研究者詳細 - 天野　浩

論文 - 天野　浩

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天野浩

応用物理 90 巻 ( 7 ) 頁： 455 - 455 2021年7月

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天野浩

日本物理学会誌 76 巻 ( 7 ) 頁： 478 - 478 2021年7月

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

記述言語：日本語掲載種別：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

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

Amano, H

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 218 巻 ( 14 ) 2021年7月

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

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

APPLIED PHYSICS LETTERS 118 巻 ( 21 ) 2021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：Applied Physics Letters

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

DOI： 10.1063/5.0051552

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

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

Chemical science 12 巻 ( 22 ) 頁： 7713 - 7719 2021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：Chemical Science

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

DOI： 10.1039/d1sc01642c

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 ) 頁： SBBD03 2021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：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

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

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

APPLIED PHYSICS EXPRESS 14 巻 ( 5 ) 頁： 051003 2021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：Applied Physics Express

The electroluminescence (EL) uniformity of AlGaN-based deep UV laser diodes on AlN substrate was analyzed by using the EL imaging technique. Although nonuniform EL patterns were observed, the uniformity was improved by changing the position of the p-electrode. The threshold current density was also reduced by suppressing the inhomogeneity of the EL. Cathodoluminescence analysis revealed that the cause of the non-uniformity is the degradation of the active layer and the nonuniformity emission formed by rapid thermal annealing at high temperature after mesa structure formation.

DOI： 10.35848/1882-0786/abf443

Micro-Light Emitting Diode: From Chips to Applications

Parbrook, PJ; Corbett, B; Han, J; Seong, TY; Amano, H

LASER & PHOTONICS REVIEWS 15 巻 ( 5 ) 頁： 2000133 2021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：Laser and Photonics Reviews

Typical light-emitting diodes (LEDs) have a form factor >(300 × 300) µm2. Such LEDs are commercially mature in illumination and ultralarge displays. However, recent LED research includes shrinking individual LED sizes from side lengths >300 µm to values <100 µm, leading to devices called micro-LEDs. Their advent creates a number of exciting new application spaces. Here, a review of the principles and applications of micro-LED technology is presented. In particular, the implications of reduced LED size in necessitating mitigation strategies for nonradiative device edge damage as well as the potential for higher drive current densities are discussed. The opportunities to integrate micro-LEDs with electronics, and into large-scale arrays, allow pixel addressable scalable integrated displays, while the small micro-LED size is ideal for high-speed modulation for visible light communication, and for integration into biological systems as part of optogenetic therapies.

DOI： 10.1002/lpor.202000133

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

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

Journal of Applied Physics 129 巻 ( 16 ) 頁： 164503 2021年4月

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

Ga-rich zones created along macrosteps in n-AlGaN plausibly function as electron pathways of AlGaN-based deep-ultraviolet (DUV) LEDs fabricated on AlN templates using 1.0°-miscut c(0001) sapphire substrates toward the m[1-100] axis. This work was performed to clarify AlN mole fractions (xAl) of Ga-rich zones. xAl ≃ (7/12, 6/12, and 5/12) was observed in Ga-rich zones in AlαGa1−αN (α ≃ 0.63, 0.55, and 0.43, respectively) by the method proposed in our previous article in which we showed that Ga-rich zones of Al8/12Ga4/12N were created in Al0.7Ga0.3N. xAl in the Ga-rich zones obtained from an energy-dispersive x-ray signal by scanning transmission electron microscopy calibrated by Rutherford backscattering well agreed with xAl obtained by cross-sectional cathodoluminescence (CL) spectroscopy using scanning electron microscopy. A weak CL shoulder peak corresponding to Al4/12Ga8/12N was also observed for Al0.43Ga0.57N. In addition, xAl ≃ n/12 (n = 6-9) in Al-rich zones appeared in the rest of the Ga-rich zones. Furthermore, nanobeam electron diffraction patterns of the Ga-rich zones indicated a high possibility of a regular configuration of Ga and Al atoms on the c(0001) plane in our samples. Consequently, xAl values in nonflat AlGaN layers with macrosteps were often determined to be near n/12 (n: integer). Thus, Ga-rich zones (xAl = n/12: n = 4-8) formed in our nonflat AlGaN layers, which originated from the macrosteps along [11-20] edgelines normal to the m[1-100] axis, are suggested to be metastable. The creation of discrete xAl in Ga-rich zones should contribute to the stable production of DUV-LEDs using high-miscut sapphire substrates.

DOI： 10.1063/5.0042036

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 ) 頁： 046501 2021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 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

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

Sim, KB; Kim, SK; Lee, HS; Lee, SY; Seong, TY; Amano, H

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY 10 巻 ( 4 ) 頁： 045005 2021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：ECS Journal of Solid State Science and Technology

We optimized Ni/Ag-based p-type reflectors for the improvement of efficiency of 273 nm deep ultraviolet (DUV) AlGaN-based flip-chip light emitting diodes (FCLEDs). The Ni(3 nm)/Ag(5-15 nm)/Al/Ni and Ni(25-50 nm)/Ag/Ni contacts exhibited higher reflectance (36.4-39.5%) at 273 nm than reference Ni(5 nm)/Au(5 nm)/Al/Ni contact (26.1%). The Ni(3 nm)/Ag/Al(200 nm)/Ni(20 nm) and Ni/Ag(200 nm)/Ni(20 nm)-based FCLEDs gave forward voltages in the rage of 6.93-7.11 V and 5.5-6.28 V at 20 mA, respectively, whereas the Ni/Au-based sample showed 6.35 V. Further, the Ni(3 nm)/Ag(10 nm)/Al/Ni-based and Ni(50 nm)/Ag(200 nm)/Ni-based samples exhibited 4.85% and 13.4% larger output power at 1.2 W than the reference sample. The Ni(3 nm)/Ag(10 nm)-based and Ni(50 nm)/Ag(200 nm)/Ni-based samples produced 5.6% and 8.5% higher peak external quantum efficiency than the reference sample. It was further shown that the Ni(3 nm)/Ag(10 nm)/Al/Ni-based and Ni(50 nm)/Ag(200 nm)/Ni-based samples experienced less efficiency droop (namely, 27.9 and 26.4%, respectively) than the reference sample (31.4%). Based on the scanning transmission electron microscopy and X-ray photoemission spectroscopy results, the ohmic formation mechanism is described and discussed.

DOI： 10.1149/2162-8777/abf49b

Numerical Simulation of Ammonothermal Crystal Growth of GaN-Current State, Challenges, and Prospects

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

CRYSTALS 11 巻 ( 4 ) 頁： 356 2021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：Crystals

Numerical simulations are a valuable tool for the design and optimization of crystal growth processes because experimental investigations are expensive and access to internal parameters is limited. These technical limitations are particularly large for ammonothermal growth of bulk GaN, an important semiconductor material. This review presents an overview of the literature on simulations targeting ammonothermal growth of GaN. Approaches for validation are also reviewed, and an overview of available methods and data is given. Fluid flow is likely in the transitional range between laminar and turbulent; however, the time-averaged flow patterns likely tend to be stable. Thermal boundary conditions both in experimental and numerical research deserve more detailed evaluation, especially when designing numerical or physical models of the ammonothermal growth system. A key source of uncertainty for calculations is fluid properties under the specific conditions. This originates from their importance not only in numerical simulations but also in designing similar physical model systems and in guiding the selection of the flow model. Due to the various sources of uncertainty, a closer integration of numerical modeling, physical modeling, and the use of measurements under ammonothermal process conditions appear to be necessary for developing numerical models of defined accuracy.

DOI： 10.3390/cryst11040356

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

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

SCIENTIFIC REPORTS 11 巻 ( 1 ) 頁： 6754 2021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：Scientific Reports

GaN nanorods (NRds) with axial InGaN/GaN MQWs insertions are synthesized by an original cost-effective and large-scale nanoimprint-lithography process from an InGaN/GaN MQWs layer grown on c-sapphire substrates. By design, such NRds exhibit a single emission due to the c-axis MQWs. A systematic study of the emission of the NRds by time-resolved luminescence (TR-PL) and power dependence PL shows a diameter-controlled luminescence without significant degradation of the recombination rate thanks to the diameter-controlled strain tuning and QSCE. A blueshift up to 0.26 eV from 2.28 to 2.54 eV (543 nm to 488 nm) is observed for 3.2 nm thick InGaN/GaN QWs with an In composition of 19% when the NRds radius is reduced from 650 to 80 nm. The results are consistent with a 1-D based strain relaxation model. By combining state of the art knowledge of c-axis growth and the strong strain relieving capability of NRds, this process enables multiple and independent single-color emission from a single uniform InGaN/GaN MQWs layer in a single patterning step, then solving color mixing issue in InGaN based nanorods LED devices.

DOI： 10.1038/s41598-021-86139-9

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

Kangawa, Y; Kusaba, A; Kempisty, P; Shiraishi, K; Nitta, S; Amano, H

CRYSTAL GROWTH & DESIGN 21 巻 ( 3 ) 頁： 1878 - 1890 2021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：Crystal Growth and Design

To improve the properties of semiconductors, it is necessary to construct an integrated crystal growth model that covers all elementary processes of metal-organic vapor phase epitaxy (MOVPE). Although there are several theoretical models that can reproduce any elemental growth process, they are inadequate for controlling semiconductor epitaxy: the elementary processes of (1) the vapor phase reaction, (2) the surface reaction, and (3) incorporation are entangled with each other. That is, sequential analyses of elementary growth processes from upstream (1) to downstream (3) are indispensable for an understanding of the entire process of MOVPE. In this Review, the recent progress of theoretical models based on calculations from first-principles calculations are summarized. The possibility of predicting carbon concentrations in GaN grown by MOVPE are explored as an example. The results of calculations using a model that integrates (1) → (2) → (3) reproduce the experimental tendencies of carbon incorporation. Calculations show that the contribution of each elementary growth process to a change in carbon concentration can be discussed separately, but the relationship between the input parameters and the resulting outputs can only be determined through experiment. Although this examination explores a special case, the development of a precise integrated crystal growth model would greatly contribute to innovation in semiconductor manufacturing.

DOI： 10.1021/acs.cgd.0c01564

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 ) 頁： 036505 2021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：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

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

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

CRYSTALS 11 巻 ( 3 ) 頁： 1 - 27 2021年3月

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

Thermal boundary conditions for numerical simulations of ammonothermal GaN crystal growth are investigated. A global heat transfer model that includes the furnace and its surroundings is presented, in which fluid flow and thermal field are treated as conjugate in order to fully account for convective heat transfer. The effects of laminar and turbulent flow are analyzed, as well as those of typically simultaneously present solids inside the autoclave (nutrient, baffle, and multiple seeds). This model uses heater powers as a boundary condition. Machine learning is applied to efficiently determine the power boundary conditions needed to obtain set temperatures at specified locations. Typical thermal losses are analyzed regarding their effects on the temperature distribution inside the autoclave and within the autoclave walls. This is of relevance because autoclave wall temperatures are a convenient choice for setting boundary conditions for simulations of reduced domain size. Based on the determined outer wall temperature distribution, a simplified model containing only the autoclave is also presented. The results are compared to those observed using heater-long fixed temperatures as boundary condition. Significant deviations are found especially in the upper zone of the autoclave due to the important role of heat losses through the autoclave head.

DOI： 10.3390/cryst11030254

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

Yasuda, H; Nishitani, T; Ichikawa, S; Hatanaka, S; Honda, Y; Amano, H

QUANTUM BEAM SCIENCE 5 巻 ( 1 ) 頁： 5 2021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：Quantum Beam Science

The development of pulsed electron sources is applied to electron microscopes or electron beam lithography and is effective in expanding the functions of such devices. The laser photocathode can generate short pulsed electrons with high emittance, and the emittance can be increased by changing the cathode substrate from a metal to compound semiconductor. Among the substrates, nitride-based semiconductors with a negative electron affinity (NEA) have good advantages in terms of vacuum environment and cathode lifetime. In the present study, we report the development of a photocathode electron gun that utilizes photoelectron emission from a NEA-InGaN substrate by pulsed laser excitation, and the purpose is to apply it to material nanofabrication and high-speed observation using a pulsed transmission electron microscope (TEM) equipped with it.

DOI： 10.3390/qubs5010005

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 ) 頁： 072103 2021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：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

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

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

OPTICAL MATERIALS EXPRESS 11 巻 ( 2 ) 頁： 524 - 524 2021年2月

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