Faculty Profiles - AMANO, Hiroshi

Papers - AMANO, Hiroshi

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Growth of hexagonal boron nitride on sapphire substrate by pulsed-mode metalorganic vapor phase epitaxy

Xu Yang, Shugo Nitta, Kentaro Nagamatsu, Si-Young Bae, Ho-Jun Lee, Yuhuai Liu, Markus Pristovsek, Yoshio Honda, Hiroshi Amano

JOURNAL OF CRYSTAL GROWTH Vol. 482 ( 15 ) page： 1 - 8 2018.1

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Hexagonal boron nitride (h-BN) was directly grown on sapphire substrate using alternating ammonia (NH3) and triethylboron (TEB) supply (pulsed mode) in metalorganic vapor phase epitaxy. The best condition is when just enough NH3 is supplied to fully convert the TEB within one cycle. Excess NH3 caused islands on h-BN film surface while a lack of NH3 does not form h-BN at all. The epitaxial relationship between grown h-BN layer and c-plane sapphire was confirmed to be [0001](h-BN)||[0001](sapphire) and [10-10](h-BN)||[11-20](sapphire). It is known that, compared to AlN, BN requires higher V/III ratios for good crystallinity, which due to severe gas-phase reactions is difficult to achieve using continuous supply. Thus using pulsed mode the FWHM of the symmetric (0002) diffraction was almost halved and the growth rate was several times faster. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2017.10.036

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Electrical and Thermal Analysis of Vertical GaN-on-GaN PN Diodes

Yates Luke, Pavlidis Georges, Graham Samuel, Usami Shigeyoshi, Nagamatsu Kentaro, Honda Yoshio, Amano Hiroshi

PROCEEDINGS OF THE 17TH IEEE INTERSOCIETY CONFERENCE ON THERMAL AND THERMOMECHANICAL PHENOMENA IN ELECTRONIC SYSTEMS (ITHERM 2018) page： 831 - 837 2018

Theoretical Study of the Electronic Structure of Threading Edge Dislocations in GaN

Nakano Takashi, Araidai Masaaki, Shiraishi Kenji, Tanaka Atsushi, Honda Yoshio, Amano Hiroshi

GALLIUM NITRIDE AND SILICON CARBIDE POWER TECHNOLOGIES 8 Vol. 86 ( 12 ) page： 41 - 49 2018

DFT modeling of carbon incorporation in GaN(0001) and GaN(000(1)over-bar) metalorganic vapor phase epitaxy Reviewed

Pawel Kempisty, Yoshihiro Kangawa, Akira Kusaba, Kenji Shiraishi, Stanislaw Krukowski, Michal Bockowski, Koichi Kakimoto, and Hiroshi Amano

APPLIED PHYSICS LETTERS Vol. 111 page： 141602/1-5 2017.10

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

The carbon incorporation mechanism in GaN(0001) and GaN(000 (1) over bar) during MOVPE was investigated using density functional theory (DFT) calculations. The results confirm that the crucial factors for carbon incorporation are Fermi level pinning and accompanying surface band bending. In addition, the lattice symmetry has a strong dependence on the stability of carbon in a few subsurface layers, which results from interactions between the impurities and surface states. It was shown that these effects are responsible for facilitating or hindering the incorporation of impurities and dopants. The influence of diluent gas species (hydrogen or nitrogen) on carbon incorporation was discussed.

DOI： 10.1063/1.4991608

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

Liwen Sang, Bing Ren, Masatomo Sumiya, Meiyong Liao, Yasuo Koide, Atsushi Tanaka, Yujin Cho, Yoshitomo Harada, Toshihide Nabatame, Takashi Sekiguchi, Shigeyoshi Usami, Yoshio Honda, and Hiroshi Amano

APPLIED PHYSICS LETTERS Vol. 111 page： 122102/1-5 2017.9

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

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

Absolute technique for measuring internal electric fields in InGaN/GaN light-emitting diodes by electroreflectance applicable to all crystal orientations Reviewed

Tomoyuki Tanikawa, Kanako Shojiki, Ryuji Katayama, Shigeyuki Kuboya, Takashi Matsuoka, Yoshio Honda, and Hiroshi Amano

Applied Physics Express Vol. 10 page： 082101/1-4 2017.8

Low cost high voltage GaN polarization superjunction field effect transistors

H. Kawai, S. Yagi, S. Hirata, F. Nakamura, T. Saito, Y. Kamiyama, M. Yamamoto, H. Amano, V. Unni, E. M. S. Narayanan

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE Vol. 214 ( 8 ) page： 1600834/1-10 2017.8

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

A comprehensive overview of the novel high voltage GaN field effect transistors (FETs) based on the Polarization Superjunction (PSJ) concept, and a cost-effective approach towards manufacturing these high performance devices are presented. Current challenges impeding wider adoption of GaN power switching transistors in applications, and the latest results of the scaled-up PSJ-FETs from POWDEC KK, are also discussed. The article also presents hard-switching characteristics of 400-800V boost converter, constructed using a PSJ-FET grown on sapphire substrate, and the future direction of GaN power semiconductor technology based on monolithic integration for advanced power electronics.

DOI： 10.1002/pssa.201600834

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

Atsushi Tanaka, Ousmane1 Barry, Kentaro Nagamatsu, Junya Matsushita, Manato Deki, Yuto Ando, Maki Kushimoto, Shugo Nitta, Yoshio Honda, and Hiroshi Amano

Phys. Status Solidi A Vol. 214 ( 8 ) page： 1600829/1-5 2017.8

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

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

Effect of dislocations on the growth of p-type GaN and on the characteristics of p-n diodes Invited Reviewed

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

Phys. Status Solidi A Vol. 214 ( 8 ) page： 1600837/1-5 2017.8

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

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/pssb.201600722

Selective-area growth of doped GaN nanorods by pulsed-mode MOCVD: Effect of Si and Mg dopants Reviewed

Si-Young Bae, Kaddour Lekhal, Ho-Jun Lee, Jung-Wook Min, Dong-Seon Lee, Yoshio Honda, and Hiroshi Amano

Phys. Status Solidi B Vol. 254 ( 8 ) page： 1600722/1-7 2017.8

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

Injecting current with a uniform carrier concentration is important for applications with three-dimensional architectures such as vertical power devices or displays. In III-nitride nanostructures, dopants not only incorporate differently depending on the surface orientation but can also seriously affect the kinetic equilibrium shapes of the nanorods. Herein, we report selective-area growth of doped GaN nanorods grown by pulsed-mode metalorganic chemical vapor deposition. Two dopants, Si and Mg, were employed as donor and acceptor atoms, respectively, for a mono-doping approach. Furthermore, a mixed flow of Si and Mg was supplied for a co-doping approach. We compared the morphological effects and growth rates of each doped GaN nanorod array. Then, we proposed appropriate growth mechanisms for the doped GaN nanorods on the basis of our structural characterizations. These results might extend the morphological functionality of GaN nanorods by including doping and may also provide an appropriate foundation for the design of nanostructure-based electronic or photonic devices.

DOI： 10.1002/pssb.201600722

Decomposition of trimethylgallium and adduct formation in a metalorganic vapor phase epitaxy reactor analyzed by high-resolution gas monitoring system Reviewed

Kentaro Nagamatsu, Shugo Nitta, Zheng Ye, Hirofumi Nagao, Shinichi Miki, Yoshio Honda, and Hiroshi Amano

Phys. Status Solidi B Vol. 254 ( 8 ) page： 1600737/1-4 2017.8

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

Usami Shigeyoshi, Miyagoshi Ryosuke, Tanaka Atsushi, Nagamatsu Kentaro, Kushimoto Maki, Deki Manato, Nitta Shugo, Honda Yoshio, Amano Hiroshi

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE Vol. 214 ( 8 ) 2017.8

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

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Role of threading dislocations in strain relaxation during GaInN growth monitored by real-time X-ray reflectivity Reviewed

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

Applied Physics Letters Vol. 110 ( 26 ) page： 262105/1-5 2017.6

A-plane GaN growth on (11-20) 4H-SiC substrate with an ultrathin interlayer Reviewed

Zheng Sun, Peifeng Song, Shugo Nitta, Yoshio Honda, Hiroshi Amano

Journal of Crystal Growth Vol. 468 page： 866-869 2017.6

Selective-area growth of vertically oriented GaN nanostructures with a hafnium pre-orienting layer Reviewed

S.-Y.Bae, K. Lekhal, H.-J.Lee, T.Mitsunari, J.-W.Min, D.-S.Leed, M.Kushimoto, Y.Honda, H.Amano

Journal of Crystal Growth Vol. 468 page： 110-113 2017.6

Orientation-controlled epitaxial lateral overgrowth of semipolar GaN on Si(001) with a directionally sputtered AlN buffer layer Reviewed

Ho-Jun Lee, Si-Young Bae, Kaddour Lekhal, Akira Tamura, Takafumi Suzuki, Maki Kushimoto, Yoshio Honda, and Hiroshi Amano

Journal of Crystal Growth Vol. 468 page： 547-551 2017.6

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

Vol. 468 page： 552-556 2017.6

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

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

Annealing eﬀect on threading dislocations in a GaN grown on Si substrate Reviewed

Vol. 468 page： 835-838 2017.6

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

Eﬀect of rapid thermal annealing (RTA) on crystal defects in a GaN layer grown on a (111)Si substrate was investigated by photoluminescence (PL) and transmission electron microscopy (TEM) analyses. The PL spectra suggested that the density of gallium vacancy is not changed by the heat treatment up to 700 °C. In the TEM specimen, we had dislocation half loops generated by oﬀ-axis propagation of the threading dislocation. We found that the half-loop of c-type dislocation shrinks/moves by a repetitive RTA at 600–700 °C. In contrast, we could ﬁnd no remarkable changes in the a-type or a+c-type dislocations.

DOI： 10.1016/j.jcrysgro.2017.01.001

A-plane GaN growth on (11-20) 4H-SiC substrate with an ultrathin interlayer

Sun Zheng, Song Peifeng, Nitta Shugo, Honda Yoshio, Amano Hiroshi

JOURNAL OF CRYSTAL GROWTH Vol. 468 page： 866 - 869 2017.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Crystal Growth

A-plane GaN was attempted to be grown on (11-20) 4H-SiC bulk substrate without using a traditional thick buffer layer. By inducing TMAl treatment before the GaN growth step and using both a low pressure and V/III ratio, the interlayer thickness of the a-plane GaN/SiC was reduced to 1.7+0.5 nm. The ultrathin interlayer was observed to be either AlN or AlGaN with a low Ga composition. This study is aimed to contribute to the understanding of GaN growth on the sidewalls of c-plane trench structure SiC. The ultrathin growth technique is also hoped to be applied to the fabrication of GaN-based vertical structure nonpolar optical or electrical devices.

DOI： 10.1016/j.jcrysgro.2017.01.031

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Uneven AlGaN multiple quantum well for deep-ultraviolet LEDs grown on macrosteps and impact on electroluminescence spectral output Reviewed

Michiko Kaneda, Cyril Pernot, Yosuke Nagasawa, Akira Hirano, Masamichi Ippommatsu, Yoshio Honda, Hiroshi Amano, and Isamu Akasaki

Japanese Journal of Applied Physics Vol. 56 page： 061002 2017.5

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Papers - AMANO, Hiroshi