研究者詳細 - 天野　浩

論文 - 天野　浩

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単結晶AlN 基板を用いたUV-C 波長域レーザーダイオード Open Access

張梓懿, 久志本真希, 吉川陽, 笹岡千秋, 天野浩

レーザー研究 52 巻 ( 1 ) 頁： 6 2024年

Anisotropic hole transport along [0001] and [1120] direction in p-doped (1010) GaN 査読有り Open Access

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

JOURNAL OF APPLIED PHYSICS 134 巻 ( 23 ) 2023年12月

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

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

DOI： 10.1063/5.0177681

Electron lifetime and diffusion coefficient in dopant-free p-type distributed polarization doped AlGaN 査読有り Open Access

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

APPLIED PHYSICS LETTERS 123 巻 ( 25 ) 2023年12月

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

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

DOI： 10.1063/5.0180062

Ga-polar GaN Camel diode enabled by a low-cost Mg-diffusion process 査読有り Open Access

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

APPLIED PHYSICS EXPRESS 16 巻 ( 12 ) 2023年12月

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

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

DOI： 10.35848/1882-0786/ad0db9

Using low-temperature growth to resolve the composition pulling effect of UV-C LEDs 査読有り Open Access

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

APPLIED PHYSICS LETTERS 123 巻 ( 22 ) 2023年11月

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

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

DOI： 10.1063/5.0183320

Multiplexing of bias-controlled modulation modes on a monolithic III-nitride optoelectronic chip 査読有り

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

OPTICS LETTERS 48 巻 ( 19 ) 頁： 5069 - 5072 2023年10月

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

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

DOI： 10.1364/OL.503429

Dislocation Suppresses Sidewall-Surface Recombination of Micro-LEDs 査読有り

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

LASER & PHOTONICS REVIEWS 17 巻 ( 10 ) 2023年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Laser and Photonics Reviews

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

DOI： 10.1002/lpor.202300199

UV/DUV light emitters 査読有り Open Access

Khan, A; Kneissl, M; Amano, H

APPLIED PHYSICS LETTERS 123 巻 ( 12 ) 2023年9月

Impact of graphene state on the orientation of III-nitride 査読有り

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

APPLIED PHYSICS LETTERS 123 巻 ( 12 ) 2023年9月

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

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

DOI： 10.1063/5.0157588

Investigation of Electrical Properties of N-Polar AlGaN/AlN Heterostructure Field-Effect Transistors 査読有り

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

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 220 巻 ( 16 ) 2023年8月

記述言語：英語掲載種別：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

Inactivation characteristics of a 280 nm Deep-UV irradiation dose on aerosolized SARS-CoV-2 査読有り Open Access

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

ENVIRONMENT INTERNATIONAL 177 巻頁： 108022 2023年7月

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

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

DOI： 10.1016/j.envint.2023.108022

Stress relaxation of AlGaN on nonpolar m-plane GaN substrate 査読有り Open Access

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

JOURNAL OF APPLIED PHYSICS 133 巻 ( 22 ) 2023年6月

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

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

DOI： 10.1063/5.0149838

Impact of Sidewall Conditions on Internal Quantum Efficiency and Light Extraction Efficiency of Micro-LEDs 査読有り Open Access

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

ADVANCED OPTICAL MATERIALS 11 巻 ( 10 ) 2023年5月

記述言語：英語掲載種別：研究論文（学術雑誌）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

Lateral p-type GaN Schottky barrier diode with annealed Mg ohmic contact layer demonstrating ideal current-voltage characteristic 査読有り

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

APPLIED PHYSICS LETTERS 122 巻 ( 14 ) 2023年4月

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

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

DOI： 10.1063/5.0146080

Simultaneous light emission and detection of an AlGaInP quantum well diode 査読有り Open Access

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

AIP ADVANCES 13 巻 ( 4 ) 2023年4月

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 Advances

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

DOI： 10.1063/5.0142093

2D-GaN/AlN Multiple Quantum Disks/Quantum Well Heterostructures for High-Power Electron-Beam Pumped UVC Emitters. 査読有り Open Access

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

Nanomaterials (Basel, Switzerland) 13 巻 ( 6 ) 2023年3月

A Review on the Progress of AlGaN Tunnel Homojunction Deep-Ultraviolet Light-Emitting Diodes 招待有り査読有り Open Access

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

CRYSTALS 13 巻 ( 3 ) 2023年3月

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

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

DOI： 10.3390/cryst13030524

Temperature Field, Flow Field, and Temporal Fluctuations Thereof in Ammonothermal Growth of Bulk GaN-Transition from Dissolution Stage to Growth Stage Conditions. 査読有り Open Access

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

Materials (Basel, Switzerland) 16 巻 ( 5 ) 2023年2月

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

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

DOI： 10.3390/ma16052016

Red emission from InGaN active layer grown on nanoscale InGaN pseudosubstrates 査読有り

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

JAPANESE JOURNAL OF APPLIED PHYSICS 62 巻 ( 2 ) 2023年2月

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

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

DOI： 10.35848/1347-4065/acb74c

平板捕集電極をもつ電気集塵装置の粒子捕集特性 Open Access

高牟礼光太郎, 岩谷靖雅, 天野浩, 八木哲也, 内山知実

年次大会 2023 巻 ( 0 ) 頁： S054-05 2023年

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