Faculty Profiles - AMANO, Hiroshi

Papers - AMANO, Hiroshi

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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

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

GaN Nanowires Grown on a Graphite Substrate by Radio Frequency Molecular Beam Epitaxy Reviewed

Shinta Nakagawa, Takuya Tabata, Yoshio Honda, Masahito Yamaguchi, and Hiroshi Amano

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JE07 2013.8

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

Self-assembled GaN and InGaN nanowires (NWs) were directly grown on a highly oriented pyrolytic graphite (HOPG) substrate by radio frequency molecular beam epitaxy (RF-MBE). The GaN NWs grown on HOPG had a shorter length and larger diameter than those grown conventionally on a Si(111) substrate based on the analysis of scanning electron microscopy (SEM) images. They were also found to have good crystalline qualities with few stacking faults, as determined by scanning transmission electron microscopy (STEM) analysis. Photoluminescence (PL) measurements at room temperature indicated that the luminescence intensity of the GaN NWs on HOPG is stronger than that of NWs grown on a Si(111) substrate; however, the InGaN NWs on both substrates showed similar tendencies with respect to the shift of the luminescence wavelength as a function of the growth temperature. While In incorporation decreased as the growth temperature increased, the uniformity of the InGaN NW arrays improved rapidly.

DOI： 10.7567/JJAP.52.08JE07

Concentrating Properties of Nitride-Based Solar Cells Using Different Electrodes Reviewed

Mikiko Mori, Shinichiro Kondo, Shota Yamamoto, Tatsuro Nakao1, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki, and Hiroshi Amano

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JH02 2013.8

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

We investigated the concentration properties of GaInN-based solar cells using different window electrodes. A significant difference was observed between the concentrating properties of the window electrode structures. It was clearly found that indium tin oxide (ITO) is suitable as an electrode. The short-circuit current density, open-circuit voltage, fill factor, and energy conversion efficiency of nitride-based solar cells fabricated using an ITO electrode were 7.1×102 mA/cm2, 2.2 V, 79%, and 4.0%, respectively, under an air mass filter of 1.5G at 300 suns and at room temperature.

DOI： 10.7567/JJAP.52.08JH02

Emission Wavelength Dependence of Internal Quantum Efficiency in InGaN Nanowires Reviewed

Hideaki Murotani, Hiroya Andoh, Takehiko Tsukamoto, Toko Sugiura, Yoichi Yamada, Takuya Tabata, Yoshio Honda, Masatoshi Yamaguchi, and Hiroshi Amano

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JE10 2013.8

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

The internal quantum efficiency (IQE) of InGaN nanowires with different emission wavelength of 485, 515, 555, and 580 nm has been studied by means of photoluminescence (PL) spectroscopy. It was found from the analysis of IQE as a function of excitation power density that the IQE was unchanged at about 100% under weak excitation conditions at low temperature. This indicated that the effects of nonradiative recombination processes were negligibly small at low temperature. Moreover, the IQE increased from 5 to 12% with increasing emission wavelength from 485 to 580 nm. Since the clear correlation between the IQE and the PL blue shift due to band filling effects of localized states was observed, the increase in the IQE reflected the increase in the effect of exciton localization with increasing indium composition.

DOI： 10.7567/JJAP.52.08JE10

Luminescence of Acceptors in Mg-Doped GaN Reviewed

Bo Monemar, Sergey Khromov, Galia Pozina, Plamen Paskov, Peder Bergman, Carl Hemmingsson, Lars Hultman, Hiroshi Amano, Vitaliy Avrutin, Xing Li, and Hadis Morkoç

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JJ03 2013.8

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

It is concluded that the typical PL peaks at 3.466 eV (ABE1)and the broader 3.27 eV DAP PL are the expected standard PL signatures of the substitutional Mg acceptor. Additional broader peaks at 3.455 eV (ABE2) and 3.1 eV are suggested to be related to the same acceptors perturbed by nearby basal plane stacking faults. The low temperature metastability of PL spectra is assigned to a nonradiative metastable deep level.

DOI： 10.7567/JJAP.52.08JJ03

Analysis of Broken Symmetry in Convergent-Beam Electron Diffraction along <11-20 > and <1-100 > Zone-Axes of AlN for Polarity Determination Reviewed

Masataka Imura, Ujjal Gautam, Kiyomi Nakajima, Yasuo Koide, Hiroshi Amano, and Kenji Tsuda

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JE15 2013.8

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

To accurately and easily determine the polarity of AlN using transmission electron microscopy, we compare the convergent-beam electron diffraction (CBED) patterns along the widely used <1120 > and <1100 > zone-axes. For the <1120 > zone-axis, the diffraction disk of g= 0002 differs from that of g= 0002, while for <1100 >, the diffraction disks of g= 0002 and 0002 are similar. The preferential clarity of these two disks is explained using Bloch-wave dynamical theory. To further support the explanation, we compare the results of GaN case. On the basis of our analysis, we conclude that the CBED patterns of the <1120 > zone-axis are more useful for accurately determining AlN polarity compared to the CBED patterns along the <1100 > zone-axis.

DOI： 10.7567/JJAP.52.08JE15

Microstructure Analysis of AlGaN on AlN Underlying Layers with Different Threading Dislocation Densities Reviewed

Kimiyasu Ide, Yuko Matsubara, Motoaki Iwaya, Satoshi Kamiyama, Tetsuya Takeuchi, Isamu Akasaki, and Hiroshi Amano

Jpn. J. Appl. Phys. Vol. 52 ( 8 ) page： 08JE22 2013.8

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

Using the epitaxial lateral growth technique, we compared the crystallinity and relaxation ratio of 3-µm- and 200-nm-thick Al0.5Ga0.5N on an AlN template and AlN grown by epitaxial lateral overgrowth (ELO-AlN), both of which were grown on a sapphire substrate. Although the relaxation ratios of 3-µm-thick Al0.5Ga0.5N were almost the same, the misfit dislocation density at the interface and the density of threading dislocations reaching the surface of Al0.5Ga0.5N were significantly different. Also, the increase in the density of newly generated misfit dislocations was found to be highly dependent on the quality of the AlN underlying layer. We also discuss the difference in the initial growth mode of each Al0.5Ga0.5N sample.

DOI： 10.7567/JJAP.52.08JE22

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

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

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Papers - AMANO, Hiroshi