Faculty Profiles - AMANO, Hiroshi

Papers - AMANO, Hiroshi

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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 Open Access

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

Progress and Prospect of the Growth of Wide-Band-Gap Group III Nitrides: Development of the Growth Method for Single-Crystal Bulk GaN Reviewed

Hiroshi Amano

Japanese journal of applied physics Vol. 52 ( 5 ) page： 050001-1-050001-10 2013.5

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

With the continuously increasing demand for the conservation and generation of energy, bulk substrates of group III nitride semiconductors are highly expected to maximize their potential. In this report, I review the current status of the growth methods for bulk GaN single crystals used for substrates as well as summarize the characteristics of blue light-emitting diodes (LEDs), heterojunction field-effect transistors (HFETs), and photovoltaic cells on GaN substrates.

DOI： 10.7567/JJAP.52.050001

AlN/air distributed Bragg reflector by GaN sublimation from microcracks of AlN Reviewed

T. Mitsunari, T. Tanikawa, Y. Honda, M. Yamaguchi, H. Amano

Journal of Crystal Growth Vol. 370 ( 1 ) page： 16-21 2013.5

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

The GaN/AlN multilayer structure was grown on a stripe-patterned and dot-patterned Si substrate, and subsequently annealed at 1200 °C in H2 and NH3 atmosphere. We achieved an AlN/air structure by the decomposition of GaN from the microcracks of AlN. Partially crack-free AlN layers were observed over a 5×5 μm area in the c-plane of AlN/air DBRs.

DOI： 10.1016/j.jcrysgro.2012.09.062

Structural evolution of AlN buffer and crystal quality of GaN films on a- and c-sapphire grown by metalorganic vapor phase epitaxy Reviewed

Okuno, Koji; Oshio, Takahide; Shibata, Naoki; Honda, Yoshio; Yamaguchi, Masahito; Tanaka, Shigeyasu; Amano, Hiroshi

Physica Status Solidi C Vol. 10 ( 3 ) page： 369-372 2013.3

Effects of low energy e-beam irradiation on cathodoluminescence from GaN Reviewed

Suihkonen, S.; Nykaenen, H.; Tanikawa, T.; Yamaguchi, M.; Honda, Y.; Amano, H.

Physica Status Solidi A Vol. 210 ( 2 ) page： 383-385 2013.2

Development of High-Density Nitrogen Radical Source for Low Mosaicity and High Rate Growth of InGaN Films in Molecular Beam Epitaxy Reviewed

Chen, S ; Kawai, Y ; Kondo, H ; Ishikawa, K ; Takeda, K ; Kano, H ; Sekine, M ; Amano, H Hori, M

Japanese Journal of Applied Physics Vol. 52 ( 2 ) page： 021001-021006 2013.2

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

A high-density radical source (HDRS) was developed by optimizing the antenna structure and introducing an external magnetic field to plasma. Nitrogen radical generation by the HDRS at a density of 2.3 ×1012 atoms cm-3, which was one order higher than that for the conventional radical source (CRS), was achieved. The HDRS- and CRS-assisted InGaN growth in molecular beam epitaxy (MBE) was carried out. For the HDRS case, a diffraction peak in the X-ray rocking curve of the grown InGaN films showed a narrower peak, which width below 600 arcsec even with a high growth rate of 1.4 µm/h for InGaN. MBE with the assistance of HDRS has a great potential in the growth of nitride films with a lower mosaicity and a higher growth rate.

DOI： 10.7567/JJAP.52.021001

Surface potential effect on excitons in AlGaN/GaN quantum well structures Reviewed

Pozina, G.; Hemmingsson, C.; Amano, H.; Monemar, B.

Applied Physics Letters Vol. 102 ( 8 ) page： 082110/1-082110/4 2013.2

Individual roles of atoms and ions during hydrogen plasma passivation of surface defects on GaN created by plasma etching Reviewed

Chen, Shang; Ishikawa, Kenji; Lu, Yi; Kometani, Ryosuke; Kondo, Hiroki; Tokuda, Yutaka; Egawa, Takashi; Amano, Hiiroshi; Sekine, Amano; Hori, Masaru

Japanese Journal of Applied Physics Vol. 51 ( 11 ) page： 111002/1-11102/5 2012.11

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

In the recovery of photoluminescence intensities for band-edge emissions at around 3.47 eV in the case of gallium nitride (GaN), we have studied the individual roles of hydrogen atoms (H) and hydrogen ions (H-n(+)). Surface defects such as nitrogen vacancies created by plasma etching were passivated by H termination. By utilizing hydrogen plasmas, we clarified the recovery efficiency by optical and stoichiometrical improvements with respect to the balance between the fluxes of H and H-n(+). By deflecting H-n(+) by applying an electric field, the efficiency was improved using an identical H dosage, since the simultaneous irradiation of the energetic H-n(+) promoted the desorption of the formed passivated Ga-H bonds.

DOI： 10.1143/JJAP.51.111002

Correlation between device performance and defects in GaInN-based solar cells Reviewed

Mori, Mikiko; Kondo, Shinichiro; Yamamoto, Shota; Nakao, Tatsuro; Fujii, Takahiro; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi

Applied Physics Express Vol. 5 ( 8 ) page： 082301/1-082301/3 2012.8

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

We investigated the correlation between the device performance and defects, such as V-shaped pits and threading dislocations, in GaInN-based solar cells. To realize high-performance GaInN-based solar cells with a high open-circuit voltage and fill factor, it is essential to realize a low pit density of less than 10(7) cm(-2). In this study, we were unable to observe clear evidence of any effect of the threading dislocation density in the GaN underlying layer.

DOI： 10.1143/APEX.5.082301

MOVPE growth of nonpolar a-plane GaN with low oxygen contamination and specular surface on a freestanding GaN substrate Reviewed

Yasuhiro Isobe, Hiromichi Ikki, Tatsuyuki Sakakibara, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki,Takayuki Sugiyama, Hiroshi Amano, Mamoru Imade, Yusuke Mori

Journal of Crystal Growth Vol. 351 ( 1 ) page： 126-130 2012.7

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

We investigated unintentionally doped nonpolar a- and m-plane GaN layers grown by metalorganic vapor phase epitaxy under several sets of conditions on freestanding a- and m-plane GaN substrates. Oxygen contamination in a-plane GaN is greatly reduced by increasing the V/III ratio during growth. As a result, a high-resistivity GaN buffer layer for an AlGaN/GaN heterostructure field-effect transistor was realized.

DOI： 10.1016/j.jcrysgro.2012.04.030

In-situ void formation technique using an AlN shell structure grown on GaN stripes on Si(111) and c-plane sapphire substrates Reviewed

Mitsunari, Tadashi; Tanikawa, Tomoyuki; Honda, Yoshio; Yamaguchi, Masahito; Amano, Hiroshi

Physca Status Solidi c Vol. 9 ( 3-4 ) page： 480-483 2012.7

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

We proposed an in-situ void formation technique using high-temp. AlN growth on GaN stripes in order to reduce residual stress. Microcracks were obsd. during the growth of AlN; the GaN stripes then sublimated from the microcracks while keeping the AlN shell, resulting in void formation in the AlN shell structure. After GaN regrowth on this AlN shell structure, we successfully coalesced the GaN stripes to form a smooth, thick GaN layer having voids at the GaN/substrate interface. Raman spectroscopy confirmed that the residual tensile stress was decreased. The thermal stress decreased owing to the sepn. between the GaN layer and a foreign substrate.

DOI： 10.1002/pssc.201100502

Small current collapse in AlGaN/GaN HFETs on a-plane GaN self-standing substrate Reviewed

T. Sugiyama, Y. Honda, M. Yamaguchi, H. Amano, Y. Isobe, M. Iwaya, T. Takeuchi, S. Kamiyama, I. Akasaki, M. Imade, Y. Kitaoka, Y. Mori

Physica Status Solidi c Vol. 9 ( 3-4 ) page： 875-878 2012.7

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

We measured drain bias stress effects and current collapse in AlGaN/ GaN heterostructure field-effect transistors (HFETs) on a-plane and c-plane GaN substrates. An a-plane AlGaN/GaN HFET (a-HFET) shows small current collapse with a threshold voltage (Vth = -1.8 V). On the other hand, a c-plane HFET (c-HFET) with the same barrier thickness (20 nm) shows a small current collapse, although Vth was neg. large (Vth = -4 V). Current collapse in a-HFET was not large compared with that in conventional c-HFET on GaN. A c-HFET on sapphire was also measured. The current collapses in HFETs on sapphire were larger than that in HFETs on a GaN substrate. The current collapses in the thin-barrier c-HFET (Vth = -1.8 V) were particularly large. Therefore, an a-plane device is promising for a small or pos. Vth with small current collapse.

DOI： 10.1002/pssc.201100397

Laser lift-off of AlN/sapphire for UV light-emitting diodes Reviewed

Aoshima, Hiroki; Takeda, Kenichiro; Takehara, Kosuke; Ito, Shun; Mori, Mikiko; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi

Physica Status Solidi C Vol. 9 ( 3-4 ) page： 753-756 2012.7

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

We report on laser lift-off (LLO) of AlN/sapphire for UV light-emitting diodes (LEDs). Underfill between chip and submount is a key factor for the successful LLO of AlN/sapphire. We fabricated thin-film-flip-chip UV LEDs with a peak wavelength of 343 nm using the LLO. Moreover surface texturing was carried out on the exfoliated AlN surface. The light output power from the UV LED after the LLO and the surface texture at exfoliated surface is 1.7 times higher than that before the LLO at 20 mA.

DOI： 10.1002/pssc.201100491

Growth of InGaN nanowires on a (111)Si substrate by RF-MBE Reviewed

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

Physica Status Solidi c Vol. 9 ( 3-4 ) page： 646-649 2012.7

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

We have grown InGaN nanowires (NWs) on a (111)Si substrate directly by radio-frequency plasma-assisted mol. beam epitaxy (RF-MBE), and investigated their In compositional distribution by energy dispersive x-ray spectroscopy (EDX). The In compn. line profiles of InGaN NWs measured by EDX are different at each position in the InGaN NWs, and In is most easily incorporated into the top of NWs. The In compn. at the top of the NWs depends on the growth temp. and the In flux ratio. However, the In compns. at other positions is not dependent on these factors. Thus, these results might be due to the limited diffusion of In atoms from the top of the NWs towards the NWs/Si interface.

DOI： 10.1002/pssc.201100446

Fabrication of AlInN/AlN/GaInN/GaN heterostructure field-effect transistors Reviewed

Kazuya Ikeda, Yasuhiro Isobe, Hiromichi Ikki, Tatsuyuki Sakakibara, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki, Hiroshi Amano

Physica Status Solidi c Vol. 9 ( 3-4 ) page： 942-944 2012.7

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

We report on the electrical properties of AlInN/GaInN
heterostructures fabricated with InN molar fractions of 0 to 0.6 in the GaInN layer. High-density two-dimensional electron gases are formed near the interfaces of AlInN/AlN/GaInN at InN molar fractions of 0.3 and 0.6.
The Al0.82In0.18N/AlN/Ga0.4In0.6N/GaN heterostructure
field-effect transistors exhibited static characteristics.
The maximum drain-source current reached a value of
0.26 A/mm.

DOI： 10.1002/pssc.201100492

High carrier concentration in high Al-composition AlGaN-channel HEMTs Reviewed

Hashimoto, Shin; Akita, Katsushi; Yamamoto, Yoshiyuki; Ueno, Masaki; Nakamura, Takao; Yafune, Norimasa; Sakuno, Keiichi; Tokuda, Hirokuni; Kuzuhara, Masaaki; Takeda, Kenichiro; Iwaya, Motoaki; Amano, Hiroshi

Vol. 9 ( 2 ) page： 373-376 2012.6

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

High Al-compn. (Al = 51%) and low Al-compn. (Al = 20%) AlGaN-channel high-electron-mobility transistors (HEMTs) on AlN layers with very high carrier concn. were demonstrated. In two types of HEMTs, 2-dimensional electron gases (2DEG) were clearly obsd. and peak carrier concn. and sheet carrier concn. were approx. 1020 cm-3 and higher than 2 × 1013 cm-2, resp. From the X-ray diffraction (XRD) measurements, it was obsd. that the AlGaN channel layers on the AlN layers were partially relaxed and the degree of relaxation decreased with increasing Al-compn. of AlGaN channel layers. Therefore the misfit dislocations in the high Al-compn. HEMTs were considered to be lower than those in the low Al-compn. HEMTs. Furthermore, it was revealed that very high Al-compn. of AlGaN barrier layers can be grown coherently on the AlGaN channel layers in consequence of the partly relaxation of the AlGaN channel layers, which of lattice consts. of a-axis were smaller than that of fully relaxed AlGaN channel layers. Therefore very high carrier concn. of 2DEG can be obtained in spite of the high Al-compn. of AlGaN channel layers. We considered that this high carrier concn. of 2DEG was necessary to demonstrate high Al-compn. AlGaN-channel HEMTs.

DOI： 10.1002/pssc.201100289

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Papers - AMANO, Hiroshi