Faculty Profiles - AMANO, Hiroshi

Papers - AMANO, Hiroshi

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Evidence for moving of threading dislocations during the VPE growth in GaN thin layers Reviewed

Kuwano, Noriyuki; Miyake, Hideto; Hiramatsu, Kazumasa; Amano, Hiroshi; Akasaki, Isamu

Physica Status Solidi C Vol. 8 ( 5 ) page： 1487-1490. 2011.5

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

Cross-sectional transmission electron microscope (TEM) observation was performed in detail to analyze the morphol. of threading dislocations (TDs) in GaN thin layers with various thicknesses. The GaN layers were overgrown on an Al0.28Ga0.72N layer by the metal-org. vapor-phase epitaxy (MOVPE) method. In a GaN layer about 50 nm in thickness, TDs running up in the AlGaN layer pass into the GaN layer and most of them reach the top surface without bending. In thicker GaN layers, on the other hand, many of TDs form a hairpin-configuration on or above the interface of GaN and AlGaN to be annihilated. This difference in morphol. of TDs indicates that the TDs have moved down inside the GaN layer. Since the formation of hairpins is attributed to a stress-relief, there should be an extra half-plane between the paired TDs. Therefore, the movement of TDs should be of "climb motion". Another example of possible TD movement inside a GaN layer is also described. It is emphasized that the possibility of TD-movements inside the thin film crystal during the growth should be taken into account in anal. of thin-layer growth through the behavior of TDs.

Growth of AlGaN/GaN heterostructure on vicinal m-plane free-standing GaN substrates prepared by the Na flux method Reviewed

Isobe, Yasuhiro; Iida, Daisuke; Sakakibara, Tatsuyuki; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi; Imade, Mamoru; Kitaoka, Yasuo; et al

Physica Status Solidi A Vol. 208 ( 5 ) page： 1191-1194 2011.5

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

We fabricated and characterized AlGaN/GaN heterostructure growth by MOVPE on vicinal m-plane free-standing GaN substrates prepd. by the Na flux method. The miscut angle in the LPE-GaN substrate has a great influence on the surface morphol. and cryst. quality of epitaxial GaN and AlGaN films. In particular, AlGaN/GaN on a 4° miscut-angle LPE-GaN substrate shows large step bunching, small-miscut-angle LPE GaN substrate is essential for fabricating on FET structure with a flat surface.

Internal quantum efficiency of whole-composition-range AlGaN multiquantum wells Reviewed

Ban, Kazuhito; Yamamoto, Jun-ichi; Takeda, Kenichiro; Ide, Kimiyasu; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi

Applied Physics Express Vol. 4 ( 5 ) page： 052101/1-052101/3 2011.5

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

We analyze the internal quantum efficiency (IQE) of whole-compn.-range AlGaN multiquantum wells (MQWs) on AlGaN with various dislocation densities (DDs) by excitation-d.-dependent photoluminescence measurement. IQEs of deep UV/UV (DUV/UV) MQWs are strongly dependent on the DD. IQE with an excess carrier d. of 1 × 1018 cm-3 changes from 4 to 64% when the DD changes from 6 × 109 to 2 × 108 cm-2. This trend is almost the same for DUV/UV MQWs with emission wavelength ranging from 230 to 350 nm. Thus, the redn. of the DD is very important for the realization of a high-IQE DUV/UV active layer.

Microstructural analysis of thick AlGaN epilayers using Mg-doped AlN underlying layer Reviewed

Nonaka, K.; Asai, T.; Ban, K.; Yamamoto, J.; Iwaya, M.; Takeuchi, T.; Kamiyama, S.; Akasaki, I.; Amano, H.; Wu, Z. H.

Physica Status Solidi C Vol. 8 ( 5 ) page： 1467-1470 2011.5

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

This paper reports the microstructural anal. of 20-μm-thick Al0.5Ga0.5N with improved cryst. quality owing to the use of a Mg-doped AlN underlying layer. The threading dislocation d. in 20-μm-thick Al0.5Ga0.5N on Mg-doped AlN was 8.6 × 108 cm-2, which is about one-fifth lower than that of Al0.5Ga0.5N on an undoped AlN underlying layer. The microstructural anal. was carried out to clarify dislocation behaviors in the Al0.5Ga0.5N layer on the Mg-doped AlN underlying layer.

Partial strain relaxation by stacking fault generation in InGaN multiple quantum wells grown on (1-101) semipolar GaN Reviewed

Wu, Z. H.; Tanikawa, T.; Murase, T.; Fang, Y.-Y.; Chen, C. Q.; Honda, Y.; Yamaguchi, M.; Amano, H.; Sawaki, N.

Applied Physics Letters Vol. ９８ ( ５ ) page： 051902/1-051902/3 2011.5

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

The authors have studied the structural properties and relaxation phenomenon of InGaN multiple quantum wells (QWs) on (1.hivin.101) semipolar GaN templates grown on patterned (001) Si substrates by selective area growth technique. Studies by TEM and x-ray diffraction reciprocal space mapping reveal that QWs emitting light at 540 nm experience significant strain relaxation along the in-plane [1.hivin.10.hivin.2] direction by the generation of an array of basal stacking faults (BSF). The generation of BSFs in 540 nm QWs could be an important factor limiting its luminescence efficiency.

Freestanding highly crystalline single crystal AlN substrates grown by a novel closed sublimation method Reviewed

Yamakawa, Masayasu; Murata, Kazuki; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi; Azuma, Masanobu

Applied Physics Express Vol. 4 ( 4 ) page： 045503/1-045503/3 2011.4

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

We fabricated thick freestanding AlN films by a novel close-spaced sublimation method. The spacing between a sintered AlN polycrystal and a SiC substrate is 1 mm. A Ta ring was used to control the spacing between the AlN polycrystal and the SiC substrate. In addn., a special AlN adhesive was also used to fill in the gap between the AlN polycrystal, the Ta ring, and the SiC substrate. By a combination of these techniques, an AlN growth rate as high as 600 μm/h was achieved. A freestanding AlN layer was obtained by the sublimation of the SiC substrate during the AlN growth.

Spontaneous formation of highly regular superlattice structure in InGaN epilayers grown by molecular beam epitaxy Reviewed

Wu, Z. H.; Kawai, Y.; Fang, Y.-Y.; Chen, C. Q.; Kondo, H.; Hori, M.; Honda, Y.; Yamaguchi, M.; Amano, H.

Applied Physics Letters Vol. 98 ( 14 ) page： 141905/1-141905/3 2011.3

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

Structural properties of thick InGaN layers grown on GaN by plasma-assisted mol. beam epitaxy using two growth rates of 1.0 and 3.6 Å/s have been investigated. A highly regular superlattice (SL) structure formed spontaneously in the film grown at 3.6 Å/s but not in the film grown at 1.0 Å/s. The faster grown film also exhibited superior structural quality, which could be due to the surface roughness suppression caused by kinetic limitation, and the inhibition of the Frank-Read dislocation generation mechanism within the spontaneously formed SL structure.

Demonstration of diamond field effect transistors by AlN/diamond heterostructure Reviewed

Imura, Masataka; Hayakawa, Ryoma; Watanabe, Ei-Ichiro; Liao, Mei-Yong; Koide, Yasuo; Amano, Hiroshi

Physica Status Solidi RRL: Vol. 5 ( 3 ) page： 125-127. 2011.3

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

This is the first report on an AlN/diamond heterojunction field effect transistor (HFET). The AlN epilayer is grown on oxygen-terminated (111) diamond substrates using metalorg. vapor phase epitaxy at a temp. as high as 1240 °C. The transistor and gate capacitance-voltage characteristics indicate that the HFET behaves as a p-channel FET with a normally-on depletion mode. The HFET channel is located at the AlN/diamond interface, and holes are accumulated in diamond close to the interface. The development of the AlN/diamond HFET creates a new possibility for diamond-based power electronics.

Role of nonradiative recombination centers and extended defects in nonpolar GaN on light emission efficiency Reviewed

Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Amano, H.; Pearton, S. J.; Lee, I.-H.; Sun, Q.; Han, J.; Karpov, S. Yu.

Applied Physics Letters Vol. 98 ( 7 ) page： 072104/1-072104/3 2011.2

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

The correlation of integrated microcathodoluminescence efficiency with cryst. quality and deep trap d. of nonpolar GaN films grown by metal org. CVD on semi-insulating 6H-m-SiC or r-sapphire is analyzed. The results suggest a strong influence of nonradiative recombination centers whose concn. decreases with decreased d. of extended defects. Electron traps with energy levels at Ec-0.6 eV and which pin the Fermi level in films with high defect d. are the most likely candidates for the decrease in light emission efficiency in nonpolar GaN.

GaInN-based solar cells using strained-layer GaInN/GaInN superlattice active layer on a freestanding GaN substrate Reviewed

Kuwahara, Yousuke; Fujii, Takahiro; Sugiyama, Toru; Iida, Daisuke; Isobe, Yasuhiro; Fujiyama, Yasuharu; Morita, Yoshiki; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi, Amano Hiroshi; et al

Applied Physics Express Vol. 4 ( 2 ) page： 021001/1-021001/3 2011.2

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

High-performance GaInN-based solar cells with high open-circuit voltage, high short-circuit c.d., and good fill factor have been obtained using a combination of two different GaInN superlattice structures. The GaInN barrier thicknesses (3 and 0.6 nm) in both superlattice structures were optimized, resulting in a thick GaInN-based active layer with a low pit d. in the device. The conversion efficiency is 2.5% under a solar simulator of air-mass 1.5G and an irradn. intensity of 155 mW/cm2.

Internal quantum efficiency and internal loss of ultraviolet laser diodes on the low dislocation density AlGaN underlying layer Reviewed

Takeda, Kenichiro; Nagata, Kengo; Ichikawa, Tomoki; Nonaka, Kentaro; Ogiso, Yuji; Oshimura, Yoshinori; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; et al

Physica Status Solidi C Vol. 8 ( 2 ) page： 464-466 2011.2

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

We fabricated and evaluated GaN/AlGaN multi-quantum wells (MQWs) and UV laser diodes (UV LDs) on high and low dislocation d. underlying layers by epitaxial lateral overgrowth (ELO) method. We analyzed the internal quantum efficiency (IQE) vs. carrier concn. characteristics quant. by excitation intensity dependent photoluminescence method. The IQE of the MQWs on the ELO AlGaN is 75% when the carrier d. is 1 × 1019 cm-3. We demonstrated the UV LD on the ELO AlGaN. However, the UV LD on flat AlGaN did not operate. Also, we investigated the internal loss (α1) and the IQE multiplied the injection efficiency by changing the reflectivity of the facets. The results showed that the internal loss is 6 cm-1, and the IQE multiplied by the injection efficiency is 18%

Drastic reduction of dislocation density in semipolar (11-.22) GaN stripe crystal on Si substrate by dual selective metal-organic vapor phase epitaxy Reviewed

Murase, Tasuku; Tanikawa, Tomoyuki; Honda, Yoshio; Yamaguchi, Masahito; Amano, Hiroshi; Sawaki, Nobuhiko

Japanese Journal of Applied Physics Vol. 50 ( 1 ) page： 01AD04/1-01AD04/3. 2011.1

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

A drastic redn. of the dislocation d. in a semipolar (11.hivin.22) GaN stripe on a patterned Si substrate was achieved by the 2-step selective growth of a GaN stripe. After depositing a SiO2 mask on the (11.hivin.22) and (000.hivin.1) faces of a GaN stripe grown on a (113) Si substrate, GaN was regrown only on the (.hivin.1.hivin.122) face. The dislocation d. estd. from the dark-spot d. in a cathodoluminescence (CL) image greatly decreased from 4.0 × 108 to 1.0 × 105/cm2 in the regrowth region. A TEM image also verified that there were no dislocations at the regrowth interfaces.

High-temperature operation of normally off-mode AlGaN/GaN heterostructure field-effect transistors with p-GaN gate Reviewed

Sugiyama, Takayuki; Amano, Hiroshi; Iida, Daisuke; Iwaya, Motoaki; Kamiyama, Satoshi; Akasaki, Isamu

Japanese Journal of Applied Physics Vol. 50 ( 1 ) page： 01AD03/1-01AD03/3 2011.1

MBE-VLS growth of catalyst-free III-V axial heterostructure nanowires on (1 1 1)Si substrates Reviewed

Paek, Jihyun; Yamaguchi, Masahito; Amano, Hiroshi

Journal of Crystal Growth Vol. 323 ( 1 ) page： 315-318 2011.1

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

For application in novel opto-electronic nanowire devices, Ga-assisted GaAs/InxGa1-xAs axial heterostructure nanowires grown on a (1 1 1)Si substrate at a high In/Ga flux ratio were investigated. The increased diam. of the InxGa1-xAs region of the nanowire was obsd. from a SEM image. The In compn. of 0.01-0.02 of the InxGa1-xAs was shown by EDX point anal. The In concn. of 0.62 of an In-Ga alloy droplet was estd. from the diam. ratio of the InxGa1-xAs/GaAs region. From these results, it was considered that the excess In was collected in the droplet, resulting in an increased nanowire diam. The increased diam. of the InxGa1-xAs region was also discussed together with the results of thermodn. calcn.

Microstructures of GaInN/GaInN superlattices on GaN substrates Reviewed

Sugiyama, Toru; Kuwahara, Yosuke; Isobe, Yasuhiro; Fujii, Takahiro; Nonaka, Kentaro; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi

Applied Physics Express Vol. 4 ( 1 ) page： 015701/1-015701/3. 2011.1

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

We found different behaviors of misfit dislocations in a Ga0.83In0.17N single layer and in Ga0.83In0.17N/Ga0.93In0.07N superlattices, both on GaN substrates. In the case of the single layer, misfit dislocations were formed at the GaInN/GaN interfaces and extended through the GaInN layer to the surface. In contrast, the misfit dislocations in the superlattices are bent laterally at interfaces between the Ga0.83In0.17N and Ga0.93In0.07N layers. In addn., most of the dislocations do not reach the surface owing to the formation of dislocation loops. As a result, the dislocation d. at the surface of the GaInN superlattice sample was 5 × 107 cm-2.

Realization of nitride-based solar cell on freestanding GaN substrate Reviewed

Kuwahara, Yosuke; Fujii, Takahiro; Fujiyama, Yasuharu; Sugiyama, Tohru; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi

Applied Physics Express Vol. 3 ( 11 ) page： 111001/1-111001/3 2010.11

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

A p-i-n solar cell composed of an undoped GaInN layer sandwiched between n- and p-type GaN layers was grown on a freestanding c-plane GaN substrate and a c-plane sapphire substrate covered with a low-temp.-deposited buffer layer. The open-circuit voltage is 2.23 V, the fill factor is 61%, the short-circuit c.d. is 1.59 mA/cm2, and the conversion efficiency of the solar cell on the GaN substrate is 1.41% using a solar simulator (1.5 suns). Compared with the solar cell characteristics of the device grown on the sapphire substrate, pit d. markedly decreases. As a result, shunt resistance increases, suppressing the open-circuit voltage drop.

Strain relaxation mechanisms in AlGaN epitaxy on AlN templates Reviewed

Wu, Zhihao; Nonaka, Kentaro; Kawal, Yohjiro; Asai, Toshiaki; Ponce, Fernando A.; Chen, Changqing; Iwaya, Motoaki; Kamiyama, Satoshi; Amano, Hiroshi; Akasaki, Isamu

Applied Physics Express Vol. 3 ( 11 ) page： 111003/1-111003/3 2010.11

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

Two strain relaxation processes have been obsd. in AGaN layers grown on thick AlN templates. In Process I, a type threading dislocations (TDs) with b = 1/3.ltbbrac.11.hivin.20.rtbbrac. from the AlN underlayer are inclined away from the [0001] axis toward the .ltbbrac.1.hivin.100.rtbbrac. directions when they enter the AlGaN film, forming dislocation line projection perpendicular to the Burger vector. In Process II, a + c-type TDs from the AlN underlayer with Burgers vector of b = 1/3.ltbbrac.11.hivin.23.rtbbrac. glide on {0.hivin.111} planes when they enter the AlGaN film to generate interfacial misfit dislocations lying along the .ltbbrac..hivin.2110.rtbbrac. directions at the AlGaN/AlN interface.

Analysis of polar direction of AlN grown on (0001) sapphire and 6H-SiC substrates by high-temperature metal-organic vapor phase epitaxy using coaxial impact collision ion scattering spectroscopy Reviewed

Imura, Masataka; Ohnishi, Tsuyoshi; Sumiya, Masatomo; Liao, Meiyong; Koide, Yasuo; Amano, Hiroshi; Lippmaa, Mikk

Physica Status Solidi C Vol. 7 ( 10 ) page： 2365-2367 2010.10

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

High-cryst. quality AlN layers with an atomically flat surface are grown on (0001) sapphire and 6H-SiC substrates by metal-org. vapor phase epitaxy at 1400 °C without low-temp. buffer layer. The polar direction of AlN layers is investigated by coaxial impact-collision ion scattering spectroscopy (CAICISS). For AlN growth on sapphire substrate, trimethylaluminum (TMAI) is supplied for 10 s before introducing ammonia (NH3). For AlN growth on SiC substrate, TMAl and NH3 are supplied at the same time. The CAICISS spectrum of AlN layers is analyzed by measuring the dependence of the Al atoms signal intensity on the angle of ion beam incidence considering the shadowing and focusing effects for detg. the polar direction of AlN layers. The CAICISS spectra clearly indicate the polar direction of AlN layers and both AlN layers are found to be had the Al-polarity.

Atomic layer epitaxy of AlGaN Reviewed

Nagamatsu, Kentaro; Iida, Daisuke; Takeda, Kenichiro; Nagata, Kensuke; Asai, Toshiaki; Iwaya, Motoaki; Kamiyama, Satoshi; Amano, Hiroshi; Akasaki, Isamu

Physica Status Solidi C: Vol. 7 ( 10 ) page： 2368-2370 2010.10

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

Atomic layer epitaxy of AlGaN with an av. growth rate of as high as 4.5 mm/h has been achieved by the high-speed switching-valves (HSSVs) technique in a raised-pressure metalorg. vapor phase epitaxy system. Regarding the duration of group III metalorgs. and NH3 gases input, 0.1 s for each injection time is found to be sufficient to realize AlGaN growth of one monolayer per cycle over a 2-in. wafer with hydrogen and nitrogen carrier gases at a raised pressure. Low-temp. growth of high-quality AlGaN has been achieved using HSSVs.

GaInN/GaN p-i-n light-emitting solar cells Reviewed

Fujiyama, Y.; Kuwahara, Y.; Iwaya, M.; Kamiyama, S.; Amano, H.; Akasaki, I.

Physica Status Solidi C Vol. 7 ( 10 ) page： 2382-2385. 2010.10

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

GaInN/GaN p-i-n double-heterojunction structures were grown by metal-org. vapor phase epitaxy on c-plane sapphire substrates, and light-emitting solar cells with different GaInN active layer thicknesses were fabricated. The thickness of the GaInN active layer was varied from 100 to 400 nm, while the thickness of both n-type and p-type GaN layers was kept const. A semitransparent ohmic contact to p-type GaN was formed by electron-beam evapn. of Ni/Au (5 nm/5 nm). The film thickness of p-GaN was 50 nm. The external quantum efficiency (EQE) of the device with a 400 nm GaInN layer exceeded 60% at a wavelength of approx. 380 nm. The transparency of the Ni/Au electrode was 68%. Therefore, the internal quantum efficiency of this device exceeded 95%. Note that this device emitted green light when a forward voltage was applied. The electroluminescence peak wavelength was approx. 525 nm, which was much longer than the EQE peak wavelength. The origin of this large emission shift is discussed.

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Papers - AMANO, Hiroshi