proceedings of the International Symposium on Power Semiconductor Devices and ICs   2020-September 巻   頁: 349 - 352   2020年9月

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Proceedings of the International Symposium on Power Semiconductor Devices and ICs  

    In this work, gallium nitride (GaN) nanowire (NW) Schottky barrier diodes was fabricated using well-optimized top-down approach. As-fabricated $100 \times 800$-nm-diameter NWs SBD with high current density over 1kA/cm2 at a forward bias of 2.2V, a low differential specific ON-resistance of $0.15\mathrm{m} \Omega \cdot cm^{2}$ are demonstrated. By the virtue of dielectric Reduced Surface Field (RESURF) effect, the device also delivers a breakdown voltage of 515V, leading to a competitive Baliga's Figure of merit of 1.76 GW/cm2.

    DOI: 10.1109/ISPSD46842.2020.9170101

    Scopus

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

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

    Applied Physics Letters   117 巻 ( 1 )   2020年7月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Applied Physics Letters  

    Recent experiments suggest that Mg condensation at threading dislocations induces current leakage, leading to degradation of GaN-based power devices. To investigate this, we perform first-principles total-energy electronic-structure calculations for various Mg and dislocation complexes. We find that threading screw dislocations (TSDs) indeed attract Mg impurities, and that the electronic levels in the energy gap induced by the dislocations are elevated toward the conduction band as the Mg impurity approaches the dislocation line, indicating that the Mg-TSD complex is a donor. The formation of the Mg-TSD complex is unequivocally evidenced by atom probe tomography in which Mg condensation around the [0001] screw dislocation is observed in a p-n diode. These findings provide a picture in which the Mg, being a p-type impurity in GaN, diffuses toward the TSD and then locally forms an n-type region. The appearance of this region along the TSD results in local formation of an n-n junction and leads to an increase in the reverse leakage current.

    DOI: 10.1063/5.0010664

    Scopus

  27. 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., Boćkowski M., Kumagai Y., Amano H.

    Journal of Crystal Growth   539 巻   2020年6月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Crystal Growth  

    Lattice bow generated by 40 µm thick HVPE homoepitaxial layers on commercial free-standing, ammonothermal and HVPE GaN wafers was studied. While a change in lattice bow was measured for all wafers, the additional bow on the ammonothermal GaN wafers was minimal. The main driving force for the observed increase in the lattice bow for HVPE wafers was related to stress in the films generated by the elongation of dislocations via climb and generation of new dislocations at the homoepitaxial interface. Lattice bow is a crucial wafer parameter as it determines the variation of the offcut across the surface. If an offcut variation of 0.1° is allowed for desired control surface morphology, composition of alloys, and uniformity of doping on this surface, the measured bow on the two HVPE GaN wafers and one ammonothermal GaN wafer limits their uniformity-diameter to ~0.5″, 1″ and >4″, respectively.

    DOI: 10.1016/j.jcrysgro.2020.125643

    Scopus

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

    Yosho D., Shintaku F., Inatomi Y., Kangawa Y., Iwata J.I., Oshiyama A., Shiraishi K., Tanaka A., Amano H.

    Physica Status Solidi - Rapid Research Letters   14 巻 ( 6 )   2020年6月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Physica Status Solidi - Rapid Research Letters  

    The oxygen incorporation kinetics of vicinal m(10−10) gallium nitride (GaN) growth during metal-organic vapor phase epitaxy is clarified using a diffusion equation-based approach that incorporates diffusion potentials obtained by large-scale density functional theory (DFT) calculations. A diffusion model based on the Burton, Cabrera and Frank (BCF) theory is proposed, and then, the oxygen concentration in the epitaxial films is calculated quantitatively. The calculation results agree with the experimental tendency that the oxygen concentration in the −c 5° off m-GaN epilayers is lower than that in the +c 5° off m-GaN epilayers. Then, the off-angle dependence of oxygen incorporation in vicinal m-GaN growth is predicted.

    DOI: 10.1002/pssr.202000142

    Scopus

  29. 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 S.F., Amano H.

    Japanese Journal of Applied Physics   59 巻 ( 5 )   2020年5月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Japanese Journal of Applied Physics  

    Magnesium (Mg) ion implantation into gallium nitride (GaN) at 1000 °C is proposed. Since ion implantation and annealing occur simultaneously in high-Temperature implantation, it is considered that Mg ions can be introduced at an appropriate position upon their implantation. GaN vertical diodes implanted with Mg ions were fabricated and current-voltage measurements were performed. As a result, clear rectifying properties were confirmed in a sample that was implanted with Mg ions at 1000 °C and annealed after implantation. However, the sample subjected to Mg ion implantation at RT and annealed after implantation showed no clear rectification. These results show that high-Temperature implantation of Mg ions at 1000 °C reduces Mg ion implantation-induced damage and simultaneously activates Mg ions upon their implantation.

    DOI: 10.35848/1347-4065/ab8b3d

    Scopus

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

    Shintaku F., Yosho D., Kangawa Y., Iwata J.I., Oshiyama A., Shiraishi K., Tanaka A., Amano H.

    Applied Physics Express   13 巻 ( 5 )   2020年5月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Applied Physics Express  

    Using density functional calculations, we clarify the oxygen incorporation mechanism in vicinal m-GaN growth by metal-organic vapor-phase epitaxy. We first identify reconstructed structures of 5° off m-GaN toward the ±c directions. Next, we explore preferable sites for oxygen substitution near step edges. We find that oxygen prefers the lower nitrogen site of the step edge on the +c 5° off m-GaN substrate compared with that on the-c 5° off m-GaN substrate. This tendency agrees with recent experimental findings that the oxygen concentration in-c 5° off m-GaN epilayers is lower than that in +c 5° off m-GaN epilayers.

    DOI: 10.35848/1882-0786/ab8723

    Scopus

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

    Tanaka A., Inotsume S., Harada S., Hanada K., Honda Y., Ujihara T., Amano H.

    Physica Status Solidi (B) Basic Research   257 巻 ( 4 )   2020年4月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Physica Status Solidi (B) Basic Research  

    Herein, a newly developed birefringence microscope is used to observe dislocations in gallium nitride (GaN) substrates. The comparison results of the observation method using this microscope with other observation methods, such as X-ray topography and Raman microscopy, confirms that dislocations in a GaN substrate can be detected with a birefringence microscope. In addition, the observation can be carried out as easily as with an optical microscope. It is also found that under certain observation conditions, the direction of the edge component of dislocations can be determined.

    DOI: 10.1002/pssb.201900553

    Scopus

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

    Takahashi M., Tanaka A., Ando Y., Watanabe H., Deki M., Kushimoto M., Nitta S., Honda Y., Shima K., Kojima K., Chichibu S.F., Chen K.J., Amano H.

    Physica Status Solidi (B) Basic Research   257 巻 ( 4 )   2020年4月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Physica Status Solidi (B) Basic Research  

    Herein, gallium nitride (GaN) samples implanted with magnesium (Mg) and fluorine (F) ions are investigated by photoluminescence (PL) measurements. In low-temperature PL measurements, the characteristic green luminescence (GL) band attributable to nitrogen vacancies (VN) is observed in Mg-ion-implanted GaN. As VN are likely to act as donors, suppressing their formation is essential to realizing p-type conductivity. The energy required for a F impurity to replace VN in GaN and eventually form F on a N site decreases when the Fermi level approaches the valence band maximum, and therefore F is employed as a subsequent implantation element to compensate for VN. The GL band peak disappears upon implanting Mg and F ions at a high temperature and adjusting the F concentration to an appropriate value. This result suggests that VN generated by Mg ion implantation can be suppressed using an element with a lower formation energy than that of VN.

    DOI: 10.1002/pssb.201900554

    Scopus

  33. 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   69 巻 ( 1 ) 頁: 1 - 10   2020年2月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Microscopy  

    Phase-shifting electron holography (PS-EH) using a transmission electron microscope (TEM) was applied to visualize layers with different concentrations of carriers activated by Si (at dopant levels of 1019, 1018, 1017 and 1016 atoms cm-3) in n-type GaN semiconductors. To precisely measure the reconstructed phase profiles in the GaN sample, three electron biprisms were used to obtain a series of high-contrast holograms without Fresnel fringes generated by a biprism filament, and a cryo-focused-ion-beam (cryo-FIB) was used to prepare a uniform TEM sample with less distortion in the wide field of view. All layers in a 350-nm-thick TEM sample were distinguished with 1.8-nm spatial resolution and 0.02-rad phase-resolution, and variations of step width in the phase profile (corresponding to depletion width) at the interfaces between the layers were also measured. Thicknesses of the active and inactive layers at each dopant level were estimated from the observed phase profile and the simulation of theoretical band structure. Ratio of active-layer thickness to total thickness of the TEM sample significantly decreased as dopant concentration decreased; thus, a thicker TEM sample is necessary to visualize lower carrier concentrations; for example, to distinguish layers with dopant concentrations of 1016 and 1015 atoms cm-3. It was estimated that sample thickness must be more than 700 nm to make it be possible to detect sub-layers by the combination of PS-EH and cryo-FIB.

    DOI: 10.1093/jmicro/dfz037

    Scopus

    PubMed

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

    Tanaka A., Nagamatsu K., Usami S., Kushimoto M., Deki M., Nitta S., Honda Y., Bockowski M., Amano H.

    AIP Advances   9 巻 ( 9 )   2019年9月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:AIP Advances  

    In this study, V-shaped dislocations in a GaN epitaxial layer on a free-standing GaN substrate were observed. Our investigation further revealed that the V-shaped dislocations were newly generated at the interface in the epilayer rather than propagated from the GaN substrate. V-shaped dislocations consist of two straight parts. The straight parts of the V-shaped dislocations were separated from each other in the m-direction and tilted toward the step-flow direction of the GaN epitaxial layer. The V-shaped dislocations are continuous single dislocations having a Burgers vector component of 1a and an intrinsic stacking fault between their straight parts.

    DOI: 10.1063/1.5114866

    Scopus

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

    Ye Z., Nitta S., Nagamatsu K., Fujimoto N., Kushimoto M., Deki M., Tanaka A., Honda Y., Pristovsek M., Amano H.

    Journal of Crystal Growth   516 巻   頁: 63 - 66   2019年6月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Crystal Growth  

    The decomposition of ammonia (NH 3 ) in nitrogen (N 2 ) ambient was studied under non-equilibrium conditions similar to those in a metal organic vapor phase epitaxy (MOVPE) reactor during the epitaxial growth of group-III nitrides. The gas phase was sampled at different positions and analyzed using a time-of-flight mass spectrometry system with a high resolution (better than 0.002 u). Our results expand earlier findings. Even at the high temperature of 1200 °C, only 26% of NH 3 decomposed in a clean metal-free reactor, whereas a higher ratio of NH 3 decomposition was realized in the presence of stainless steel. The activation energy in the clean reactor was calculated to be 0.965 ± 0.004 eV. These results demonstrate the capability of our setup and shed new light on the elucidation of the vapor phase growth mechanism of group III-nitrides by MOVPE.

    DOI: 10.1016/j.jcrysgro.2019.03.025

    Scopus

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

    Usami S., Mayama N., Toda K., Tanaka A., Deki M., Nitta S., Honda Y., Amano H.

    Applied Physics Letters   114 巻 ( 23 )   2019年6月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Applied Physics Letters  

    Mg diffusion is a common problem in GaN devices with p-n junctions. Although this impurity diffusion is reported to occur through threading dislocations (TDs), no direct evidence has yet been obtained. Therefore, we tried the direct observation of Mg diffusion by atom probe tomography (APT) analysis. The n-type drift layer of the fabricated p-n diode was exposed, and etch pits were formed on the drift layer to identify the TD position. The APT analysis around TDs was carried out by lifting out the drift layer around specific etch pits using a focused ion beam to include TDs. The relationship between the etch pit shape and the TD type was confirmed by cross-sectional scanning transmission electron microscopy observation. The APT analysis of two types of etch pits formed on the mixed dislocations was performed, and Mg diffusion was clearly observed through the mixed dislocations. In this work, we show direct evidence of Mg diffusion via mixed dislocations in GaN p-n diodes and its effect on reverse leakage current.

    DOI: 10.1063/1.5097767

    Scopus

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

    Nakano T., Chokawa K., Araidai M., Shiraishi K., Oshiyama A., Kusaba A., Kangawa Y., Tanaka A., Honda Y., Amano H.

    2019 Compound Semiconductor Week, CSW 2019 - Proceedings     2019年5月

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:2019 Compound Semiconductor Week, CSW 2019 - Proceedings  

    It is known that threading dislocations degrade the performance of GaN-based electronic devices. Electronic structure of threading dislocations in GaN is not fully understood. Accordingly, we examine the electronic structures of threading dislocations in GaN using first principles calculations based on density functional theory (DFT) and to clarify the origin of the leakage current. We have comprehensively studied the relation between threading core structures and electronic property in GaN thin films. Our calculation models of threading dislocations are the edge dislocations with Burgers vectors of 1/3 [11-20] and the screw dislocations with Burgers vectors of [0001]. We examined various core types of the threading dislocations. We found that both edge dislocations and screw dislocations do not cause the leakage currents in n-type GaN based devices because no defect level appears near the conduction band bottom.

    DOI: 10.1109/ICIPRM.2019.8819270

    Scopus

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

    Fukushima H., Usami S., Ogura M., Ando Y., Tanaka A., Deki M., Kushimoto M., Nitta S., Honda Y., Amano H.

    Applied Physics Express   12 巻 ( 2 )   2019年2月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Applied Physics Express  

    A simple structure with high breakdown voltage and a low leakage current of a vertical GaN p-n diode on a GaN free-standing substrate is demonstrated. We describe a vertical p-n diode with a simple edge termination that has a drift layer etched deeply and vertically. A device simulation revealed that the electric field was more relaxed at the device edge and applied uniformly in the entire device with increasing etching depth. We fabricated the simulated structure and succeeded in reducing the leakage current and improving the breakdown voltage. With this structure, a stable avalanche breakdown can be observed.

    DOI: 10.7567/1882-0786/aafdb9

    Scopus

  39. Anisotropic mosaicity and lattice-plane twisting of an m-plane GaN homoepitaxial layer

    Kim J., Seo O., Tanaka A., Chen J., Watanabe K., Katsuya Y., Nabatame T., Irokawa Y., Koide Y., Sakata O.

    CrystEngComm   21 巻 ( 27 ) 頁: 4036 - 4041   2019年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:CrystEngComm  

    We have observed anisotropic mosaicity of an m-plane GaN homoepitaxial layer by X-ray diffraction topography imaging over a wafer and X-ray rocking curves measured at various wafer points. Crystal domains were well aligned along the [0001] directions, but showed higher mosaicity along the [1210] direction. Images reconstructed from the full-width at half maximum showed stripe patterns along the [0001] direction. From the bending-angle images at two different azimuthal angles, we found that GaN (1010) planes were twisted along the [1210] direction, which generated anisotropic features. High resolution X-ray rocking curves revealed the multi-domain structure of GaN (1010) along the [1210] direction. The evaluated bending-angle distribution of 0.030 ± 0.013° mainly originated from the epitaxial layer twisting. We propose two possible mechanisms for this anisotropic feature and the stripe patterns correlated with epitaxial layer twisting.

    DOI: 10.1039/c9ce00463g

    Scopus

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

    Fukushima H., Usami S., Ogura M., Ando Y., Tanaka A., Deki M., Kushimoto M., Nitta S., Honda Y., Amano H.

    Japanese Journal of Applied Physics   58 巻 ( SC )   2019年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Japanese Journal of Applied Physics  

    A vertical p-n diode with a simple edge termination structure on a GaN free-standing substrate is demonstrated. The edge of this device is terminated simply by etching a drift layer deeply and vertically. A device simulation revealed that the electric field at the device edge was more relaxed and uniformly applied by etching the mesa deeper than the depletion region. The fabricated device showed low leakage current and avalanche capability, and its breakdown characteristics could be reproduced many times. By emission microscopy observation, we found that there was no leakage current at the side wall of the device and that avalanche breakdown occurred throughout the inside of the device. This indicates that the electric field crowding at the side wall of the device was completely suppressed and a uniform electric field distribution was obtained by this structure.

    DOI: 10.7567/1347-4065/ab106c

    Scopus

  41. 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 S., Tanaka A., Fukushima H., Ando Y., Deki M., Nitta S., Honda Y., Amano H.

    Japanese Journal of Applied Physics   58 巻 ( SC )   2019年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Japanese Journal of Applied Physics  

    We fabricated p-n diodes under different growth pressures on free-standing GaN substrates of the same quality and observed a noteworthy difference in the reverse leakage current. A large reverse leakage current was generated by nanopipes, which were formed from screw dislocations in the homoepitaxial layer. There were two types of screw dislocation observed in this study. The first type already existed in the substrate and the other was newly generated in the epilayer by the coalescence of edge and mixed dislocations. An increase in the growth pressure suppressed the transformation of screw dislocations into nanopipes, which led to a reduction in the reverse leakage current. To reduce the leakage current further, it is necessary to apply growth conditions that do not transform screw dislocation into nanopipes and to use a free-standing substrate without threading dislocations, that become nanopipes.

    DOI: 10.7567/1347-4065/ab1250

    Scopus

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

    Nagamatsu K., Ando Y., Ye Z., Barry O.L., Tanaka A., Deki M., Nitta S., Honda Y., Pristovsek M., Amano H.

    Japanese Journal of Applied Physics   57 巻 ( 10 )   2018年10月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Japanese Journal of Applied Physics  

    GaN vertical Schottky barrier diodes (SBDs) were grown on m-plane GaN substrates by metalorganic vapor phase epitaxy (MOVPE) using a quartz-free flow channel (FC). The use of the quartz-free FC reduced the impurity concentrations of silicon and carbon by factors of 2 and 10, respectively, compared with the concentrations obtained using a conventional reactor with a quartz FC. The oxygen concentration was found to decrease with increasing the layer thickness. We achieved the same impurity concentration for the epitaxial layers grown on m-plane GaN substrates as for those grown on c-plane GaN substrates under the same growth conditions. A high resistivity of unintentionally doped GaN was achieved by decreasing the impurity concentration. Additionally, for the further understanding of the low impurity concentration in the m-plane GaN, the n-type GaN was inserted between the m-plane GaN substrate and the drift layer. The results revealed that the c- and m-plane breakdown voltages and leakage currents have similar tendencies.

    DOI: 10.7567/JJAP.57.105501

    Scopus

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

    Tanaka A., Ando Y., Nagamatsu K., Deki M., Cheong H., Ousmane B., Kushimoto M., Nitta S., Honda Y., Amano H.

    Physica Status Solidi (A) Applications and Materials Science   215 巻 ( 9 )   2018年5月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Physica Status Solidi (A) Applications and Materials Science  

    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.

    DOI: 10.1002/pssa.201700645

    Scopus

  44. Correlation between dislocations and leakage current of p-n diodes on a free-standing GaN substrate

    Usami S., Ando Y., Tanaka A., Nagamatsu K., Deki M., Kushimoto M., Nitta S., Honda Y., Amano H., Sugawara Y., Yao Y.Z., Ishikawa Y.

    Applied Physics Letters   112 巻 ( 18 )   2018年4月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Applied Physics Letters  

    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 1c pure screw dislocations are related to the reverse leakage in vertical p-n diodes.

    DOI: 10.1063/1.5024704

    Scopus

  45. 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., Pnstovsek M., Kawai H., Yagi S., Amano H.

    Technical Digest - International Electron Devices Meeting, IEDM     頁: 30.1.1 - 30.1.4   2018年1月

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Technical Digest - International Electron Devices Meeting, IEDM  

    We will review three recent advances. Defects which cause leakage under a high-voltage reverse-biased condition were identified in GaN pin diodes grown on free-standing GaN substrates. The performances of GaN-based horizontal-heterostructure superjunction high-electron-mobility transistor and a GaN-nanorod-based vertical pn-superjunction diode were simulated. A vertical pn-superjunction was fabricated using GaN nanorod growth technology.

    DOI: 10.1109/IEDM.2017.8268477

    Scopus

  46. Theoretical study of the electronic structure of threading edge dislocations in GaN

    Nakano T., Araidai M., Shiraishi K., Tanaka A., Honda Y., Amano H.

    ECS Transactions   86 巻 ( 12 ) 頁: 41 - 49   2018年

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:ECS Transactions  

    It is very important to fabricate high-quality GaN especially used for power devices. However, threading dislocations degrade the performance of GaN-based electronic devices. It is necessary to examine the electronic behavior at threading dislocations in GaN and to clarify the origin of the leakage current. As for theoretical studies, the electronic structure of threading dislocations in GaN is not fully understood. We investigated whether threading edge dislocations contribute to the leakage current or not. To do this, we used first principles calculations based on density functional theory (DFT) to examine the electronic structure at threading edge dislocations with Burgers vectors of 1/3[11-20]. We examined four core types of atomic structure at threading edge dislocations which contains about 200 atoms. Compared with dislocation line energies of each core configurations, it was found that the 5/7-atoms ring core and 8-atoms ring core are energetically stable. Then, we analyzed the electronic densities of states of each core configurations, and it was found that all types of core configurations at threading edge dislocations do not contribute to leakage current in n-type GaN-based devices.

    DOI: 10.1149/08612.0041ecst

    Scopus

  47. Initial leakage current paths in the vertical-type GaN-on-GaN Schottky barrier diodes

    Sang L., Ren B., Sumiya M., Liao M., Koide Y., Tanaka A., Cho Y., Harada Y., Nabatame T., Sekiguchi T., Usami S., Honda Y., Amano H.

    Applied Physics Letters   111 巻 ( 12 )   2017年9月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Applied Physics Letters  

    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

    Scopus

  48. Effect of dislocations on the growth of p-type GaN and on the characteristics of p–n diodes

    Usami S., Miyagoshi R., Tanaka A., Nagamatsu K., Kushimoto M., Deki M., Nitta S., Honda Y., Amano H.

    Physica Status Solidi (A) Applications and Materials Science   214 巻 ( 8 )   2017年8月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Physica Status Solidi (A) Applications and Materials Science  

    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

    Scopus

  49. Facet dependence of leakage current and carrier concentration in m-plane GaN Schottky barrier diode fabricated with MOVPE

    Tanaka A., Barry O., Nagamatsu K., Matsushita J., Deki M., Ando Y., Kushimoto M., Nitta S., Honda Y., Amano H.

    Physica Status Solidi (A) Applications and Materials Science   214 巻 ( 8 )   2017年8月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Physica Status Solidi (A) Applications and Materials Science  

    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

    Scopus

  50. Effect of V/III ratio on the surface morphology and electrical properties of m–plane (101¯0) GaN homoepitaxial layers

    Barry O.I., Tanaka A., Nagamatsu K., Bae S.Y., Lekhal K., Matsushita J., Deki M., Nitta S., Honda Y., Amano H.

    Journal of Crystal Growth   468 巻   頁: 552 - 556   2017年6月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Crystal Growth  

    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

    Scopus

  51. Growth of Shockley type stacking faults upon forward degradation in 4H-SiC p-i-n diodes

    Tanaka A., Matsuhata H., Kawabata N., Mori D., Inoue K., Ryo M., Fujimoto T., Tawara T., Miyazato M., Miyajima M., Fukuda K., Ohtsuki A., Kato T., Tsuchida H., Yonezawa Y., Kimoto T.

    Journal of Applied Physics   119 巻 ( 9 )   2016年3月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Applied Physics  

    The growth of Shockley type stacking faults in p-i-n diodes fabricated on the C-face of 4H-SiC during forward current operation was investigated using Berg-Barrett X-ray topography and photoluminescence imaging. After forward current experiment, Shockley type stacking faults were generated from very short portions of basal plane dislocations lower than the conversion points to threading edge dislocations in the epitaxial layer. The growth behavior of Shockley type stacking faults was discussed. Growth of stacking faults in the substrates was not observed.

    DOI: 10.1063/1.4943165

    Scopus

  52. Effects of basal plane dislocation density in 4H-SiC substrate on degradation of body-diode forward voltage

    Kawabata N., Tanaka A., Tsujimura M., Ueji Y., Omote K., Yamaguchi H., Matsuhata H., Fukuda K.

    Materials Science Forum   858 巻   頁: 384 - 388   2016年

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Materials Science Forum  

    We investigated the effect of the basal plane dislocation (BPD) density in 4H-silicon carbide (SiC) substrates on the forward voltage (Vsd) degradation of body-diodes. Using reflection X-ray topography, the BPD density was automatically estimated from the substrates prior to fabrication of metal–oxide–semiconductor field-effect transistors (MOSFETs). A strong positive correlation was found between the Vsdshift, which was calculated from the difference before and after forward bias stress at 160 A/cm2for ~500 hours, and the BPD density of the substrate. We show that it is possible to predict Vsdshifts from the BPD densities of SiC substrates prior to the fabrication of MOSFETs. In addition, we examined the origin of stacking faults (SFs) as a result of the application of forward bias stress. We presume that SFs are formed by BPDs converted to threading edge dislocations at the epi/sub interface, as well as by BPDs penetrating into the epitaxial layer.

    DOI: 10.4028/www.scientific.net/MSF.858.384

    Scopus

  53. Annealing temperature dependence of dislocation extension and its effect on electrical characteristic of 4H-SiC PIN diode

    Tanaka A., Kawabata N., Tsujimura M., Furukawa Y., Hoshino T., Ueji Y., Omote K., Yamaguchi H., Matsuhata H., Fukuda K.

    Materials Science Forum   821-823 巻   頁: 315 - 318   2015年

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Materials Science Forum  

    In this study, we investigated the annealing temperature dependence of dislocation extension in an ion-implanted region of a 4H-silicon carbide (SiC) C-face epitaxial layer, revealing that a high temperature annealing led to dislocation formation. We also investigated the currentvoltage (I-V) characteristics of a 4H-SiC PIN diode with and without these extended dislocations. We demonstrated that the forward biased I-V characteristics of samples with extended interfacial dislocations have a kink at lower current regions.

    DOI: 10.4028/www.scientific.net/MSF.821-823.315

    Scopus

  54. Dynamic characteristics of large current capacity module using 16-kV ultrahigh voltage SiC flip-type n-channel IE-IGBT

    Mizushima T., Takenaka K., Fujisawa H., Kato T., Harada S., Tanaka Y., Okamoto M., Sometani M., Okamoto D., Kumagai N., Matsunaga S., Deguchi T., Arai M., Hatakeyama T., Makifuchi Y., Araoka T., Oose N., Tsutsumi T., Yoshikawa M., Tatera K., Tanaka A., Ogata S., Nakayama K., Hayashi T., Asano K., Harashima M., Sano Y., Morisaki E., Takei M., Miyajima M., Kimura H., Otsuki A., Yonezawa Y., Fukuda K., Okumura H., Kimoto T.

    Proceedings of the International Symposium on Power Semiconductor Devices and ICs     頁: 277 - 280   2014年

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Proceedings of the International Symposium on Power Semiconductor Devices and ICs  

    4H-SiC carbon face flip-type n-channel implantation and epitaxial (IE)-IGBT with an epitaxial p++ substrate was developed and its switching test was carried out. We were able to achieve an ultrahigh blocking voltage greater than 16 kV, extremely low Von (6.35 V at 20 A), and good temperature stability. The switching operation was achieved by connecting three IGBTs in parallel, with a total ICE of 60 A and VCE 5 kV. The turn-off loss and turn-on loss were about 220 mJ and 120 mJ, respectively at room temperature. They show low switching loss of ultrahigh voltage SiC IE-IGBT and the possibility of large scale module with parallel connection. © 2014 IEEE.

    DOI: 10.1109/ISPSD.2014.6856030

    Scopus

  55. High performance SiC IEMOSFET/SBD module

    S. Harada, Y. Hoshi, Y. Harada, T. Tsuji, A. Kinoshita, M. Okamoto, Y. Makifuchi, Y. Kawada, K. Imamura, M. Gotoh, T. Tawara, S. Nakamata, T. Sakai, F. Imai, N. Ohse, M. Ryo, A. Tanaka, K. Tezuka, T. Tsuyuki, S. Shimizu, N. Iwamuro, Y. Sakai, H. Kimura, K. Fukuda, H. Okumura

    Materials Science Forum   717-720 巻   頁: 1053 - 1058   2012年

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    掲載種別:研究論文(国際会議プロシーディングス)  

    SiC power module with low loss and high reliability was developed by utilizing IEMOSFET and SBD. The IEMOSFET is the SiC MOSFET with high channel mobility in which the channel region is the p-type carbon-face epitaxial layer with low acceptor concentration. Elemental technologies for the high channel mobility and the high reliability of the gate oxide have been developed to realize the excellent characteristics by the IEMOSFET. The SBD was designed so as to minimize the forward voltage drops and the reverse leakage current. For the fabrication of these SiC power devices, the mass production technologies such as gate oxidation, ion implantation and following activation annealing have been also developed. © (2012) Trans Tech Publications.

    DOI: 10.4028/www.scientific.net/MSF.717-720.1053

    Scopus

  56. Influence of the crystal orientation of substrate on low temperature synthesis of silicon nanowires from Si<inf>2</inf>H<inf>6</inf>

    Akhtar S., Tanaka A., Usami K., Tsuchiya Y., Oda S.

    Thin Solid Films   517 巻 ( 1 ) 頁: 317 - 319   2008年11月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Thin Solid Films  

    SiNW synthesis by vapor-liquid-solid (VLS) growth mechanism has been reported by many authors but a deep understanding of the key factors affecting the nanowire growth is still lacking. Here, we report a thorough investigations of the SiNW growth by employing silicon substrates with different crystal orientations and surface preparation using Au thin film as a catalyst. We observed that the activity of the Au particles strongly depends on the crystal orientation and the substrate surface preparation significantly affects the properties of SiNWs. We found that the density and growth rate of nanowires is different in a temperature dependent growth on Si(100) from Si(111). We found that the density and growth rate of nanowires is different at different crystal orientations of the substrates. We have grown nearly uniform diameter and micrometer long SiNWs by using Si2H6 as a source gas in low pressure chemical vapor deposition around eutectic temperature. The length of the SiNWs can be controlled mainly by varying the growth time. © 2008 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.tsf.2008.08.155

    Scopus

  57. Visible electroluminescence from spherical-shaped silicon nanocrystals

    Cheong H.J., Tanaka A., Hippo D., Usami K., Tsuchiya Y., Mizuta H., Oda S.

    Japanese Journal of Applied Physics   47 巻 ( 10 PART 1 ) 頁: 8137 - 8140   2008年10月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Japanese Journal of Applied Physics  

    We fabricated light emitting diodes (LEDs) using spherically shaped nanocrystalline silicon (nc-Si), which was formed through very high frequency (VHF; 144 MHz) plasma decomposition of SiH4. In addition, we successfully reduced the roughness of the surface and part of the voids separating the dots by finding the adequate annealing conditions. Red electroluminescence was also observed at 12 V with the naked eye at room temperature under forward bias condition. It is suggested that the origin of the electroluminescence (EL) from Si nanocrystals is due to recombination centers in Si nanocrystals by the comparison of EL and photoluminescence spectra. © 2008 The Japan Society of Applied Physics.

    DOI: 10.1143/JJAP.47.8137

    Scopus

  58. Synthesis of assembled nanocrystalline si dots film by the langmuir-blodgett technique

    Tanaka A., Tsuchiya Y., Usami K., Saito S.i., Arai T., Mizuta H., Oda S.

    Japanese Journal of Applied Physics   47 巻 ( 5 PART 1 ) 頁: 3731 - 3734   2008年5月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Japanese Journal of Applied Physics  

    We report on a new bottom-up technique for forming silicon nanostructures based on the assembly of nanocrystalline Si (nc-Si) dots by the Langmuir-Blodgett technique. nc-Si dots with a diameter of 10 ± 1 nm fabricated by a very high frequency (VHF) plasma process are dispersed in solvent and functionalized with an appropriate silane coupling agent. After compression at the surface of a Langmuir trough to form a well-organized two-dimensional array, nc-Si dots are transferred onto Si substrates. We have succeeded in forming a well-assembled nc-Si dot array with an area density of 7.33 × 1011 cm-2. Furthermore, we clarified what happens at the surface of a Langmuir trough based by analyzing surface pressure-area isotherms. ©2008 The Japan Society of Applied Physics.

    DOI: 10.1143/JJAP.47.3731

    Scopus

  59. Light emission from size reduced nanocrystal silicon quantum dots

    Cheong H.J., Tanaka A., Hippo D., Usami K., Tsuchiya Y., Mizuta H., Oda S.

    Optics InfoBase Conference Papers     2007年

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Optics InfoBase Conference Papers  

    We performed HF treatment to silicon quantum dots with diameter of 8nm±1nm fabricated by VHF plasma decomposition process. We observed PL wavelength shift from 750nm to 620nm for 8nm to 2.5nm diameter nc-Si dots. © 2007 Optical Society of America.

    Scopus

  60. Light emission from size reduced nanocrystal silicon quantum dots

    Cheong H.J., Tanaka A., Hippo D., Usami K., Tsuchiya Y., Mizuta H., Oda S.

    Conference on Quantum Electronics and Laser Science (QELS) - Technical Digest Series     2007年

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Conference on Quantum Electronics and Laser Science (QELS) - Technical Digest Series  

    We performed HF treatment to silicon quantum dots with diameter of 8nm±1nm fabricated by VHF plasma decomposition process. We observed PL wavelength shift from 750nm to 620nm for 8nm to 2.5nm diameter nc-Si dots. ©2007 Optical Society of America.

    DOI: 10.1109/QELS.2007.4431332

    Scopus

  61. Light emission from size reduced nanocrystal silicon quantum dots

    Cheong H.J., Tanaka A., Hippo D., Usami K., Tsuchiya Y., Mizuta H., Oda S.

    Conference on Lasers and Electro-Optics, 2007, CLEO 2007     2007年

     詳細を見る

    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Conference on Lasers and Electro-Optics, 2007, CLEO 2007  

    We performed HF treatment to silicon quantum dots with diameter of 8nm±1nm fabricated by VHF plasma decomposition process. We observed PL wavelength shift from 750nm to 620nm for 8nm to 2.5nm diameter nc-Si dots. © 2007 Optical Society of America.

    DOI: 10.1109/CLEO.2007.4453555

    Scopus

  62. Light emission from size reduced nanocrystal silicon quantum dots

    Cheong H.J., Tanaka A., Hippo D., Usami K., Tsuchiya Y., Mizuta H., Oda S.

    Optics InfoBase Conference Papers     2007年

     詳細を見る

    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Optics InfoBase Conference Papers  

    We performed HF treatment to silicon quantum dots with diameter of 8nm±1nm fabricated by VHF plasma decomposition process. We observed PL wavelength shift from 750nm to 620nm for 8nm to 2.5nm diameter nc-Si dots. © 2007 Optical Society of America.

    Scopus

  63. Light emission from size reduced nanocrystal silicon quantum dots

    Cheong H.J., Tanaka A., Hippo D., Usami K., Tsuchiya Y., Mizuta H., Oda S.

    Optics InfoBase Conference Papers     2007年

     詳細を見る

    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Optics InfoBase Conference Papers  

    We performed HF treatment to silicon quantum dots with diameter of 8nm±1nm fabricated by VHF plasma decomposition process. We observed PL wavelength shift from 750nm to 620nm for 8nm to 2.5nm diameter nc-Si dots. © 2007 Optical Society of America.

    Scopus

  64. High-density assembly of nanocrystalline silicon quantum dots

    Tanaka A., Yamahata G., Tsuchiya Y., Usami K., Mizuta H., Oda S.

    Current Applied Physics   6 巻 ( 3 ) 頁: 344 - 347   2006年6月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Current Applied Physics  

    This paper reports on a new bottom-up technique of forming silicon nanostructures based on assembly of nanocrystalline (nc) Si dots from the solution. The nc-Si dots with a diameter of 8 ± 1 nm were fabricated by using VHF plasma decomposition of pulsed SiH4 gas supply and deposited on the substrate randomly. We first studied the method of making the nc-Si dot dispersion solution by immersing the deposited wafer into various kinds of solvent with ultra sonic treatment. We found that methanol works as a suitable solvent for nc-Si dots. We then add a drop of the nc-Si dot solution onto other substrates and evaporated it. During the evaporation the nc-Si dots were assembled in the solution via the lateral capillary meniscus force which works as an attractive force between the dots. Use of SiO2 substrate with good surface wettability with the solution was found vital to have the maximum meniscus force and to have two-dimensional assembly of the dots. The evaporation speed was carefully controlled via temperature and evaporation pressure to achieve high dot density assembly. In addition, we examined the assembly of the nc-Si dots on the silicon-on-insulator substrates with various kinds of nanoscale patterning and succeeded in making the nc-Si dots cluster bridging between the nanoelectrodes with a gap of as small as 20 nm. © 2005 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.cap.2005.11.015

    Scopus

  65. Nanocrystalline silicon quantum dot devices

    Oda S., Huang S.Y., Salem M.A., Hippo D., Tanaka A., Tsuchiya Y., Mizuta H.

    ICSICT-2006: 2006 8th International Conference on Solid-State and Integrated Circuit Technology, Proceedings     頁: 1045 - 1048   2006年

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:ICSICT-2006: 2006 8th International Conference on Solid-State and Integrated Circuit Technology, Proceedings  

    Electron transport and photonic properties of silicon nanocrystals prepared by plasma decomposition of silane are described with particular emphasis on silicon nanocrystals memory, microscopic charge measurement by KFM, NEMS devices, and silicon photonic devices. © 2006 IEEE.

    DOI: 10.1109/ICSICT.2006.306657

    Scopus

  66. Visible electroluminescence from size-controlled silicon quantum dots

    Cheong H.J., Hippo D., Tanaka A., Usami K., Tsuchiya Y., Mizuta H., Oda S.

    Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, CLEO/QELS 2006     2006年

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, CLEO/QELS 2006  

    We studied visible EL from size-controlled silicon quantum dots with diameter of 8nm±1nm fabricated by VHF plasma decomposition process. We observed EL from nc-Si quantum dots with applied voltage above 12V. © 2006 Optical Society of America.

    DOI: 10.1109/CLEO.2006.4628248

    Scopus

  67. A new design of nanocrystalline silicon optical devices based on 3-dimensional photonic crystal structures

    Hippo D., Chong H.J., Kawata Y., Tanaka A., Tsuchiya Y., Mizuta H., Oda S., Urakawa K., Koshida N.

    2005 IEEE International Conference on Group IV Photonics   2005 巻   頁: 114 - 116   2005年

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:2005 IEEE International Conference on Group IV Photonics  

    We propose a new design of nanocrystalline silicon optical devices which are based on control of electromagnetic fields, electronic states, as well as the phonon dispersion of size-controlled silicon quantum dots.

    DOI: 10.1109/GROUP4.2005.1516422

    Scopus

  68. Assembly of nanocrystalline silicon quantum dots based on a colloidal solution method

    Tanaka A., Yamahata G., Tsuchiya Y., Usami K., Mizuta H., Oda S.

    2005 5th IEEE Conference on Nanotechnology   2 巻   頁: 795 - 798   2005年

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:2005 5th IEEE Conference on Nanotechnology  

    In this paper we propose and develop a new bottom-up approach to the formation of silicon nanostructures based on assembly of nanocrystalline (ne) Si dots from the colloidal solution. The nc-Si dots with a diameter of 8±1nm were fabricated by using VHF plasma decomposition of pulsed SiH4 gas supply and deposited on the substrate randomly. For preparing the nc-Si dot colloidal solution, we first examined various kinds of solvent. The substrates on which the nc-Si dots deposited were immersed into the solvents, and ultra sonic treatment was applied for a few tens seconds. It was found that methanol works as a suitable solvent for nc-Si dots. The nc-Si dot solution was then condensed by evaporating the solvent a fraction. We dropped the nc-Si dot solution onto other substrates and evaporated it completely. We observed that the nc-Si dots were assembled in the solution via the lateral capillary meniscus force which works as an attractive force between the dots. Use of SiO2 substrate with good surface wettability with the solution was found vital to have the maximum meniscus force and to have two-dimensional assembly of the dots. The evaporation speed was carefully controlled via temperature and evaporation pressure to achieve high dot density assembly. In addition, we examined the assembly of the nc-Si dots on the silicon-on-insulator substrates with various kinds of nanoscale patterning and succeeded in making the nc-Si dots cluster bridging between the nano-electrodes with a gap of as small as 20 nm. ©2005 IEEE.

    DOI: 10.1109/NANO.2005.1500651

    Scopus

  69. Formation of an ordered array of nanocrystalline Si dots by using a solution droplet evaporation method

    Tsuchiya Y., Iwasa T., Tanaka A., Usami K.I., Mizuta H., Oda S.

    Materials Research Society Symposium Proceedings   818 巻   頁: 347 - 352   2004年

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Materials Research Society Symposium Proceedings  

    This paper reports on a new bottom-up technique of forming silicon nanostructures based on natural aggregation of nanocrystalline (nc) -Si dots in the solution. We first study how the nc-Si dots deposited on the Si substrate get mobile in the solution by simply dipping the substrate with the nc-Si dots on into various solutions. We then demonstrate a solution droplet evaporation method that utilizes aggregation of the dots when we evaporate a solution droplet applied onto the nc-Si dots randomly deposited on the Si substrate. It is shown that the nc-Si dots are assembled well in a droplet of the hydrofluoric acid solution, resulting in various regular patterns on the substrate.

    DOI: 10.1557/proc-818-m11.51.1

    Scopus

▼全件表示

書籍等出版物 2

  1. シリコンと化合粒半導体の超精密・微細加工プロセス技術

    ( 担当: 共著 ,  範囲: 第7章 レーザスライスによるGaN基板の切り出し加工)

    シーエムシー出版  2023年10月 

  2. 次世代パワーエレクトロニクスの課題と評価技術

    ( 担当: 共著 ,  範囲: 第1章第2節 GaNのパワーデバイスの動向と技術課題)

    S&T出版  2022年7月 

MISC 1

  1. Impact of SiN passivation film stress on electroluminescence characteristics of AlGaN/GaN high-electron-mobility transistors

    Ma Q., Urano S., Ando Y., Tanaka A., Wakejima A.  

    Applied Physics Express14 巻 ( 9 )   2021年9月

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    掲載種別:速報,短報,研究ノート等(学術雑誌)   出版者・発行元:Applied Physics Express  

    This letter reports an impact of SiN film stress on electroluminescence (EL) of AlGaN/GaN HEMTs. The EL color of HEMTs turned from high-intensity white to low-intensity red, as the SiN film stress was increased from -24.2 (compressive) to +11.5 MPa (tensile). The weak reddish EL from the HEMT with a film stress of +11.5 MPa turned bright whitish when a drain-to-source voltage (V ds) was increased. A transient I d response after biasing stress revealed that severe current collapse emerged in the HEMT with a film stress of -24.2 MPa. In addition, the current collapse in HEMTs increased with the increased V ds.

    DOI: 10.35848/1882-0786/ac1f40

    Scopus

共同研究・競争的資金等の研究課題 1

  1. 5Gの普及・展開のための基盤技術に関する研究開発

    2018年4月 - 2020年3月

    電波資源拡大のための研究開発 

    田中敦之

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

    配分額:178500000円

    GaN基板のレーザスライスに関する研究

科研費 3

  1. HVPE法によるGaNのpn接合周期構造の高速成長とSJダイオードの作製

    研究課題/研究課題番号:22K18808  2022年6月 - 2024年3月

    科学研究費助成事業  挑戦的研究(萌芽)

    本田 善央, 田中 敦之, 新田 州吾

      詳細を見る

    担当区分:研究分担者 

    これまで実現していないGaNを用いたSJダイオードの作製を目指す。我々は、高速成長可能なHVPE法におけるp型伝導の実現に成功したことから、pn接合の厚膜化を可能とした。本手法を利用して、SJ構造のpn接合周期構造の成長を試みる。p型不純物に用いるMgの成長中での拡散による深さ方向への不純物濃度の不均一の抑制、厚膜化に伴う表面モフォロジーの悪化およびデバイスプロセスの確立を図る。SJダイオードを作製し特性を得ることを目的とし、そのための基礎的な成長~プロセス技術を構築する。

  2. GaNパワーデバイス実用化に向けたデバイス内部の電界強度分布直接観察に関する研究

    研究課題/研究課題番号:20K04578  2020年4月 - 2023年3月

    科学研究費助成事業  基盤研究(C)

    田中 敦之

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    担当区分:研究代表者 

    配分額:4420000円 ( 直接経費:3400000円 、 間接経費:1020000円 )

    今回の手法は半導体であるGaN中に光を照射して電荷を発生させ、この電荷がGaN中を移動することを電流として検出します。この電流はGaN内部の電界強度分布の影響を受けるので電流から電界強度分布の情報が得られます。今回特に新しいのはこの電荷の生成位置を三次元的に制御した状態で行う技術を用いることです。これによりGaN中の電界強度分布を三次元的に観察することが可能です。新しい手法であるので、研究開始後はまず、電流値から電界に直すためのデータ取得を行い、電流値をみれば電界強度に校正できるようにします。その後、これらの手法を用いてGaNの物性値評価等を行います。
    今年度は交付申請書に記載した「問い」のうち、実デバイスとシミュレーションの耐圧の乖離については、多光子PL-OBICを用いた衝突電離係数の広範囲精密測定により、GaNの衝突電離係数がこれまでは不正確なもので見積れられていたためであることを明らかにし、今回の手法及び広範囲において精密に計測されたGaNの衝突電離係数について論文化を進めている。漏れ電流に関しては多数の転位を含んだデバイスでは転位一つの影響に中々迫れなかったため10^4 cm^-2乗台の転位密度の基板を用いて、転位が一個入るか入らないかのデバイスを用いて転位一つ一つの影響を丹念に調べている。大きく漏れる転位の発生は少なくまだあたれていないが、その他の転位が存在する場合については調べが進んでおり、無転位のデバイスと比べると、アバランシェ降伏時の電流の立ち上がりが多少緩やかになる程度の違いしかないことを突き止めており、その原因を追究中である。また多光子PL-OBICに関しては、伝導度変調が起きていないGaN-pnダイオードの順方向高注入状態において、多光子PLを用いてキャリアを補いその際の反応をドリフト層位置ごとに見ることによって、キャリア濃度分布を疑似的に観察できることを見出し研究を進めている。
    年次計画表作製時の筋書き通りには研究は進んでいないが、多光子PL-OBICを利用して様々な結果が出てきている点、転位のデバイスへの影響に関しても新しいことを発見できている点を考慮して順調に進展しているとした。
    これまでの研究経緯から考えると、転位周辺での伝導形態の解明に多光子PL-OBICが強力なツールになっているかは怪しいところである。しかし、その研究過程で明らかになってきた転位がデバイスに与える影響の研究、デバイス内部の電界やキャリア状態を探る手法としての多光子PL-OBIC活用の研究についてはそれぞれ必ずしも連携させる必要はないものとして進める。

  3. GaNパワーデバイスの実用化に向けた、転位のデバイスに与える影響及び原理の解明

    研究課題/研究課題番号:17K17808  2017年4月 - 2020年3月

    科学研究費助成事業  若手研究(B)

    田中 敦之

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    担当区分:研究代表者 

    配分額:4290000円 ( 直接経費:3300000円 、 間接経費:990000円 )

    GaNパワーデバイスにおける、GaN結晶中の転位がデバイスにどのような影響を与えるかについての研究を行った。その成果として、1cの螺旋転位部分がpinダイオードに存在して居ると逆方向電圧印加時にリークを引き起こしていることを明らかにした。また、上記の成果を得る過程で、複屈折顕微鏡像によるGaN中転位のバーガースベクトル判別、繰り返しアバランシェ降伏可能なpinダイオードの作製方法、GaN中基底面転位の多光子励起キャリアによるREDGの発生確認等の成果も得ることが出来た。
    今後、持続可能な社会を実現していく上で、電力エネルギーに関しては低消費電力化という取り組みが重要になってくる。この低消費電力化においてGaNパワーデバイスは非常に重要な役割を担う事が期待されている。その役割を担うためにはGaN結晶についての深い理解が必要であり、本研究成果はGaN結晶をパワーデバイスに用いる際に知っておくべきことを学術的に明らかにしたものである。

産業財産権 27

  1. 窒化物半導体装置の製造方法及び窒化物半導体基板

    本田善央、天野浩、田中敦之、伊藤佑太

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    出願番号:特許出願2021-174661  出願日:2021年10月

  2. 基板製造方法

    田中敦之、瀬奈ハディ

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    出願番号:特許出願2021-032709  出願日:2021年3月

  3. レーザ加工方法、半導体部材製造方法、及び、レーザ加工装置

    田中敦之、笹岡千秋、天野浩、河口大祐、油井俊樹、和仁陽太郎、杉浦隆二

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    出願番号:特許出願2020-015056  出願日:2020年1月

  4. レーザ加工方法、半導体部材製造方法、及び、レーザ加工装置

    田中敦之、笹岡千秋、天野浩、河口大祐、油井俊樹、和仁陽太郎

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    出願番号:特許出願2020-015060  出願日:2020年1月

  5. レーザ加工方法、半導体部材製造方法及びレーザ加工装置

    田中敦之、笹岡千秋、天野浩、河口大祐、和仁陽太郎、伊ケ崎泰則

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    出願番号:特許出願108146614  出願日:2019年12月

    出願国:外国  

  6. レーザ加工方法、半導体部材製造方法及びレーザ加工装置

    田中敦之、笹岡千秋、天野浩、河口大祐、和仁陽太郎、伊ケ崎泰則

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    出願番号:特許出願108146615  出願日:2019年12月

    出願国:外国  

  7. レーザ加工方法、半導体部材製造方法、及び半導体対象物

    田中敦之、笹岡千秋、天野浩、河口大祐、和仁陽太郎、伊ケ崎泰則

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    出願番号:特許出願108146331  出願日:2019年12月

    出願国:外国  

  8. レーザ加工方法、半導体部材製造方法、及び半導体対象物

    田中敦之、笹岡千秋、天野浩、河口大祐、和仁陽太郎、伊ケ崎泰則

     詳細を見る

    出願番号:特許出願PCT/JP2019/046656  出願日:2019年11月

    出願国:外国  

  9. レーザ加工方法、半導体部材製造方法及びレーザ加工装置

    田中敦之、笹岡千秋、天野浩、河口大祐、和仁陽太郎、伊ケ崎泰則

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    出願番号:特許出願2018-239883  出願日:2018年12月

  10. 縦型高耐圧半導体装置及びその製造方法

    田中敦之、岩室憲幸、原田信介

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    出願番号:特許出願2014-512408  出願日:2013年3月

  11. レーザ加工方法、半導体部材製造方法、および半導体対象物

    田中敦之、笹岡千秋、天野浩、河口大祐、和仁陽太郎、伊ケ崎泰則

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    公開番号:公開特許20202102536  公開日:2020年7月

  12. 基板製造方法

    田中敦之、河口大祐

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    公開番号:公開特許 3674451  公開日:2020年7月

    出願国:外国  

  13. レーザ加工方法、半導体部材製造方法、および半導体対象物

    田中敦之、笹岡千秋、天野浩、河口大祐、和仁陽太郎、伊ケ崎泰則

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    公開番号:公開特許WO2020/130054  公開日:2020年6月

    出願国:外国  

  14. レーザ加工方法、半導体部材製造方法及びレーザ加工装置

    田中敦之、笹岡千秋、天野浩、河口大祐、和仁陽太郎、伊ケ崎泰則、油井俊樹

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    公開番号:公開特許WO2020/130055  公開日:2020年6月

    出願国:外国  

  15. 基板製造方法

    田中敦之、河口大祐

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    公開番号:公開特許 US2020/0180082  公開日:2020年6月

    出願国:外国  

  16. 基板製造方法

    田中敦之、河口大祐

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    公開番号:公開特許 CN111065765  公開日:2020年4月

    出願国:外国  

  17. 基板の製造方法

    田中敦之、河口大祐

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    公開番号:公開特許2019-043808  公開日:2019年3月

  18. 基板製造方法

    田中敦之、河口大祐

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    公開番号:公開特許 WO2019/044142  公開日:2019年3月

    出願国:外国  

  19. 炭化珪素半導体装置および炭化珪素半導体装置の製造方法

    田中敦之、辻崇

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    公開番号:公開特許2017-168674  公開日:2017年9月

  20. 炭化珪素半導体装置の製造方法および炭化珪素半導体装置

    俵武志、田中敦之

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    公開番号:公開特許2016-058499  公開日:2016年3月

  21. 炭化珪素半導体装置の製造方法

    田中敦之、辻崇

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    公開番号:公開特許2013-232555  公開日:2013年11月

  22. 縦型高耐圧半導体装置及びその製造方法

    田中敦之、岩室憲幸、原田信介

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    公開番号:再表2013/161420  公開日:2013年10月

  23. 炭化珪素半導体装置の製造方法

    田中敦之、福田憲司

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    公開番号:公開特許2013-247251  公開日:2013年10月

  24. 可動ゲート型電界効果トランジスタ

    熊田貴夫、江戸雅晴、河西公美、田中敦之

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    公開番号:公開特許2011-198916  公開日:2011年10月

  25. 炭化珪素半導体装置の製造方法

    田中敦之、岩室憲幸

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    特許番号/登録番号:特許第6074787  登録日:2017年1月 

  26. 炭化珪素半導体装置の製造方法および炭化珪素半導体装置

    田中敦之、俵武志

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    特許番号/登録番号:特許第6347188  登録日:2018年6月 

  27. 半導体装置の製造方法および製造装置

    田中敦之、辻崇

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    特許番号/登録番号:特許第6083129  登録日:2017年2月 

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