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151. Discrete wavelengths observed in electroluminescence originating from Al1/2Ga1/2N and Al1/3Ga2/3N created in nonflat AlGaN quantum wells.

Author

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

Subjects
QUANTUM wells, ELECTROLUMINESCENCE, LIGHT emitting diodes, WAVELENGTHS, NATURAL numbers, GAS flow
Abstract

When nonflat AlxGa1−xN quantum wells (QWs) for producing 285 nm light emitting diodes (LEDs) were fabricated on n-AlGaN on AlN templates with dense macrosteps on c(0001) sapphire substrates with a 1.0° miscut relative to the m[1–100] axis, composite electroluminescence (EL) spectra from both inclined and terrace zones in AlxGa1−xN QWs (x∼ 1/3) were generated owing to compositional and thickness modulations. The shoulder or main peaks in composite EL spectra tended to locate at fixed discrete wavelengths of ∼287, ∼292, and ∼296 nm from 12 nonuniform 285 nm LED wafers that were involved in nonnegligible run-to-run drift, even though these wafers were fabricated using the same source gas flow parameters for metal-organic vapor phase epitaxy. The discrete wavelengths of ∼287, ∼292, and ∼296 nm were attributed to EL from Al1/3Ga2/3N QWs with thicknesses of 8, 9, and 10 monolayers (ML), respectively, by referring to the results of cathodoluminescence (CL) analysis. Also, when nonflat AlxGa1−xN QWs (x∼ 1/2) for 265 nm LEDs were grown, single-peak-like EL spectra were mainly generated from the inclined zones in nonflat QWs. The EL spectra taken from four nonuniform 265 nm LED wafers tended to show weak structures or main peaks at ∼257, ∼261, ∼266, and ∼271 nm, which were also attributed to emissions from Al1/2Ga1/2N QWs with thicknesses of 5, 6, 7, and 8 ML, respectively, by referring to CL analysis results. The creation of Al1/3Ga2/3N and Al1/2Ga1/2N in nonflat QWs in this work was in agreement with the results of our previous studies that indicated the creation of metastable Aln/12Ga1−n/12N (n: consecutive natural numbers). Furthermore, QW thicknesses of consecutive n ML may imply that Al1/3Ga2/3N and Al1/2Ga1/2N have 1 ML configurations of Al and Ga atoms on a c(0001) plane. [ABSTRACT FROM AUTHOR]

Published
2021
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153. Suppression of Green Luminescence of Mg-Ion-Implanted GaN by Subsequent Implantation of Fluorine Ions at High Temperature

Author

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

Abstract

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. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Published
2019

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

Author

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

Abstract

Recessed-gate AlGaN/GaN metal-insulator-semiconductor (MIS) high electron mobility transistors (HEMTs) were fabricated by utilizing a photoelectrochemical (PEC) etching and a post-metallization annealing (PMA) process. In order to demonstrate the device performance and reliability, both electrical and optical electroluminescence (EL) properties were evaluated. The capacitance-voltage (C-V) characteristic showed that the PEC etching and subsequent PMA process enhanced the gate control of two-dimensional electron gas density. The PEC-etched-gate AlGaN/GaN MIS-HEMT showed the smallest sub-threshold slope of all the samples including planar-gate and inductively coupled plasma-etchedgate devices. Furthermore, the PEC-etched devices showed an extremely low 10(-11) A mm(-1) gate leakage current with no spot-like EL. These results indicated that the PEC etching and subsequent PMA process improved the electrical properties of the Al2O3/AlGaN interface, resulting in enhanced device performance of the AlGaN/GaN MIS-HEMTs. (C) 2019 The Japan Society of Applied Physics

Published
2019

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

Author

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

Abstract

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.

Published
2019

156. Vertical GaN p+-n junction diode with ideal avalanche capability grown by halide vapor phase epitaxy.

Author

Ohnishi, Kazuki, Kawasaki, Seiya, Fujimoto, Naoki, Nitta, Shugo, Watanabe, Hirotaka, Honda, Yoshio, and Amano, Hiroshi

Subjects
GALLIUM nitride, AVALANCHE diodes, BREAKDOWN voltage, EPITAXY, GASES, AVALANCHES
Abstract

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

Published
2021
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157. Serial changes of plasma plasminogen activator inhibitor activity in acute myocardial infarction: difference between thrombolytic therapy and direct coronary angioplasty

Author

Hirashima, Osamu, Ogawa, Hisao, Oshima, Shuichi, Sakamoto, Tomohiro, Honda, Yoshio, Sakata, Shinji, Masuda, Takenobu, Miyao, Yuji, and Yasue, Hirofumi

Subjects
Thrombolytic therapy -- Physiological aspects, Angioplasty -- Physiological aspects, Tissue plasminogen activator -- Physiological aspects, Health
Published
1995

158. Impact of gate electrode formation process on Al2O3/GaN interface properties and channel mobility.

Author

Ando, Yuto, Deki, Manato, Watanabe, Hirotaka, Taoka, Noriyuki, Tanaka, Atsushi, Nitta, Shugo, Honda, Yoshio, Yamada, Hisashi, Shimizu, Mitsuaki, Nakamura, Tohru, and Amano, Hiroshi

Abstract

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. [ABSTRACT FROM AUTHOR]

Published
2021
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181. In situ X-ray investigation of changing barrier growth temperatures on InGaN single quantum wells in metal-organic vapor phase epitaxy.

Author

Ju, Guangxu, Honda, Yoshio, Tabuchi, Masao, Takeda, Yoshikazu, and Amano, Hiroshi

Subjects
*INDIUM gallium nitride, *QUANTUM wells, *CRYSTAL growth, *VAPOR phase epitaxial growth, *X-ray diffractometers, *PHOTOLUMINESCENCE
Abstract

The effects of GaN quantum barriers with changing growth temperatures on the interfacial characteristics of GaN/InGaN single quantum well (SQW) grown on GaN templates by metalorganic vapour phase epitaxy were in situ investigated by X-ray crystal truncation rod (CTR) scattering and X-ray reflectivity measurements at growth temperature using a laboratory level X-ray diffractometer. Comparing the curve-fitting results of X-ray CTR scattering spectra obtained at growth temperature with that at room temperature, the InxGa1-xN with indium composition less than 0.11 was stabile of the indium distribution at the interface during the whole growth processes. By using several monolayers thickness GaN capping layer to protect the InGaN well layer within temperature-ramping process, the interfacial structure of the GaN/InGaN SQW was drastically improved on the basis of the curve-fitting results of X-ray CTR scattering spectra, and the narrow full width at half-maximum and strong luminous intensity were observed in room temperature photoluminescence spectra. [ABSTRACT FROM AUTHOR]

Published
2014
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182. Detailed analysis of Ga-rich current pathways created in an n-Al0.7Ga0.3N layer grown on an AlN template with dense macrosteps.

Author

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

Abstract

To clarify the behavior of the AlGaN in 20 nm wide Ga-rich current pathways in an n-AlGaN layer, which assists carrier localization in AlGaN-based light-emitting diodes, we performed a detailed analysis using an n-Al0.7Ga0.3N layer on AlN with dense macrosteps on a 1.0° miscut sapphire substrate. Energy-dispersive X-ray spectra, obtained using cross-sectional scanning transmission electron microscopy calibrated by Rutherford backscattering and cross-sectional cathodoluminescence spectra, indicated that AlN mole fraction in the Ga-rich current pathways was nearly ~2/3. This result is consistent with those of other research groups, suggesting that metastable Al2/3Ga1/3N is created in Ga-rich current pathways. [ABSTRACT FROM AUTHOR]

Published
2020
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183. III-nitride-based photovoltaic applications on silicon: Comparison between axial and coreshell InGaN nanowire devices

Author

Lekhal, Kaddour, Avit, Geoffrey, Baa, Si-Young, Lee, Ho-Jun, Barry, Oussman, Roche, Elissa, andre, yamina, Honda, Yoshio, Trassoudaine, Agnès, Amano, Hiroshi, Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya University, Institut Pascal (IP), SIGMA Clermont (SIGMA Clermont)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS), Department of Electrical Engineering and Computer Science [Nagoya], and Avit, Geoffrey

Subjects
[PHYS]Physics [physics], [SPI]Engineering Sciences [physics], [SPI] Engineering Sciences [physics], [SPI.NANO] Engineering Sciences [physics]/Micro and nanotechnologies/Microelectronics, [PHYS.COND]Physics [physics]/Condensed Matter [cond-mat], [SPI.NANO]Engineering Sciences [physics]/Micro and nanotechnologies/Microelectronics, [PHYS.COND] Physics [physics]/Condensed Matter [cond-mat], [PHYS] Physics [physics]
Abstract

International audience; Solar cells are one of the major source of renewable energy available today. InGaN alloys are promising candidates for future solar cells due to their direct tunable bandgap between 0.7 eV and 3.4 eV, covering major absorption range of solar spectrum. However, the conversion efficiency of InGaN-based solar cells remains limited because of the poor crystalline quality of thick InGaN layers, particularly at high indium composition. In this work, to overcome this limit, we propose two structures based on InGaN core?shell and axial InGaN nanowires. We performed the hydride vapor phase epitaxy (HVPE) to directly grow n-type GaN wires and InGaN nanowires on p-type silicon substrate. The metalorganic vapor phase epitaxy (MOCVD) was applied to grow the InGaN core?shell structure. The energy dispersive X-ray spectroscopy (EDS) and cathodoluminescence measurements revealed that nanowires grown on silicon exhibit an uniform indium distribution of ~ 40?50 %, with an ideal bandgap configuration of InGaN 1.8 eV/Si 1.12 eV for high conversion efficiency. Then, the photovoltaic properties of the fabricated solar cells were assessed. As a consequence, short-circuit current density and open-circuit voltage were typically ~20 µA/cm2 and 0.1 V under a 1 sun (1.5 AMG) illumination, respectively. Even though, the efficiency measured was still low, this work suggests the potential of directly integrated InGaN nanowires on silicon for solar cell applications.

Published
2017

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

Author

Honda, Anna, Watanabe, Hirotaka, Takeuchi, Wakana, Honda, Yoshio, Amano, Hiroshi, and Kato, Takeshi

Abstract

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

Published
2024
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187. Visualization of different carrier concentrations in n-type-GaN semiconductors by phase-shifting electron holography with multiple electron biprisms.

Author

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

Subjects
ELECTRON holography, CARRIER density, TRANSMISSION electron microscopes, SEMICONDUCTORS, HOLOGRAPHY, N-type semiconductors
Abstract

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. [ABSTRACT FROM AUTHOR]

Published
2020
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