研究者詳細 - 天野　浩

論文 - 天野　浩

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Low leakage current in AlGaN/GaN HFETs with preflow of Mg source before growth of u-GaN buffer layer 査読有り

Oshimura, Yoshinori; Sugiyama, Takayuki; Takeda, Kenichiro; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi

Physica Status Solidi A 208 巻 ( 7 ) 頁： 1607-1610 2011年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

AlGaN/GaN heterostructure field-effect transistors were grown by metalorg. vapor phase epitaxy on Fe-doped GaN substrates with a preflow of the Mg source. We realized a low drain leakage current, 1.05 μA/mm, at VDS = 20 V and VGS = -5 V with LGD = 3 μm. This leakage current was one order of magnitude lower than that obtained without a preflow of the Mg source. The breakdown voltage was over 250 V with LGD = 10 μm. The on resistance was estd. to be 3.6 mΩ cm2. No significant redistribution or memory effect of Mg was obsd. by secondary ion mass spectroscopy measurement.

Optical properties of (1-101) InGaN/GaN MQW stripe laser structure on Si substrate 査読有り

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

Physica Status Solidi C 8 巻 ( 7-8 ) 頁： 2160-2162 2011年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

A smooth laser structure on (1-101) GaN microstripes was successfully fabricated on a patterned (100) 8°-off Si substrate. The sample has a high internal quantum efficiency (IQE) compared with blue LEDs on a sapphire substrate. The high-d. excitation PL spectrum obsd. from the cross section of the sample shows marked narrowing, and the integral PL intensity also shows a steep increase. These results indicate the onset of stimulated emission from an InGaN-based multi quantum well (MQW) active layer on (1-101) GaN (100) Si. To the best of our knowledge, this is the first report of the observation of a stimulated emission from a (1-101) MQW on a Si substrate. We succeeded in fabricating and verifying the high-quality laser structure on semipolar (1-101) GaN on a Si substrate.

Optimization of initial MOVPE growth of non-polar m- and a-plane GAN on Na flux grown LPE-GaN substrates 査読有り

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 C 8 巻 ( 7-8 ) 頁： 2095-2097 2011年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

We optimized the initial GaN growths of nonpolar m- and a-plane GaN grown on liq. phase epitaxy (LPE-) GaN substrates. Such nonpolar LPE-GaN substrates were produced by cutting slices from c-plane LPE-GaN bulk single crystals grown by the Na-flux method. We investigated the qualities of epitaxially grown GaN layers on the LPE-GaN substrates, with different polishing methods, which are chem. mech. polishing and plasma dry etch polishing. We found that the cryst. quality of epitaxial GaN on m-plane GaN is very sensitive to the surface polishing even the minute unevenness in GaN substrate. Our expts. also indicated that a low initial growth rate was necessary to obtain high-cryst.-quality epitaxial m-plane GaN. In contrast, high-cryst.-quality a-plane GaN was obtained even with a high initial growth rate, indicating that the cryst. quality of a-plane GaN is not sensitive to surface roughness.

Selective MOVPE growth of InGaN/GaN MQW on microfacet GaN stripes 査読有り

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

Physica Status Solidi C 8 巻 ( 7-8 ) 頁： 2038-2040 2011年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

We demonstrated the effects of growth conditions such as growth pressure and growth temp. during the selective growth of InGaN/GaN multiple quantum wells (MQWs) on semipolar GaN microstripes on Si substrates. Grown layers exhibited the ridge growth, which indicates the thickness fluctuation, owing to the source supply from the apexes of the GaN microstructure. Ridge growth was suppressed by increasing growth pressure and decreasing growth temp. Cathode luminescence (CL) anal. showed uniform luminescence. As a result, high pressure and low temp. are suitable for obtaining uniform heterostructures in the selective growth of InGaN/GaN MQWs on GaN microstripes.

Nonpolar a-plane AlGaN/GaN heterostructure field-effect transistors grown on freestanding GaN substrate 査読有り

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

Applied Physics Express ４巻 ( ６ ) 頁： 064102/1-064102/3 2011年6月

記述言語：英語掲載種別：研究論文（学術雑誌）

We fabricated and characterized nonpolar a-plane AlGaN/GaN heterostructure field-effect transistors (HFETs) grown on an a-plane freestanding GaN substrate. By optimizing the growth conditions, the unintentionally doped oxygen concn. was much reduced in the a-plane GaN buffer layer. As a result, the low leakage current in the buffer layer was realized without doping of deep acceptors, such as Fe and C, by which an impurity-contamination-free channel layer can be successfully grown.

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

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

Applied Physics Letters ９８巻 ( ５ ) 頁： 051902/1-051902/3 2011年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

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.

Effect of lateral vapor phase diffusion during the selective growth of InGaN/GaN MQW on semipolar and nonpolar GaN stripes 査読有り

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

Physica Status Solidi A 208 巻 ( 5 ) 頁： 1175-1178 2011年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

We investigated the InGaN/GaN multiple quantum well (MQW) thickness and cathode luminescence (CL) distribution on nonpolar (11-20)GaN, semipolar (11-22)GaN, and (1-101)GaN microstripes grown by selective metal-org. vapor phase epitaxy (MOVPE) on patterned Si substrates. All samples exhibited ridge growth. To clarify the effect of vapor phase diffusion, the two-dimensional diffusion equation was solved. The results were in good agreement with the thickness distribution on the (11-20)GaN stripe when we assumed D/k0 to be 1 μm. However, the results were not in agreement for the semipolar case. On the semipolar face, the surface migration length might be greater, thus increasing the thickness nonuniformity. CL anal. indicated a uniform indium compn. on the (11-20) and (11-22) faces. On the (1-101)GaN stripe, the indium compn. decreased near the (0001) edge. Excess Ga is considered to affect the compositional nonuniformity on the (1-101) facet.

Evidence for moving of threading dislocations during the VPE growth in GaN thin layers 査読有り

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

Physica Status Solidi C 8 巻 ( 5 ) 頁： 1487-1490. 2011年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読有り

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 208 巻 ( 5 ) 頁： 1191-1194 2011年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読有り

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

Applied Physics Express 4 巻 ( 5 ) 頁： 052101/1-052101/3 2011年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読有り

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 8 巻 ( 5 ) 頁： 1467-1470 2011年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

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.

Freestanding highly crystalline single crystal AlN substrates grown by a novel closed sublimation method 査読有り

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

Applied Physics Express 4 巻 ( 4 ) 頁： 045503/1-045503/3 2011年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読有り

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

Applied Physics Letters 98 巻 ( 14 ) 頁： 141905/1-141905/3 2011年3月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読有り

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

Physica Status Solidi RRL: 5 巻 ( 3 ) 頁： 125-127. 2011年3月

記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読有り

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 98 巻 ( 7 ) 頁： 072104/1-072104/3 2011年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読有り

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 4 巻 ( 2 ) 頁： 021001/1-021001/3 2011年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読有り

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 8 巻 ( 2 ) 頁： 464-466 2011年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

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%

Microstructures of GaInN/GaInN superlattices on GaN substrates 査読有り

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

Applied Physics Express 4 巻 ( 1 ) 頁： 015701/1-015701/3. 2011年1月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

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.

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

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

Japanese Journal of Applied Physics 50 巻 ( 1 ) 頁： 01AD04/1-01AD04/3. 2011年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読有り

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

Japanese Journal of Applied Physics 50 巻 ( 1 ) 頁： 01AD03/1-01AD03/3 2011年1月

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