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Yamada, Takahiro*; Watanabe, Kenta*; Nozaki, Mikito*; Shih, H.-A.*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.
Japanese Journal of Applied Physics, 57(6S3), p.06KA07_1 - 06KA07_6, 2018/06
Times Cited Count:6 Percentile:29.42(Physics, Applied)Thermal oxidation of AlGaN surface and its impact on the electrical properties of AlGaN/GaN MOS capacitors were investigated by means of synchrotron radiation photoelectron spectroscopy (SR-PES), atomic force microscopy (AFM) and C-V measurements. SR-PES analysis revealed that the AlGaN surface is oxidized even at low temperature of 400C, in contrast to no oxide formation on GaN surface. However, since no noticeable change in the surface morphology was observed at temperatures up to 800C, it can be concluded that an ultrathin oxide overlayer is formed on the AlGaN surface. On the other hand, for the oxidation treatments above 850C, the formation of small oxide grains was observed over the entire area of the AlGaN surface, and the growth of oxide grains significantly degraded the surface morphology. Therefore, the AlGaN/GaN MOS capacitors were fabricated on the AlGaN surface oxidized at moderate temperatures up to 800C. While we have confirmed that relatively good interface properties are obtained for direct AlON deposition without oxidation treatment, it was found that the oxidation treatment at 400C leads to further improvement of interface properties and reduction of C-V hysteresis.
Nozaki, Mikito*; Watanabe, Kenta*; Yamada, Takahiro*; Shih, H.-A.*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.
Japanese Journal of Applied Physics, 57(6S3), p.06KA02_1 - 06KA02_7, 2018/06
Times Cited Count:19 Percentile:66.48(Physics, Applied)We fabricated AlON dielectric films by repeating thin AlN deposition and in situ O oxidation for AlGaN/GaN MOS-HFETs. Uniform nitrogen distribution is achievable by the proposed ALD-based process and that nitrogen concentration can be precisely controlled by changing AlN thickness (ALD cycle number) in each step. It was found that AlON films grown by ALD system offers significant advantages in terms of practical application while keeping superior Vth stability and electrical properties at the insulator/AlGaN interface in AlGaN/GaN MOS-HFETs.
Watanabe, Kenta*; Terashima, Daiki*; Nozaki, Mikito*; Yamada, Takahiro*; Nakazawa, Satoshi*; Ishida, Masahiro*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; et al.
Japanese Journal of Applied Physics, 57(6S3), p.06KA03_1 - 06KA03_6, 2018/06
Times Cited Count:10 Percentile:45.14(Physics, Applied)The advantage of SiO/AlON stacked gate dielectrics over SiO, AlON and AlO single dielectric layers was demonstrated. Our systematic research revealed that the optimized stacked structure with 3.3-nm-thick AlON interlayer is beneficial in terms of superior interface quality, reduced gate leakage current and C-V hysteresis for next-generation high frequency and high power AlGaN/GaN MOS-HFETs.
Watanabe, Kenta*; Nozaki, Mikito*; Yamada, Takahiro*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ishida, Masahiro*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.
Applied Physics Letters, 111(4), p.042102_1 - 042102_5, 2017/07
Times Cited Count:16 Percentile:59.74(Physics, Applied)AlGaN/GaN HFET (hetero-junction field-effect transitor) has gained much attention as next-generation high frequency and high power devices. In this study, we systematically investigated the interface reaction between Al-based dielectrics (AlO and AlON) and AlGaN layer during deposition and post-deposition annealing (PDA), and revealed high thermal stability of AlON/AlGaN interface.
Yamada, Takahiro*; Ito, Joyo*; Asahara, Ryohei*; Watanabe, Kenta*; Nozaki, Mikito*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ishida, Masahiro*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; et al.
Journal of Applied Physics, 121(3), p.035303_1 - 035303_9, 2017/01
Times Cited Count:67 Percentile:91.92(Physics, Applied)Initial oxidation of GaN(0001) epilayers and subsequent growth of thermal oxides in dry oxygen ambient were investigated by means of X-ray photoelectron spectroscopy, spectroscopic ellipsometry, atomic force microscopy and X-ray diffraction measurements. It was found that, whereas initial oxide formation tends to saturate at temperatures below 800C, selective growth of small oxide grains proceeds at dislocations in the epilayers, followed by noticeable grain growth leading to rough surface morphology at higher oxidation temperatures. This indicates that oxide growth and its morphology are crucially dependent on the defect density in the GaN epilayers. Structural characterizations also revealed that polycrystalline - and -phase GaO grains in an epitaxial relation with the GaN substrate are formed from the initial stage of the oxide growth. On the basis of these experimental findings, we also developed a comprehensive model for GaN oxidation mediated by nitrogen removal and mass transport.
Ide, Takayuki*; Kawai, Yusuke*; Handa, Hiroyuki*; Fukidome, Hirokazu*; Kotsugi, Masato*; Okochi, Takuo*; Enta, Yoshiharu*; Kinoshita, Toyohiko*; Yoshigoe, Akitaka; Teraoka, Yuden; et al.
Japanese Journal of Applied Physics, 51(6), p.06FD02_1 - 06FD02_4, 2012/06
Times Cited Count:7 Percentile:30.27(Physics, Applied)Fukidome, Hirokazu*; Abe, Shunsuke*; Takahashi, Ryota*; Imaizumi, Kei*; Inomata, Shuya*; Handa, Hiroyuki*; Saito, Eiji*; Enta, Yoshiharu*; Yoshigoe, Akitaka; Teraoka, Yuden; et al.
Applied Physics Express, 4(11), p.115104_1 - 115104_3, 2011/11
Times Cited Count:35 Percentile:78.24(Physics, Applied)Fukidome, Hirokazu*; Takahashi, Ryota*; Abe, Shunsuke*; Imaizumi, Kei*; Handa, Hiroyuki*; Kang, H. C.*; Karasawa, Hiromi*; Suemitsu, Tetsuya*; Otsuji, Taiichi*; Enta, Yoshiharu*; et al.
Journal of Materials Chemistry, 21(43), p.17242 - 17248, 2011/11
Times Cited Count:28 Percentile:63.08(Chemistry, Physical)Imaizumi, Kei*; Handa, Hiroyuki*; Takahashi, Ryota*; Saito, Eiji*; Fukidome, Hirokazu*; Enta, Yoshiharu*; Teraoka, Yuden; Yoshigoe, Akitaka; Suemitsu, Maki*
Japanese Journal of Applied Physics, 50(7), p.070105_1 - 070105_6, 2011/07
Times Cited Count:4 Percentile:18.91(Physics, Applied)Konomura, Mamoru; Ogawa, Takashi; Okano, Yasushi; Yamaguchi, Hiroyuki; Murakami, Tsutomu; Takaki, Naoyuki; Nishiguchi, Youhei; Sugino, Kazuteru; Naganuma, Masayuki; Hishida, Masahiko; et al.
JNC TN9400 2004-035, 2071 Pages, 2004/06
The attractive concepts for Sodium-, lead-bismuth-, helium- and water-cooled FBRs have been created through using typical plant features and employing advanced technologies. Efforts on evaluating technological prospects of feasibility have been paid for these concepts. Also, it was comfirmed if these concepts satisfy design requierments of capability and performance presumed in the feasibilty study on commertialization of Fast Breeder Reactor Systems. As results, it was concluded that the selection of sodium-cooled reactor was most rational for practical use of FBR technologies in 2015.
Nozaki, Mikito*; Watanabe, Kenta*; Yamada, Takahiro*; Shih, H.*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.
no journal, ,
We fabricated AlON dielectric films by repeating thin AlN deposition and in situ O oxidation for AlGaN/GaN MOS-HFETs. Uniform nitrogen distribution is achievable by the proposed ALD-based process and that nitrogen concentration can be precisely controlled by changing AlN thickness (ALD cycle number) in each step. It was found that AlON films grown by ALD system offers significant advantages in terms of practical application while keeping superior Vth stability and electrical properties at the insulator/AlGaN interface in AlGaN/GaN MOS-HFETs.
Watanabe, Kenta*; Terashima, Daiki*; Nozaki, Mikito*; Yamada, Takahiro*; Nakazawa, Satoshi*; Ishida, Masahiro*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; et al.
no journal, ,
The advantage of SiO/AlON stacked gate dielectrics over SiO, AlON and AlO single dielectric layers was demonstrated. Our systematic research revealed that the optimized stacked structure with 3.3-nm-thick AlON interlayer is beneficial in terms of superior interface quality, reduced gate leakage current and C-V hysteresis for next-generation high frequency and high power AlGaN/GaN MOS-HFETs.
Watanabe, Kenta*; Nozaki, Mikito*; Yamada, Takahiro*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ishida, Masahiro*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.
no journal, ,
AlGaN/GaN HFET has gained much attention as next-generation high frequency and high power devices. Among various insulating materials, AlO is one of the potential candidates. However, large amount of electrical defects at MOS interfaces severely degrade both drive current and threshold voltage stability. Positive Vth shift due to electron trapping in AlO layer by applying positive gate bias is often observed for AlO/AlGaN/GaN MOS structures. We have recently reported that N incorporation into AlO significantly reduces electron traps in AlO layer for Si and SiC MOS devices. In this study, we systematically investigated the interface reaction between Al-based dielectrics (AlO and AlON) and AlGaN layer during deposition and post-deposition annealing (PDA), and revealed high thermal stability of AlON/AlGaN interface.
Watanabe, Kenta*; Yamada, Takahiro*; Nozaki, Mikito*; Nakazawa, Satoshi*; Shih, H.*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.
no journal, ,
Initial oxidation process of AlGaN surface during thermal oxidation was investigated by synchrotron radiation photoelectron spectroscopy. Thermal oxidation of AlGaN/GaN/Si(111) substrates was carried out for 30 min in the temperature range from 200 to 1000 degrees in O ambient. The obtained Ga 2p spectra exhibited peak shift toward the higher binding energy with increasing oxidation temperature, suggesting the growth of Ga oxides on AlGaN surface. The peak deconvolution of Ga 2p spectra into Ga-O and Ga-N components revealed that the formation of Ga oxides was formed on AlGaN surface at above 400 degrees while GaN surface was stable below 600 degrees. These results indicate that AlGaN surface is easy to be oxidized compared to GaN surface.
Terashima, Daiki*; Watanabe, Kenta*; Yamada, Takahiro*; Nozaki, Mikito*; Shih, H.*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; et al.
no journal, ,
Impact of input power and substrate temperature of SiO deposition by plasma-enhanced CVD on SiO/AlGaN interface was investigated by means of electrical characterization of MOS capacitors. Synchrotron radiation photoemission spectroscopy revealed that Ga oxide component on AlGaN surface increases with increasing input power of PECVD. MOS capacitors with SiO gate insulator deposited at low input power shows relatively better SiO/AlGaN interface quality, despite degraded interface quality for the sample with SiO deposited at high input power. These results suggest that AlGaN surface oxidation during oxide deposition should be controlled to obtain good interface property.
Watanabe, Kenta*; Nozaki, Mikito*; Yamada, Takahiro*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ishida, Masahiro*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.
no journal, ,
AlGaN/GaN HFET (hetero-junction field-effect transitor) has gained much attention as next-generation high frequency and high power devices. Since AlGaN/GaN HFET with Schottky gate is restricted in device application due to large gate leakage current and normally-on operation, MOS gate stack with deposited gate insulator has been widely investigated to overcome these limitations. Among various insulating materials, AlO is one of the potential candidates because of its wide bandgap and high thermal stability. In this study, we systematically investigated the interface reaction between Al-based dielectrics (AlO and AlON) and AlGaN layer during deposition and post-deposition annealing (PDA), and revealed high thermal stability of AlON/AlGaN interface.
Yamada, Takahiro*; Yoshigoe, Akitaka; Ito, Joyo*; Asahara, Ryohei*; Watanabe, Kenta*; Nozaki, Mikito*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ishida, Masahiro*; Ueda, Tetsuzo*; et al.
no journal, ,
Thermal oxidation process of self-standing GaN (ss-GaN) substrates with low-defect density were investigated by atomic force microscopy and synchrotron radiation photoelectron spectroscopy. ss-GaN sample showed a flat surface morphology without pits which are ascribed to dislocation defects in the measured area (1 mx1 m). Therefore, the preferential formation of Ga-oxides at the pits was not observed by thermal oxidation, and the flat surface morphology was kept in the sample oxidized at 800C (the root-mean-square (RMS) roughness of 0.14 nm). However, the ss-GaN sample oxidized at 900C showed rough surface morphology due to the formation of small Ga-oxide grains (RMS roughness of 0.62 nm). The grains drastically grew at 1000C, resulted in the surface morphology consisting of -GaO crystal.