Faculty Profiles - AMANO, Hiroshi

Papers - AMANO, Hiroshi

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Temperature dependence of normally off mode AlGaN/GaN heterostructure field-effect transistors with p-GaN gate Reviewed

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

Physica Status Solidi C: Vol. 7 ( 10 ) page： 2419-2422 2010.10

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

We demonstrated high-temp. operation of normally off-mode junction-heterostructure-field-effect transistors (JHFETs) with a p-GaN gate that shows a very small shift of the threshold voltage against ambient temp. Distinct normally off-mode operation with a max. drain current of 93.2 mA/mm at 300 °C was realized. Therefore, normally off-mode GaN-based JFETs are greatly superior to Si-based devices as high-temp. switching devices.

Threshold voltage control using SiNx in normally off AlGaN/GaN HFET with p-GaN gate Reviewed

Sugiyama, T.; Iida, D.; Iwaya, M.; Kamiyama, S.; Amano, H.; Akasaki, I.

Physica Status Solidi C Vol. 7 ( 7-8 ) page： 1980-1982 2010.7

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

The threshold voltage (Vth) of normally off-mode AlGaN/GaN junction heterostructure field-effect transistors with a p-type GaN gate can be successfully controlled by inserting a SiNx insulator between the p-GaN and a Ni/Au electrode. The Vth can be controlled from +1 V to above +8 V. Moreover, the gate leakage current of transistors decreases and their gate voltage at which gate current steeply increases becomes higher. The mechanism of the threshold voltage change is analyzed by the equiv. circuit model.

AlGaN/GaN HFETs on Fe-doped GaN substrates Reviewed

Oshimura, Yoshinori; Takeda, Kenichiro; Sugiyama, Takayuki; Iwaya, Motoaki; Kamiyama, Satoshi; Amano, Hiroshi; Akasaki, Isamu; Bandoh, Akira; Udagawa, Takashi

Physica Status Solidi C Vol. ７ ( ７－８ ) page： 1974-1976 2010.7

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

AlGaN/GaN HFETs with different undoped GaN thicknesses were grown on Fe-doped freestanding GaN substrates by conventional MOVPE. To realize a high drain current, thick undoped GaN is found to be necessary. SIMS measurement shows that Fe is redistributed into the epilayer, by which the scattering center is generated at the channel when the thickness of the undoped GaN is insufficient. We also obsd. a similar Fe profile in the GaN/sapphire template placed on the side of the Fe-doped GaN substrate during growth. Therefore, Fe in the Fe-doped GaN substrate is redistributed not only through a solid but also through vapor.

Growth and characterization of GaN grown on moth-eye patterned sapphire substrates Reviewed

Ishihara, Akihiro; Kawai, Ryousuke; Kitano, Thukasa; Suzuki, Atushi; Kondo, Toshiyuki; Iwaya, Motoaki; Amano, Hiroshi; Kamiyama, Satoshi; Akasaki, Isamu

Physica Status Solidi C Vol. 7 ( 7-8 ) page： 2056-2058 2010.7

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

To realize high-efficiency light-emitting diodes (LEDs), it is necessary to increase light extn. efficiency. Therefore, the introduction of a moth-eye structure, which consists of periodic cones with a pitch of optical wavelength magnitude, into a sapphire surface before the epitaxial growth of nitride films is very promising for reducing the reflectivity of light resulting in high light extn. efficiency. 450 nm GaInN/GaN LEDs were fabricated on conventional and moth-eye substrates by metal org. vapor phase epitaxy (MOVPE). The intensity of room-temp. photoluminescence emitted from the LED with the moth-eye-patterned sapphire substrate was 1.6 times higher than that emitted from the LED without the moth-eye substrate. Under a current injection of 50 mA, the output power of the moth-eye LED is 3.6 times higher than that of the conventional LED.
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Growth of GaInN by raised-pressure metalorganic vapor phase epitaxy Reviewed

Iida, Daisuke; Nagata, Kensuke; Makino, Takafumi; Iwaya, Motoaki; Kamiyama, Satoshi; Amano, Hiroshi; Akasaki, Isamu; Bandoh, Akira; Udagawa, Takashi

Applied Physics Express Vol. 3 ( 7 ) page： 075601/1-075601/2 2010.7

Growth of low-dislocation-density AlGaN using Mg-doped AlN underlying layer Reviewed

Asai, T.; Nonaka, K.; Ban, K.; Nagata, K.; Nagamatsu, K.; Iwaya, M.; Kamiyama, S.; Amano, H.; Akasaki, I.

Physica Status Solidi C Vol. 7 ( 7-8 ) page： 2101-2103 2010.7

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

We report on a new technol. for growing low-dislocation-d. AlGaN in which a Mg-doped AlN underlying layer is used. By growing AlxGa1-xN on AlN:Mg with AlN molar fractions x of 0.3, 0.5 and 0.7, the d. of misfit dislocations is much reduced compared with that in the case of growing AlGaN on undoped AlN. In addn., the surface becomes atomically flat.

Internal quantum efficiency of GaN/AlGaN-based multi quantum wells on different dislocation densities underlying layers Reviewed

Takeda, Kenichiro; Mori, Fumiaki; Ogiso, Yuji; Ichikawa, Tomoaki; Nonaka, Kentaro; Iwaya, Motoaki; Kamiyama, Satoshi; Amano, Hiroshi; Akasaki, Isamu

Physica Status Solidi C Vol. 7 ( 7-8 ) page： 1916-1918 2010.7

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

Internal quantum efficiency (IQE) of GaN/AlGaN multi quantum wells on the low dislocation d. Al0.25Ga0.75N grown by epitaxial lateral overgrowth (ELO) and facet controlled epitaxial lateral overgrowth were investigated by excitation intensity dependent photoluminescence measurement. The threading dislocation d. decreased from 4 × 109cm-2 to 2 × 108 cm-2 by using ELO method, then the IQE was much improved from 5% to 40% when the carrier d. was 1 × 1018 cm-3.

Mg-related acceptors in GaN Reviewed

Monemar, B.; Paskov, P. P.; Pozina, G.; Hemmingsson, C.; Bergman, J. P.; Amano, H.; Akasaki, I.; Figge, S.; Hommel, D.; et al.

Physica Status Solidi C Vol. 7 ( 7-8 ) page： 1850-1852 2010.7

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

Photoluminescence spectra of c-plane Mg doped GaN samples grown by MOVPE on bulk GaN templates reveal previously unknown properties, like the presence of several Mg-related acceptors. The use of unstrained samples allows a study of both bound exciton (BE) and donor-acceptor pair (DAP) spectra. Two main acceptors A1 and A2 are obsd. strongly in BE spectra as well as in DAP spectra, they have similar binding energies, i.e. about 220 meV. The common assignment of the deeper blue PL emission at 2.8-3.0 eV to a deep donor-shallow acceptor transition is questioned, and discussed in connection with the compensation problem in p-GaN. It seems like the Fermi level in p-GaN is controlled by a set of Mg-related acceptors at energies 0.2-0.6 eV from the valence band top.

Nitride-based light-emitting solar cell Reviewed

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

Physica Status Solidi C Vol. ７ ( 7-8 ) page： 1807-1809 2010.7

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

We report on the characteristics of a group-III-nitride-based solar cell. A GaInN/GaN double heterojunction p-i-n solar cell composed of a GaInN active layer sandwiched between n-type and p-type GaN layers was grown by metal-org. vapor phase epitaxy through an undoped GaN layer on (0001) sapphire substrate. The InN molar fraction of the GaInN active layer was detd. to be 11% from a secondary ion mass spectrometry profile. The max. external quantum efficiency reached 65%, and the internal quantum efficiency was 95% or more. This device emitted light after forward current injection. The PL peak almost corresponded to the absorption edge. However, the electroluminescence (EL) peak was at the wavelength much longer than the absorption edge. The open-circuit voltage is 1.51 V, the fill factor is 52%, and the short-circuit c.d. is 1.6 mA/cm2.

Study of two-dimensional electron gas in AlGaN channel HEMTs with high crystalline quality Reviewed

Hashimoto, Shin; Akita, Katsushi; Tanabe, Tatsuya; Nakahata, Hideaki; Takeda, Kenichiro; Amano, Hiroshi

Physica Status Solidi C Vol. 7 ( 7-8 ) page： 1938-1940 2010.7

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

Epitaxial structures of AlGaN channel high electron mobility transistors (HEMTs) were grown on sapphire and AlN substrates. Redn. in the full width at half max. of X-ray rocking curve for (10-12) peak of the AlGaN channel layer owing to the redn. of threading dislocation densities resulted in a sharp decrease in the sheet resistance of 2-dimensional electron gas (2DEG). In the case of AlGaN channel HEMTs, it was found that improvement of the cryst. quality of AlGaN channel layers is essential to the redn. of the sheet resistance of 2DEG. The use of AlN substrates resulted in improved cryst. quality of the AlGaN layer and lower 2DEG resistance, suggesting the high potential of AlN substrates for AlGaN channel HEMTs.

Improved efficiency of 255-280 nm AlGaN-based light-emitting diodes Reviewed

Pernot, Cyril; Kim, Myunghee; Fukahori, Shinya; Inazu, Tetsuhiko; Fujita, Takehiko; Nagasawa, Yosuke; Hirano, Akira; Ippommatsu, Masamichi; Iwaya, Motoaki; Kamiyama, Satoshi,Hiroshi Amano et al

Applied Physics Express Vol. 3 ( 6 ) page： 061004/1-061004/3 2010.6

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

We report on the fabrication and characterization of AlGaN-based deep UV light-emitting diodes (LEDs) with the emission wavelength ranging from 255-280 nm depending on the Al compn. of the active region. The LEDs were flip-chip bonded and achieved external quantum efficiencies of over 3% for all investigated wavelengths. Under cw operation, an output power of more than 1 mW at 10 mA was demonstrated. A moth-eye structure was fabricated on the back side of the Al2O3 substrate, and on-wafer output power measurement indicated a 1.5-fold improvement of light extn.

Compensation effect of Mg-doped a- and c-plane GaN films grown by metalorganic vapor phase epitaxy Reviewed

Iida, Daisuke; Tamura, Kenta; Iwaya, Motoaki; Kamiyama, Satoshi; Amano, Hiroshi; Akasaki, Isamu

Journal of Crystal Growth Vol. 312 ( 21 ) page： 3131-3135. 2010.6

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

The elec. and optical properties of Mg-doped a- and c-plane GaN films grown by MOVPE were systematically investigated. The photoluminescence spectra of Mg-doped a- and c-plane GaN films exhibit strong emissions related to deep donors when Mg doping concns. are above 1 × 1020 cm-3 and 5 × 1019 cm-3, resp. The elec. properties also indicate the existence of compensating donors because the hole concn. decreases at such high Mg doping concns. In addn., we estd. the ND/NA compensation ratio of a- and c-plane GaN by variable-temp. Hall effect measurement. The obtained results indicate that the compensation effect of the Mg-doped a-plane GaN films is lower than that of the Mg-doped c-plane GaN films.

Misfit strain relaxation in m-plane epitaxy of InGaN on ZnO Reviewed

Wu, Z. H.; Sun, K. W.; Wei, Q. Y.; Fischer, A. M.; Ponce, F. A.; Kawai, Y.; Iwaya, M.; Kamiyama, S.; Amano, H.; Akasaki, I.

Applied Physics Letters Vol. 96 ( ７ ) page： 071909/1-071909/3 2010.3

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

The microstructure of m-plane InGaN epilayers grown on m-plane ZnO has been found to depend significantly on indium content in the range from 0.07 to 0.17, where anisotropic lattice mismatch between InGaN and ZnO results in decreasingly tensile and increasingly compressive stress along the a and c lattice axes. For indium content below 0.10, periodic arrays of misfit dislocations with a Burgers vector of 1/3[11-20] are obsd. parallel to the [0001] direction. For indium content above 0.12, generation of basal-plane stacking faults relieve the compressive stress along the 0001 direction. These characteristic mechanisms of strain relaxation should provide new approaches to engineer thick InGaN layers with reduced lattice misfit strain.

Microstructure of AlN with two-domain structure on (001) diamond substrate grown by metal-organic vapor phase epitaxy Reviewed

Imura, Masataka, Nakajima, Kiyomi, Liao, Meiyong, Koide, Yasuo, Amano, Hiroshi

Diamond and Related Materials Vol. 19 ( 0 ) page： 131-133 2010.2

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

We investigate the microstructures of domain boundaries in an AlN layer grown on a (001) diamond substrate by metal-org. vapor phase epitaxy. The AlN layer has a two-domain structure with crystal orientation along either <112-0> AlN [named by AlNI domain] or <101-0> AlN [named by AlNII domain] parallel to [110] direction of diamond. The AlNI and AlNII domains are not atomically bonded at two-domain boundary from initial to final step of growth, while an edge-type dislocation is generated at single-domain boundary (SDB). In addn., an inversion AlNI domain [named by AlNI*] is randomly-ordered at the initial stage of the coalescence between the AlNI domains. The AlNI* is easily terminated with increasing the thickness of AlNI domain. The inversion domain boundary changes to the edge-type dislocation at the SDB with further growth, which reduces the defect d. in the AlNI domains.

High-output-power AlGaN/GaN ultraviolet-light-emitting diodes by activation of Mg-doped p-type AlGaN in oxygen ambient Reviewed

Nagata, Kengo, Ichikawa, Tomoki, Takeda, Kenichiro, Nagamatsu, Kentaro, Iwaya, Motoaki, Kamiyama, Satoshi, Amano, Hiroshi, Akasaki, Isamu

Physica Status Solidi A: Vol. 207 ( 0 ) page： 1393-1396 2010

Compensation effect of Mg-doped a- and c-plane GaN films grown by metalorganic vapor phase epitaxy Reviewed

Iida, Daisuke; Tamura, Kenta; Iwaya, Motoaki; Kamiyama, Iida, Daisuke; Tamura, Kenta; Iwaya, Motoaki; Kamiyama, Satoshi; Amano, Hiroshi; Akasaki, Isamu

Journal of Crystal Growth Vol. 312 ( 21 ) page： 3131-3135 2010

Defects in highly Mg-doped AlN Reviewed

Nonaka, Kentaro, Asai, Toshiaki, Nagamatsu, Kentaro, Iwaya, Motoaki, Kamiyama, Satoshi, Amano, Hiroshi, Akasaki, Isamu

Physica Status Solidi A Vol. 207 ( 0 ) page： 1299-1301 2010

Growth mechanism of c-axis-oriented AlN on (001) diamond substrates by metal-organic vapor phase epitaxy Reviewed

Imura, Masataka, Nakajima, Kiyomi, Liao, Meiyong, Koide, Yasuo, Amano, Hiroshi

Journal of Crystal Growth Vol. 312 ( 0 ) page： 368-372 2010

Growth mechanism of c-axis-oriented AlN on (111) diamond substrates by metal-organic vapor phase epitaxy Reviewed

Imura, Masataka, Nakajima, Kiyomi, Liao, Meiyong, Koide, Yasuo, Amano, Hiroshi

Journal of Crystal Growth Vol. 312 ( 0 ) page： 1325-1328 2010

P-type doping and defect generation in Group III nitride semiconductors Invited Reviewed

Amano, Hiroshi; Iwaya, Motoaki; Kamiyama, Satoshi; Akasaki, Isamu

Nippon Kessho Seicho Gakkaishi Vol. 36 ( 3 ) page： 200-204 2009.3

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Papers - AMANO, Hiroshi