Faculty Profiles - AMANO, Hiroshi

Papers - AMANO, Hiroshi

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Epitaxial growth of GaN by REMOCVD in the downflow of a very high frequency(VHF) N2/H2 excited plasma Reviewed

Yi Lu, Hiroki Kondo,Kenji Ishikawa,Osamu Oda,KeigoTakeda,Makoto Sekine, Hiroshi Amano,Masaru Hori

Journal of Crystal Growth Vol. 391 page： 97-103 2014.4

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

We found that this REMOCVD allowed the growth of epitaxial GaN films of the wurtzite structure of (0001) orientation on sapphire substrates with a high growth rate of 0.42 μm/h at a low temperature of 800 °C. The present REMOCVD is a promising method for GaN growth at relatively low temperature and without using costly ammonia gas.

DOI： 10.1016/j.jcrysgro.2014.01.014

Growth of InGaN/GaN multiple quantum wells on size-controllable nanopyramid arrays Reviewed

Cao Miao, Yoshio Honda, Masahito Yamaguchi and Hiroshi Amano

Japanese Journal of Applied Physics Vol. 53 page： 0303060 2014.3

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

Regularly distributed nanopyramid arrays with a highly uniform size were grown by selective-area growth. The nanopyramid size could be tuned by varying the growth time. Two emission peaks were observed from multiple quantum wells grown on the nanopyramids. The longer-wavelength peak originated from the apexes of pyramids with threefold symmetry. High-density stacking faults observed at these triangular apexes might be responsible for the higher indium incorporation. The formation of embedded voids inside the pyramids was explained by the different growth rates at the edge and center of the mask window caused by the low diffusion length.

DOI： 10.7567/JJAP.53.030306

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

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

Journal of Applied Physics Vol. 115 page： 094906 2014.3

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

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.

DOI： 10.1063/1.4867640

Multijunction GaInN-based solar cells using a tunnel junction Reviewed

Hironori Kurokawa, Mitsuru Kaga, Tomomi Goda, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki and Hiroshi Amano

Applied Physics Express Vol. 7 ( 3 ) page： 034104 2014.3

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

We fabricated and characterized a two-junction GaInN-based solar cell using a tunnel junction fabricated by crystal growth. This solar cell has two active layers with a differing bandgap energy corresponding to blue or green light. We confirmed that the open-circuit voltage (VOC) in this solar cell was increased by the series connection using the tunnel junction. The short-circuit current density, VOC, fill factor, and energy conversion efficiency of this solar cell were 0.28 mA/cm2, 3.0 V, 0.5, and 0.41%, respectively, under an air mass filter of 1.5 G at 1-sun irradiation and room temperature.

DOI： 10.7567/APEX.7.034104

Novel activation process for Mg-implanted GaN Reviewed

Shin Hashimoto, Takao Nakamura, Yoshio Honda, Hiroshi Amano

Journal of Crystal Growth Vol. 388 page： 112-115 2014.2

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

A novel activation process for Mg-implanted GaN was demonstrated. As opposed to the conventional thermal annealing process, an H2/NH3 alternating supply annealing process achieved better optical activation, stronger near-ultraviolet luminescence and weaker yellow luminescence in the photoluminescence spectroscopy. After this process, small hexagonal hillocks were observed on the surface, which indicated that crystal regrowth was induced by this process, consisting of decomposition of GaN by H2 supplies and re-crystallization by NH3 supplies. It was revealed that the implanted Mg could easily be located at the activation site by means of crystal regrowth by this process.

DOI： doi:10.1016/j.jcrysgro.2013.07.011

Properties of the main Mg-related acceptors in GaN from optical and structural studies Reviewed

B. Monemar, P. P. Paskov, G. Pozina, C. Hemmingsson, J. P. Bergman, S. Khromov, V. N. Izyumskaya, V. Avrutin, X. Li, H. Morkoç, H. Amano, M. Iwaya, and I. Akasaki

Journal of Applied Physics Vol. 115 page： 053507 2014.2

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

The luminescent properties of Mg-doped GaN have recently received particular attention, e.g., in the
light of new theoretical calculations, where the deep 2.9 eV luminescence band was suggested to be
the main optical signature of the substitutional MgGa acceptor, thus, having a rather large binding
energy and a strong phonon coupling in optical transitions. We present new experimental data on
homoepitaxial Mg-doped layers, which together with the previous collection of data give an
improved experimental picture of the various luminescence features in Mg-doped GaN.

DOI： 10.1063/1.4862928

Growth of low-defect-density nonpolar a-plane GaN on r-plane sapphire using pulse NH3 interrupted etching Reviewed

Ji-Su Son, Yoshio Honda, and Hiroshi Amano

Optics Express Vol. 22 ( 3 ) page： 3585-3592 2014.2

Morphology development of GaN nanowires using a pulsed-mode MOCVD growth technique Reviewed

Byung Oh Jung, Si-Young Bae, Yoshihiro Kato, Masataka Imura, Dong-Seon Lee, Yoshio Honda and Hiroshi Amano

CrystEngComm Vol. 16 page： 2273-2282 2014.1

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

we demonstrate a scalable process for the precise position-controlled selective growth of
GaN nanowire arrays by metalorganic chemical vapor deposition (MOCVD) using a pulsed-mode growth
technique. The location, orientation, length, and diameter of each GaN nanowire are controlled via
pulsed-mode growth parameters such as growth temperature and precursor injection and interruption
durations.

DOI： 10.1039/c3ce42266f

Characteristics of a-plane GaN films grown on optimized silicon-dioxide-patterned r-plane sapphire substrates Reviewed

Ji-Su Son, Y. Honda, M. Yamaguchi, H. Amano, K. H. Baik, Y. G. Seo and S. M. Hwang

Thin Solid Films Vol. 546 ( 11 ) page： 108-113 2013.11

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

We report on the characteristics of a-plane GaN films directly grown on optimized silicon-dioxide-patterned r-plane sapphire substrates. Various shapes and sizes of silicon dioxide patterns were considered with the aim of achieving fully coalescent a-plane GaN films with a smooth surface and high crystalline quality. The omega full widths at half maximum of the X-ray rocking curve values of optimized a-plane GaN films with regular hexagonal patterns of 1 micron window width and 6 micron mask width were measured to be 597 arcsec along the c-axis direction and 457 arcsec along the m-axis direction. Atomic force microscopy images revealed a significant reduction in the density of submicron pits in the mask region.

Effects of exciton localization on internal quantum efficiency of InGaN nanowires Reviewed

Hideaki Murotani, Yoichi Yamada, Takuya Tabata, Yoshio Honda, Masahito Yamaguchi and Hiroshi Amano

Journal of Applied Physics Vol. 114 page： 153506 2013.10

Strain-Compensated Effect on the Growth of InGaN/AlGaN Multi-Quantum Well by Metalorganic Vapor Phase Epitaxy Reviewed

Tomohiro Doi, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JB14 2013.8

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

InGaN/AlGaN multi-quantum wells (MQWs) were grown by metalorganic vapor phase epitaxy. The In composition of the InGaN well layer was found to increase with the tensile strain of the AlGaN barrier layer. The InGaN/AlGaN strain-compensated structure can be grown at a higher growth temperature than that of the InGaN/GaN MQW, which shows that the same emission wavelength and thus the density of the V-defects can be effectively suppressed.

DOI： 10.7567/JJAP.52.08JB14

GaN Overgrowth on Thermally Etched Nanoporous GaN Template Reviewed

Cao Miao, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JB03 2013.8

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

A thermal-etching process for fabricating nanoporous GaN templates in a metalorganic vapor phase epitaxy (MOVPE) reactor was proposed. Such nanoporous templates exhibited nearly complete strain relaxation and considerably increased photoluminescence (PL) intensity. The threading dislocation density (TDD) after overgrowth was reduced from 3 ×109 to 4 ×108 cm-2 for the template with poor quality, whereas little improvement was observed for the high-quality template (TDD, 4 ×108 cm-2). Multiple quantum wells (MQWs) grown on a nanoporous template fabricated from the high-quality GaN template were used to assess the effect on LED performance. The PL intensity of the sample with a nanoporous structure showed a twofold increase in PL intensity compared with the control sample.

DOI： 10.7567/JJAP.52.08JB03

Growth of GaN on Si(111) Substrates via a Reactive-Sputter-Deposited AlN Intermediate Layer Reviewed

Takaya Yamada, Tomoyuki Tanikawa, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

Japanese Journal of Applied Physics Vol. 52 page： 08JB16 2013.8

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

GaN films were successfully grown on Si(111) substrates using a reactive-sputter-deposited AlN intermediate layer (sp-AlN) at 350 °C. Uniform GaN growth was obtained with the pre sputtering of a thin Al film before the deposition of sp-AlN. Atomic force microscopy (AFM) measurements revealed that the density of pits originating from the ends of mixed/screw-type dislocations is about 109 cm-2, which is much lower than that of GaN grown on a metalorganic vapor phase epitaxy (MOVPE) deposited AlN intermediate layer. The decrease in the pit density might have originated from the small number of initial nuclei of GaN.

DOI： 10.7567/JJAP.52.08JB16

Fabrication of InGaN/GaN Multiple Quantum Wells on (1-101) GaN Reviewed

Tomoyuki Tanikawa, Tomotaka Sano, Maki Kushimoto, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JC05 2013.8

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

InGaN/GaN multiple quantum wells (MQWs) on semipolar (1101) GaN microstripes on a Si substrate were fabricated and their optical properties were investigated. From cathodoluminescence (CL) analysis, strong CL emission was obtained in an MQW emitting at 433 nm. However, dark lines appeared in MQWs emitting at longer wavelengths. These dark lines are attributed to lattice relaxation and the generation of misfit dislocations and stacking faults in an MQW, resulting in nonradiative centers. The internal quantum efficiency (IQE) was estimated from excitation-power-dependent photoluminescence analysis. The (1101) InGaN/GaN MQW had a high IQE owing to the high crystalline quality of the underlying GaN and the reduced piezoelectric field. The IQE at a carrier concentration of 1×1018 cm-3 in a sample emitting at 490 nm was as high as 90%. The efficiency decreased in a sample with a higher indium content in the MQW due to the generation of misfit dislocations and stacking faults.

DOI： 10.7567/JJAP.52.08JC05

Stacking Faults and Luminescence Property of InGaN Nanowires Reviewed

Takuya Tabata, Jihyun Paek, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JE06 2013.8

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

InGaN nanowires (NWs) were grown on (111)Si substrate using radio-frequency plasma-assisted molecular beam epitaxy, and the density of the stacking faults (SFs) in the InGaN NWs was estimated. High-density SFs were observed in the scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM) images of the InGaN NWs, and a few zincblende layers appeared in the wurtzite structure. When growth temperature increased, the density of the SFs in the InGaN NW, the photoluminescence (PL) peak wavelength, and the full width at half maximum (FWHM) of PL spectra decreased, whereas the integrated PL intensity increased. These results suggest that a high growth temperature is effective for decreasing the density of SFs in InGaN NWs, and InGaN NWs grown at high temperature have strong PL luminescence due to the low In composition and the corresponding low SFs density.

DOI： 10.7567/JJAP.52.08JE06

Effects of Nano- and Microscale SiO2 Masks on the Growth of a-Plane GaN Layers on r-Plane Sapphire Reviewed

Ji-Su Son, Cao Miao, Yoshio Honda, Masahito Yamaguchi, Hiroshi Amano, Yong Gon Seo, Sung-Min Hwang, and Kwang Hyeon Baik

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JC04 2013.8

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

We report on the combined effects of a-plane GaN layers on a nanoscale patterned insulator on an r-plane sapphire substrate and epitaxial lateral overgrowth (ELOG) techniques. The fully coalescent a-plane GaN layer using nano- and microscale SiO2 masks showed the formation of nano- and microscale voids on the masks, respectively. Atomic force microscopy (AFM) measurements revealed a surface roughness of 0.63 nm and a submicron pit density of 7.8 ×107 cm-2. Photoluminescence (PL) intensity was enhanced by a factor of 9.0 in comparison with that of a planar sample. Omega full-width at half-maximum (FWHM) values of the (1120) X-ray rocking curve along the c- and m-axes were 553 and 788 arcsec, respectively. A plan-view cathodoluminescence (CL) mapping image showed high luminescence intensity on the SiO2 masks.

DOI： 10.7567/JJAP.52.08JC04

High Internal Quantum Efficiency Blue-Green Light-Emitting Diode with Small Efficiency Droop Fabricated on Low Dislocation Density GaN Substrate Reviewed

Tomotaka Sano, Tomohiro Doi, Shunko Albano Inada, Tomohiko Sugiyama, Yoshio Honda, Hiroshi Amano, and Takashi Yoshino

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JK09 2013.8

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

We fabricated blue, blue-green, and green light-emitting diodes (LEDs) of different dislocation densities (DD) and characterized their internal quantum efficiency (IQE). The IQE of the blue LEDs fabricated using GaN substrate exceeded 90 percent, however, when we used a GaN-on-sapphire substrate, IQE was limited to 60 percent. Droop was reduced by use of the GaN substrate. The junction temperature of the GaN-on-sapphire substrate was found to be 200 degreeC although the junction temperature of the GaN substrate was 50 degreeC when a forward current of 100 A/cm2 was driven. A lowering of IQE in green LEDs to 60 percent was observed, even though we used a low-dislocation-density substrate.The junction temperature of blue-green and green LEDs was about 100 degreeC when a forward current of 177 A/cm2 was driven, which indicated that junction temperature is not a major factor for IQE suppression in green LEDs.

DOI： 10.7567/JJAP.52.08JK09

Growth Mode and Threading Dislocation Behavior of GaN Films Grown on Patterned Sapphire Substrate with Radial Stripe Pattern Reviewed

Koji Okuno, Takahide Oshio, Naoki Shibata, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JB09 2013.8

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

A sapphire substrate with a grooved stripe pattern along different radial directions was prepared to investigate the effects of stripe direction on the growth mode and threading dislocation (TD) behavior of GaN films. When the stripe direction is oriented parallel to [1010]sapphire, the GaN films have a triangular structure that is formed by the GaN{1011} facets. As the stripe direction rotates from [1010]sapphire, nanosteps with a step height of around 80 nm are formed on the GaN{1011} facets and then the coalescence of GaN on the ridges and grooves advances. GaN films with a smooth surface and a TD density as low as 2.0×108 cm-2 were achieved when the stripe direction was rotated 3° from [1010]sapphire. Our result indicates that the surface roughness and TD density of GaN films can be controlled by precisely adjusting the angle of the stripe direction from [1010]sapphire.

DOI： 10.7567/JJAP.52.08JB09

Thick InGaN Growth by Metal Organic Vapor Phase Epitaxy with Sputtered InGaN Buffer Layer Reviewed

Toshiya Ohata, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JB11 2013.8

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

A thick InGaN film was grown on a sapphire substrate by metal organic vapor phase epitaxy using a thin buffer layer of sputter-deposited InGaN. A thick film of highly luminescent In0.2Ga0.8N can be successfully grown at a rate as high as 2 µm/h. The crystal quality of InGaN grown on the sputter-deposited InGaN buffer layer was better than that of InGaN grown directly on the sapphire substrate. The sample showed n-type conduction with a carrier concentration and mobility of 5×1018 cm-3 and 3 cm2/(V·s), respectively.

DOI： 10.7567/JJAP.52.08JB11

Combination of ITO and SiO2/AlN Dielectric Multilayer Reflective Electrodes for UV-Emitting Diodes Reviewed

Tsubasa Nakashima, Kenichiro Takeda, Hiroshi Shinzato, Motoaki Iwaya, Satoshi Kamiyama, Tetsuya Takeuchi, Isamu Akasaki, and Hiroshi Amano

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JG07 2013.8

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

We have investigated novel reflective electrodes by combining an ITO layer and a SiO2/AlN dielectric multilayer (DM) for UV-light-emitting diodes (LEDs). The reflectance of 10 pairs of SiO2/AlN DM reached 98.5 percent at 350 nm. As a result, the ITO/DM electrodes simultaneously satisfied the requirements of high reflectivity in the UV region, good contact characteristics, and current spreading. The light output power of the UV LED with an ITO/DM electrode is 1.2 and 1.6 times higher than those of LEDs with ITO/Al and Ni/Au electrodes, respectively.

DOI： 10.7567/JJAP.52.08JG07

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Papers - AMANO, Hiroshi