論文 - 鈴木 秀俊
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Yamaguchi M., Suzuki H., Ohshita Y., Kojima N., Takamoto T.
Conference Record of the IEEE Photovoltaic Specialists Conference 1237 - 1242 2010年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the IEEE Photovoltaic Specialists Conference
III-V compound multi-junction solar cells have great potential for space and terrestrial applications because they have high efficiency potential of more than 50% and superior radiation-resistance. We have been studying concentrator multi-junction solar cells under Japanese Innovative Photovoltaic R & D program started since FY2008. This paper presents our new achievements in super high-efficiency multi-junction and concentrator solar cells. We have obtained promising results: 1) 35.8% efficiency InGaP/GaAs/InGaAs 3-junction cells, 2) high quality (In)GaAsN material with higher mobility by chemical beam epitaxy compared to those grown by the other growth methods. © 2010 IEEE.
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Low temperature growth GaAs on GE by chemical beam epitaxy
Lee J., Suzuki H., Han X., Inagaki M., Ikeda K., Kojima N., Ohshita Y., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2070 - 2073 2010年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the IEEE Photovoltaic Specialists Conference
Hetero-epitaxy of GaAs films on Ge were grown by the chemical beam epitaxy (CBE) technique for super-high-efficiency multi-junction solar cells. However, the growth of III-V on Ge remains a key challenge due to anti-phase domains (APDs) and the inter-diffusion at the interface, resulting in the deterioration of the solar cell efficiency. In order to overcome these problems, we introduced the CBE technique, which was carried out under a higher vacuum (∼10 -2 Pa) and at relatively lower temperature (360∼460° C) as compared with the growth of GaAs on Ge by the typical metalorganic vapor phase epitaxy (MOVPE). The effects of the low growth temperature, the source flow ratio of [V/III] and pre-annealing temperature on crystal qualities and optical properties of GaAs films on Ge were investigated. The results showed that GaAs films on Ge had a good structural quality at growth temperature from 400 to 460 °C with the [V/III] of flow ratio from 50 to 70 by a high resolution x-ray diffraction. The pre-annealing temperature and time were confirmed to play an important role in the modification of Ge substrate surface. The low-temperature (4.5 K) photoluminescence spectra showed the emission peak around 1.51 eV, corresponding to an exciton bound-to-acceptor, in sample grown at 400 °C and the full width at half maximum of this peak was evaluated 10 meV by Gaussian fitting. An emission peak of 1.27 eV caused by Ge diffusion into GaAs film was observed for the sample grown at 460 °C. Such a critical temperature that activates the Ge diffusion seems relatively low in CBE system as compared with that reported in MOVPE system. © 2010 IEEE.
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Improvement of minority-carrier lifetime in GaAsN grown by chemical beam epitaxy
Honda T., Inagaki M., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2053 - 2056 2010年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the IEEE Photovoltaic Specialists Conference
Minority-carrier lifetime (electron) in p-type GaAsN film is improved by chemical beam epitaxy (CBE) and thermal annealing. Growth rate (GR) in CBE is an important factor to improve minority-carrier lifetime in bulk (τ B ). For as-grown samples, τ B is increased from 3.2 × 10 2 ps (GR = 2 μm/h) to 9.0 × 10 2 ps (GR = 0.4 ×m/h). The obtained τ B is much longer than the minority-carrier lifetime (∼ 10 1 ps) predicted by the reported carrier diffusion length and mobility. This improvement is due to the increase of nonradiative recombination lifetime (τ NR ) caused by the decrease of nonradiative recombination centers. By thermal annealing, PL lifetime (τ PL ) is increased. Therefore, CBE and thermal annealing have a high possibility to obtain the minority-carrier lifetime required to solar cells ( > 1 ns). © 2010 IEEE.
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Identification of N-H related defects in GaAsN grown by chemical beam epitaxy
Tanaka T., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2120 - 2124 2010年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the IEEE Photovoltaic Specialists Conference
Three infrared active defects in GaAsN grown by chemical beam epitaxy (CBE) are identified as N-H related defects which are determinative of electrical property of (In)GaAsN. One N-H related defect is also observed in GaAsN grown by metalorganic chemical-vapor deposition (MOCVD). However other two N-H related defects are only observed in GaAsN grown by CBE. Therefore there is possibility that these two defects are characteristic defects of CBE. We also clarify number of hydrogen in the N-H related defects which is important factor of the defects' electrical property. One N-H related defect includes two hydrogens and two N-H related defects include one hydrogen, respectively. These results are derived by using deuterated N source. © 2010 IEEE.
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IN situ 3D X-RAY reciprocal space mapping during lattice-mismatched InGaAs/GaAs growth
Sasaki T., Suzuki H., Sai A., Ohshita Y., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 695 - 698 2010年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the IEEE Photovoltaic Specialists Conference
In situ three dimensional X-ray reciprocal space map (3D-RSM) measurement during InGaAs/GaAs(001) molecular beam epitaxial (MBE) growth is performed for the first time to investigate the anisotropies in relaxation processes along [110] and [110] direction caused by α and β misfit dislocations (MDs).The 3D-RSM is obtained by an X-ray diffractometer directly coupled to the MBE system in SPring-8. As the anisotropies, line dislocation densities and crystal qualities of both directions are simultaneously evaluated from position and broadness of 022 diffraction in the 3D-RSM, respectively. We demonstrated that 3D-RSM is a useful characterization technique to investigate anisotropies in dislocation behaviour and in relaxation processes, and believed that the fundamental knowledge obtained in this study will be important to design the metamorphic III-V solar cells with lower threading dislocation density. © 2010 IEEE.
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Bouzazi B., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Japanese Journal of Applied Physics 49 ( 12 ) 2010年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Japanese Journal of Applied Physics
The properties of a nitrogen (N)-related hole trap HC2, located approximately 0.15 eV above the valence band maximum of GaAsN, and their relationship with the density of ionized acceptors (N A ) in p-type GaAsN grown by chemical beam epitaxy are investigated using deep level transient spectroscopy and on the basis of the temperature dependence of the junction capacitance. At room temperature, N A is found to show a linear dependence on N concentration under N- and H-rich growth conditions. Furthermore, a N-dependent sigmoid increase in junction capacitance is observed in a specific temperature range from 70 to 100 K, which is the same as in the case where HC2 is recorded. Such behavior is explained by the thermal ionization of HC2, whose density affects in great part the magnitude order of N A , essentially for a N concentration higher than 0.15%. Concerning its origin, HC2 is strongly considered to act as N-H related acceptor state. © 2010 The Japan Society of Applied Physics.
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Sasaki T., Suzuki H., Sai A., Takahasi M., Fujikawa S., Ohshita Y., Yamaguchi M.
Materials Research Society Symposium Proceedings 1268 45 - 50 2010年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Materials Research Society Symposium Proceedings
The in situ X-ray reciprocal space mapping (in situ RSM) of symmetric diffraction measurements during lattice-mismatched InGaAs/GaAs(001) growth were performed to investigate the strain relaxation mechanisms. The evolution of the residual strain and crystal quality were obtained as a function of InGaAs film thickness. Based on the results, the correlation between the strain relaxation and the dislocations during the film growth were evaluated. As a result, film thickness ranges with different relaxation mechanisms were classified, and dominant dislocation behavior in each phase were deduced. From the data obtained in in situ measurements, the quantitative strain relaxation models were proposed based on a dislocation kinetic model developed by Dodson and Tsao. Good agreement between the in situ data and the model ensured the validity of the dominant dislocation behavior deduced from the present study. © 2010 Materials Research Society.
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Relation between N-H complexes and electrical properties of GaAsN determined by H implantation
Lee J., Suzuki H., Han X., Honda K., Tanaka T., Hwang J., Bouzazi B., Inagaki M., Kojima N., Ohshita Y., Yamaguchi M.
Current Applied Physics 10 ( SUPPL. 3 ) 2010年8月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Current Applied Physics
We investigated the relation between N-H complexes and the electrical properties of GaAsN, which is a potential material for fabricating super-high-efficiency multi-junction tandem solar cells. In order to separate the effect of other residual carrier such as carbon in a GaAsN film on the electrical properties, hydrogen (H) ions were implanted into GaAsN grown by chemical beam epitaxy (CBE) and then rapid thermal annealing from 250 to 650 °C was carried out. Two N-H complexes related to local vibrational modes (LVMs) in GaAsN were observed at 3098 and 3125 cm -1 . With an increasing annealing temperature, the integrated peak intensity of the 3098 cm -1 peak (I 3098 ) decreased, while that of the 3125 cm -1 peak (I 3125 ) increased. This indicates that N-H complexes related to the 3125 cm -1 peak are thermally more stable than those related to the other peak. The hole concentrations and mobilities exhibited an increasing trend until an annealing temperature of 550 °C was reached. Their increases are attributed to the removal of donor-type defects. It is suggested that the N-H complexes related to the 3098 cm -1 peak are electrically active, while those giving the 3125 cm -1 peak are inactive. © 2010 Elsevier B.V. All rights reserved.
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Suzuki H., Sasaki T., Sai A., Ohshita Y., Kamiya I., Yamaguchi M., Takahasi M., Fujikawa S.
Applied Physics Letters 97 ( 4 ) 2010年7月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Applied Physics Letters
Real-time three-dimensional reciprocal space mapping (3D-RSM) measurement during In 0.12 Ga 0.88 As/GaAs (001) molecular beam epitaxial growth has been performed to investigate anisotropy in relaxation processes along [110] and [1̄10] directions caused by α and β misfit dislocations (MDs). Anisotropies, strain relaxation, and crystal quality in both directions were simultaneously evaluated via the position and broadness of 022 diffraction in 3D-RSM. In the small-thickness region, strain relaxation caused by α -MDs is higher than that caused by β-MDs, and therefore crystal quality along [110] is worse than that along [1- 10] . Rapid relaxation along both [110] and [1̄10] directions occurs at almost the same thickness. After rapid relaxation, anisotropy in strain relaxation gradually decreases, whereas crystal quality along [1̄10] direction, presumably due to β-MDs, becomes better that along [110] direction and the ratio does not decay with thickness. © 2010 American Institute of Physics.
DOI： 10.1063/1.3458695
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Bouzazi B., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Applied Physics Express 3 ( 5 ) 2010年5月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Applied Physics Express
A nitrogen-related electron trap, at around 0.3eV from the conduction band minimum of n-type GaAsN grown by chemical beam epitaxy, is confirmed using deep level transient spectroscopy and nitrogen concentration dependence of its density. It has a high capture cross section and not observed in N free n-type GaAs. Furthermore, its density increases markedly with increasing N, persists to post thermal annealing, and found to be quasi-uniform distributed in the bulk of GaAsN. Based on first-principles calculation, the electron trap is associated with a split interstitial defect formed from N and As atoms on the same As lattice site (As-N) As . © 2010 The Japan Society of Applied Physics.
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Nitrogen-related recombination center in GaAsN grown by chemical beam epitaxy
Bouzazi B., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Japanese Journal of Applied Physics 49 ( 5 PART 1 ) 0510011 - 0510014 2010年5月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Japanese Journal of Applied Physics
A nitrogen-related deep electron trap, at approximately 0.33 eV below the conduction band minimum of GaAsN grown by chemical beam epitaxy, is confirmed to act as a recombination center. The level is found to be responsible for the reverse bias current in the depletion region of n-type GaAsN schottky junction and N + -GaAs/p-GaAsN heterojunction, where the current is due mainly to electrons. This result is obtained by correlating the thermal activation energy of the reverse bias current and the activation energy of electron traps, investigated in the two structures by deep level transient spectroscopy. © 2010 The Japan Society of Applied Physics.
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Suzuki H., Inagaki M., Honda T., Ohshita Y., Kojima N., Yamaguchi M.
Japanese Journal of Applied Physics 49 ( 4 PART 2 ) 2010年4月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Japanese Journal of Applied Physics
Improvements in optoelectrical properties of GaAsN are demonstrated by chemical beam epitaxy (CBE) growth on high-step-density GaAs substrates. The step density at the growing surface is controlled using 2, 4, and 10° off GaAs(001) wafers as substrates. The number of carrier scattering centers induced by N (SC N ) in the grown GaAsN films is quantitatively evaluated from the temperature dependence of hole mobility and used as an indicator of film quality. In previous studies, SC N increased with increasing N composition independently of the growth technique used. By CBE with high-step-density substrates, the reduction in SC N is achieved. This method also improves the emission intensity of cathode luminescence. © 2010 The Japan Society of Applied Physics.
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Bouzazi B., Nishimura K., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Current Applied Physics 10 ( 2 SUPPL. ) 2010年3月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Current Applied Physics
The minority carrier diffusion length in Chemical Beam Epitaxy (CBE) grown GaAs 0.995 N 0.005 based homo-junction solar cell was estimated and found to be L = 0.08 μm. In addition, the majority carrier traps in N-varying unintentionally doped p-type GaAsN samples grown by CBE were investigated using Deep Level Transient Spectroscopy (DLTS) technique. Five hole traps, HC1-HC5, were detected, where HC2 and HC5 coexist in all samples. These two hole traps were suggested to be a N-related defect and the double donor state of EL2, respectively. © 2009 Elsevier B.V. All rights reserved.
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Novel materials for high-efficiency solar cells
Kojima N., Natori M., Suzuki H., Inagaki M., Ohshita Y., Yamaguchi M.
Proceedings of SPIE - The International Society for Optical Engineering 7518 2009年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering
Our Toyota Technological Institute group has investigated various novel materials for solar cells from organic to III-V compound materials. In this paper, we report our recent results in conductivity control of C 60 thin films by metal-doping for organic solar cells, and mobility improvement of (In)GaAsN compounds for III-V tandem solar cells. The epitaxial growth of Mg-doped C 60 films was attempted. It was found that the epitaxial growth of Mg-doped C 60 film was enabled by using mica (001) substrate in the low Mg concentration region (Mg/C 60 molar ratio < 1). The crystal quality of the epitaxial Mg-doped C 60 film was improved drastically in compared with micro-crystalline film on glass substrate. Such drastic improvement of crystal quality in the epitaxial films resulted significant increase in conductivity. This result may indicate the significant increase of carrier mobility. Crystal quality improvement of CBE-grown GaAsN materials was investigated. We achieved the reduction of residual impurity concentration by chemical reaction control on the growing surface by modifying flow sequence of precursors and by increasing step density on the surface by using a vicinal GaAs substrate. Furthermore, the improvement in carrier mobility was observed, and it was suggested that the reduction of both residual impurities and N-related defects leads this improvement. © 2009 Copyright SPIE - The International Society for Optical Engineering.
DOI： 10.1117/12.845456
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Real-time study of strain relaxation in lattice-mismatched ingaas/gaas by x-ray diffraction
Sasaki T., Suzuki H., Sai A., Lee J., Takahasi M., Fujikawa S., Arafune K., Kamiya I., Ohshita Y., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 000999 - 001003 2009年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the IEEE Photovoltaic Specialists Conference
In situ real-time x-ray diffraction measurements during In 0.12 Ga 0.88 As/GaAs(001) epitaxial growth are performed for the first time to understand the strain relaxation mechanisms in a lattice-mismatched system. The reciprocal space maps of 004 diffractions are obtained, and allow us to evaluate the evolution of residual strain and crystal quality simultaneously as a function of layer thickness. In the time evolution, we have classified five thickness ranges, and deduced the dominant dislocation behavior in each phase. ©2009 IEEE.
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Local vibration modes of N-H related complexes in GaAsN grown by chemical beam epiaxy
Suzuki H., Tanaka T., Ohshita Y., Kojima N., Yamaguchi M.
ECS Transactions 25 ( 12 ) 123 - 127 2009年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ECS Transactions
The local vibration modes of N-H bonds Fourier transform infrared spectrometry for GaAsN films grown by chemical beam epitaxy are investigated. Four stretching modes of N-H bonds exist in the films. The absorption intensities of stretching modes at 3125, 3098 and 2952 cm -1 have no relationships, suggesting that at least three kinds of N-H related defects are formed in the GaAsN films. Major stretching modes are 3098 and 2952 cm -1 . The integrated absorption (IA) of 3098 cm -1 is proportional to H concentration ([H]). The IA of 2952 cm -1 changes super linearly with [H]. A simple N-H bond and a complex defect including N-H are suggested as the origin of 3098 and 2952 cm -1 , respectively. ©The Electrochemical Society.
DOI： 10.1149/1.3238216
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Hole mobility of GaAs<inf>1-X</inf>N<inf>X</inf> grown by chemical beam epitaxy
Suzuki H., Hashiguchi T., Kojima N., Ohshita Y., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 000848 - 000851 2009年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the IEEE Photovoltaic Specialists Conference
N induced scattering in GaAs 1-x N x films are quantitatively investigated, and reduction of the scattering is demonstrated. The hole mobility of GaAsN films is separated to individual scattering processes by parameter fitting. The mobility limited by the N induced scattering is fitted by the function of μ N = K N T -(0.6±0.2) . The amount of N induced scattering center increases linearly with increasing N composition. These results suggest that the origin of induced scattering is point defect contained one N atom. In the case of GaAs (001) 10° off substarte, μ N -1 was lower than that grown on a 2° off substrate. It suggests that the hole mobility can be improved by using high step density substrate. ©2009 IEEE.
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Conductivity improvement of epitaxial-grown Mg-doped C60 thin films
Kojima N., Natori M., Suzuki H., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 000725 - 000728 2009年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the IEEE Photovoltaic Specialists Conference
The epitaxial growth of Mg-doped C 60 films has been investigated. It is found that the epitaxial growth of Mg-doped C 60 film is enabled by using mica (001) substrate in the low Mg concentration region (Mg/C 60 molar ratio < 1). The crystal quality of the epitaxial Mg-doped C 60 film is improved drastically in compared with micro-crystalline film on glass substrate. Such drastic improvement of crystal quality in the epitaxial films results significant increase in conductivity. This result may indicate the significant increase of carrier mobility. In addition, the relation between conductivity and Mg concentration suggests the possibility that two valence electrons per Mg atom contribute the electrical conduction. ©2009 IEEE.
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Yamaguchi M., Ohshita Y., Kojima N., Suzuki H., Bouzazi B.
Conference Record of the IEEE Photovoltaic Specialists Conference 002332 - 002335 2009年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Conference Record of the IEEE Photovoltaic Specialists Conference
Target of the Japanese Innovative Photovoltaics R & D Program started from fiscal year 2008 is to develop high efficiency solar cells with conversion efficiency of more than 40% and low electricity cost of less than 7 JPY/kWh until 2050. In this program, concentrator III-V compound multi-junction (MJ) tandem solar cells have great potential for high efficiencies of over 50% and low cost of less than 30JPY/W. InGaAsN material is good candidate for 4-6 junction solar cells. In our preliminary stage of our project, 2% and 11.3% efficiencies have been obtained with GaAsN p-n and InGaAsN p-i-n single-junction solar cells. In order to increase efficiency of single and 4-junction solar cells, it is very important to understand and reduce defects and impurities in the grown films. In this paper, characterization of the CBE (Chemical Beam Epitaxy)-grown GaAsN films by Hall effect and DLTS (Deep Level Transient Spectroscopy) measurements is presented. ©2009 IEEE.
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Sasaki T., Suzuki H., Sai A., Lee J., Takahasi M., Fujikawa S., Arafune K., Kamiya I., Ohshita Y., Yamaguchi M.
Applied Physics Express 2 ( 8 ) 2009年8月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Applied Physics Express
In situ real-time X-ray diffraction measurements during In 0.12 Ga 0.88 As/GaAs(001) epitaxial growth are performed for the first time to understand the strain relaxation mechanisms in a lattice-mismatched system. The high resolution reciprocal space maps of 004 diffraction obtained at interval of 6.2 nm thickness enable transient behavior of residual strain and crystal quality to be observed simultaneously as a function of InGaAs film thickness. From the evolution of these data, five thickness ranges with different relaxation processes and these transition points are determined quantitatively, and the dominant dislocation behavior in each phase is deduced. © 2009 The Japan Society of Applied Physics.