論文 - 鈴木 秀俊
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(In)GaAsN materials and solar cells for super-high-efficiency multijunction solar cells
Yamaguchi M., Bouzazi B., Suzuki H., Ikeda K., Kojima N., Ohshita Y.
Conference Record of the IEEE Photovoltaic Specialists Conference 831 - 834 2012年11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
We have been studying concentrator multi-junction solar cells under Japanese Innovative Photovoltaic R & D program since FY2008 and EU-Japan Collaborative Research on CPV since 2011. In order to realize 40% and 50% efficiency, new approaches for novel materials and structures are being studied. InGaAsN is one of appropriate materials for 4- or 5-junction solar cell configuration because this material can be lattice-matched to GaAs and Ge substrates. However, present InGaAsN single-junction solar cells have been inefficient because of low minority-carrier lifetime due to N-related recombination centers and low carrier mobility due to alloy scattering and non-homogeneity of N. Present (In)GaAsN single-junction solar cells have been inefficient because of low minority-carrier lifetime due to N-related recombination centers such as N-H-V Ga , (N-N) As and so on, and low carrier mobility due to alloy scattering and non-homogeneity of N. To solve above problems we have been developing the CBE technique. We have focused especially on the N incorporation in GaAsN thin films grown by CBE as a function of growth temperature and substrate orientation. We have also proposed a new flow-rate modulation CBE (FM-CBE) method in order to increase N incorporation and to reduce C and H incorporation in films. By adapting CBE technique to grow (In)GaAsN thin films, higher mobility and longer minority-carrier lifetime compared to those grown by the other growth methods have been achieved. According to these electrical properties, more than 15% efficiency is expected in CBE grown homo junction (In)GaAsN solar cell although only 7.2% efficiency (Jsc=15.1 mA/cm 2 , Voc=0.662 V, FF=0.65) GaAsN single-junction cells have been obtained. To solve above problems, We have characterized deep levels in grown GaAsN films by DLTS and defect behaviors have been clarified. © 2012 IEEE.
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High-speed three-dimensional reciprocal-space mapping during molecular beam epitaxy growth of InGaAs 査読あり
Hu W., Suzuki H., Sasaki T., Kozu M., Takahasi M.
Journal of Applied Crystallography 45 ( 5 ) 1046 - 1053 2012年10月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Journal of Applied Crystallography
This paper describes the development of a high-speed three-dimensional reciprocal-space mapping method designed for the real-time monitoring of the strain relaxation process during the growth of heterostructure semiconductors. Each three-dimensional map is obtained by combining a set of consecutive images, which are captured during the continuous rotation of the sample, and calculating the reciprocal-space coordinates from the detector coordinate system. To demonstrate the feasibility of this rapid mapping technique, the 022 asymmetric diffraction of an InGaAs/GaAs(001) thin film grown by molecular beam epitaxy was measured and the procedure for data calibration was examined. Subsequently, the proposed method was applied to real-time monitoring of the strain relaxation process during the growth of a thin-film heterostructure consisting of In 0.07 Ga 0.93 As and In 0.18 Ga 0.82 As layers consecutively deposited on GaAs(001). The time resolution of the measurement was 10 s. It was revealed that additional relaxation of the first In0.07Ga0.93As layer was induced by the growth of the second In 0.18 Ga 0.82 As layer within a short period of time corresponding to the deposition of only two monolayers of InGaAs.
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Investigation of the photovoltaic performance of the polycrystalline silicon p–n junction by a photothermal measurement 査読あり
Atsuhiko Fukuyama, Daisuke Ishibashi, Yohei Sato, Kentaro Sakai, Hidetoshi Suzuki, Kensuke Nishioka, Tetsuo Ikari
Journal of Non-Crystalline Solids 358 2206 - 2208 2012年9月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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高分解能X線回折法によるGaAs基板上のフッ化物薄膜結晶の評価
正木 宏和, 前田 幸治, 境 健太郎, 尾関 雅志, 鈴木 秀俊
宮崎大學工學部紀要 41 155 - 159 2012年7月
記述言語：日本語 掲載種別：研究論文（大学，研究機関等紀要）
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Sasaki T., Shimomura K., Suzuki H., Takahasi M., Kamiya I., Ohshita Y., Yamaguchi M.
Japanese Journal of Applied Physics 51 ( 2 PART 2 ) 02BP01 - 02BP01-3 2012年2月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Japanese Journal of Applied Physics
In-plane asymmetric strain relaxation in lattice-mismatched InGaAs/GaAs(001) heteroepitaxy is studied by in situ three-dimensional X-ray reciprocal space mapping. Repeating crystal growth and growth interruptions during measurements allows us to investigate whether the strain relaxation is limited at a certain thickness or saturated. We find that the degree of relaxation during growth interruption depends on both the film thickness and the in-plane directions. Significant lattice relaxation is observed in rapid relaxation regimes during interruption. This is a clear indication that relaxation is kinetically limited. In addition, relaxation along the [110] direction can saturate more readily than that along the [110] direction. We discuss this result in terms of the interaction between orthogonally aligned dislocations. © 2012 The Japan Society of Applied Physics.
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Real-time structural analysis of compositionally graded InGaAs/GaAs(0 0 1) layers
Sasaki T., Suzuki H., Inagaki M., Ikeda K., Shimomura K., Takahasi M., Kozu M., Hu W., Kamiya I., Ohshita Y., Yamaguchi M.
IEEE Journal of Photovoltaics 2 ( 1 ) 35 - 40 2012年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：IEEE Journal of Photovoltaics
Compositionally step-graded InGaAs/GaAs(001) buffers with overshooting (OS) layers were evaluated by several characterization techniques for higher efficiency metamorphic III-V multijunction solar cells. By high-resolution X-ray diffraction, we found that fully relaxed or tensile strained top layers can be obtained by choosing appropriate OS layer thickness. Moreover, from real-time structural analysis using in situ X-ray reciprocal space mapping (in situ RSM), it was proved that the top layer is almost strained to the OS layers, and it is independent of the thicknesses of the OS layers. Dislocations in the vicinity of the OS layers were observed by transmission electron microscopy, and the validity of results of in situ RSM was confirmed from the viewpoint of misfit dislocation behavior. Finally, by photoluminescence measurements, we showed that tensile strained top layers may be suitable for the improvement of minority-carrier lifetime. © 2011 IEEE.
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Sasaki T., Suzuki H., Takahasi M., Ohshita Y., Kamiya I., Yamaguchi M.
Journal of Applied Physics 110 ( 11 ) 2011年12月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Journal of Applied Physics
Dislocation-mediated strain relaxation during lattice-mismatched InGaAs/GaAs(001) heteroepitaxy was studied through in situ x-ray reciprocal space mapping (in situ RSM). At the synchrotron radiation facility SPring-8, a hybrid system of molecular beam epitaxy and x-ray diffractometry with a two-dimensional detector enabled us to perform in situ RSM at high-speed and high-resolution. Using this experimental setup, four results in terms of film properties were simultaneously extracted as functions of film thickness. These were the lattice constants, the diffraction broadenings along in-plane and out-of-plane directions, and the diffuse scattering. Based on correlations among these results, the strain relaxation processes were classified into four thickness ranges with different dislocation behavior. In addition, the existence of transition regimes between the thickness ranges was identified. Finally, the dominant dislocation behavior corresponding to each of the four thickness ranges and transition regimes was noted. © 2011 American Institute of Physics.
DOI： 10.1063/1.3664832
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Bouzazi B., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 000454 - 000458 2011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
Two nitrogen-related lattice defects were confirmed in GaAsN grown by chemical beam epitaxy (CBE), using deep level transient spectroscopy (DLTS). The first defect is a non-radiative recombination center (E1), with average activation energy of 0.33 eV below the conduction band minimum (CBM) of GaAsN. The lifetime of electrons from the CBM to E1 was calculated to around ∼0.2 ns, using the Shockley-Read-Hall (SRH) model for generation-recombination. These results expected E1 as the main cause of short minority carrier lifetime in GaAsN films. The Second defect is a hole trap (H2), deep acceptor-like state, with average activation energy of 0.15 eV above the valence band maximum (VBM), and originates from the N-H bond. Its density was found to be in good relationship with free hole concentration in p-type films, which were grown under N and H rich growth conditions. This deep acceptor was suggested to be the main cause of high background doping in GaAsN, which prevents the design of a wide depletion region GaAsN based solar cells and drops the minority carrier lifetime. © 2011 IEEE.
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Effect of low growth rate in chemical beam epitaxy on carrier mobility and lifetime of p-GaAsN films 査読あり
Honda T., Ikeda K., Inagaki M., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Japanese Journal of Applied Physics 50 ( 8 PART 3 ) 08KD06 - 08KD06-4 2011年8月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Japanese Journal of Applied Physics
Decreasing the growth rate in chemical beam epitaxy (CBE) is effective to improve the hole mobility and minority-carrier lifetime in p-GaAsN films. The hole mobility increased from 120 to 150 cm 2 V -1 s -1 for the N composition of 0.6%. The minority-carrier lifetime improved from 3:2 × 10 -1 ([N] = 0:6%) to 9:0 × 10 -1 ns ([N] = 0:8%) despite the higher N composition. N-related scattering centers are indicated to be the dominant scattering centers at approximately room temperature. Controlling the growth rate is considered to be effective to reduce the amount of N-related scattering centers and nonradiative recombination centers. © 2011 The Japan Society of Applied Physics.
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Growth temperature dependence of strain relaxation during InGaAs/GaAs(0 0 1) heteroepitaxy 査読あり
Sasaki T., Suzuki H., Sai A., Takahasi M., Fujikawa S., Kamiya I., Ohshita Y., Yamaguchi M.
Journal of Crystal Growth 323 ( 1 ) 13 - 16 2011年5月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Journal of Crystal Growth
Growth temperature dependence of strain relaxation during In 0.12 Ga 0.88 As/GaAs(0 0 1) molecular beam epitaxy was studied by in situ X-ray reciprocal space mapping. Evolution of the residual strain and crystal quality for the InGaAs film was obtained as a function of film thickness at growth temperatures of 420, 445 and 477°C. In the early stages of strain relaxation, it was found that evolution of the residual strain and crystal quality was dependent on the growth temperature. In order to discuss this observation quantitatively, the strain relaxation model was proposed based on the DodsonTsao kinetic model, and its validity was demonstrated by good agreement with the experimental residual strain. Additionally, rate coefficients reflecting dislocation motions during strain relaxation were obtained as a function of growth temperature and strain relaxation was discussed in terms of the thermally active dislocation motion. © 2010 Elsevier B.V. All rights reserved.
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Bouzazi B., Lee J., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Japanese Journal of Applied Physics 50 ( 5 PART 1 ) 2011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
The origin of a N-related recombination center (E1), at around 0.33 eV below the conduction band minimum (CBM) of chemical beam epitaxy (CBE) grown GaAsN, is discussed based on effect of H implantation and dependence of E1 density to As flow rate (TDMAAs). After H implantation, E1 disappears completely whereas two new defects are recorded. The first one (HP1) is a hole trap at around 0.11 eV above the valence band minimum, similar to a N-related hole trap in unintentionally doped p-type GaAsN grown by CBE and expected to be N-H-V Ga . The second level (EP1) is an electron trap at around 0.41 eV from CBM, identical to EL5 native defect in GaAs and expected to be V Ga -As i or As Ga -V Ga . The atomic structure of E1 is discussed from that of HP1 and EP1 and it is expected to be the split interstitial (N-As) As . This expectation is supported by the peaking behavior of E1 density with As source flow rate. © 2011 The Japan Society of Applied Physics.
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Shallow carrier trap levels in GaAsN investigated by photoluminescence 査読あり
Inagaki M., Suzuki H., Suzuki A., Mutaguchi K., Fukuyama A., Kojima N., Ohshita Y., Yamagichi M.
Japanese Journal of Applied Physics 50 ( 4 PART 2 ) 04DP14 - 04DP14-4 2011年4月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Japanese Journal of Applied Physics
Shallow carrier trap levels in GaAs 1-x N x (0:0010 ≤ x ≤ 0:0038) were investigated by photoluminescence (PL) and photoreflectance (PR) ranging from 4.2 to 300 K. The band gap energies of the GaAsN were clearly determined in the whole temperature range by the PR fitting analysis. It is clarified by peak decomposing that there were three emission peaks in the near-band-edge PL spectra of GaAsN. One of them was originated from band-to-band transition. The energies of two emission peaks were located at approximately 6 and 17meV below the band edge. The existence of these peaks is evidence of carrier localization at the near-band-edge. The intensity ratio of the peak at the low energy side to other peaks increases with increasing N composition. This behavior is similar to the degradation of electrical properties. © 2011 The Japan Society of Applied Physics.
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Bouzazi B., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Physica B: Condensed Matter 406 ( 5 ) 1070 - 1075 2011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：Physica B: Condensed Matter
A nitrogen-related electron trap (E1), located approximately 0.33 eV from the conduction band minimum of GaAsN grown by chemical beam epitaxy, was confirmed by investigating the dependence of its density with N concentration. This level exhibits a high capture cross section compared with that of native defects in GaAs. Its density increases significantly with N concentration, persists following post-thermal annealing, and was found to be quasi-uniformly distributed. These results indicate that E1 is a stable defect that is formed during growth to compensate for the tensile strain caused by N. Furthermore, E1 was confirmed to act as a recombination center by comparing its activation energy with that of the recombination current in the depletion region of the alloy. However, this technique cannot characterize the electron-hole (eh) recombination process. For that, double carrier pulse deep level transient spectroscopy is used to confirm the non-radiative eh recombination process through E1, to estimate the capture cross section of holes, and to evaluate the energy of multi-phonon emission. Furthermore, a configuration coordinate diagram is modeled based on the physical parameters of E1. © 2010 Elsevier B.V. All rights reserved.
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Novel material for super high efficiency multi-junction solar cells
Ohshita Y., Suzuki H., Kojima N., Tanaka T., Honda T., Inagaki M., Yamaguchi M.
Journal of Crystal Growth 318 ( 1 ) 328 - 331 2011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：Journal of Crystal Growth
For realizing a future four-junction solar cell InGaP/GaAs/InGaAsN/Ge with high conversion efficiency of over 40% (AM1.5G), we are developing the chemical beam epitaxy (CBE) technology to grow high-quality InGaAsN. This diluted nitride will be used as a third cell material, because it can be grown on Ge with lattice matching and a 1.0 eV band gap. However, due to the small amount of N incorporated into the GaAs (or InGaAs) crystal, the diffusion length becomes too short to fabricate the tandem solar cells with the high performance we expect. The films in the CBE process are grown using organic gas molecules as sources under high vacuum conditions (10 -2 Pa). Because of the ultra-low pressure, the reactions between the source-gas molecules in the gas phase are suppressed and the reactions only occur on the growing surface. This allows the use of active source gases that decompose at low temperatures. The CBE growth technique produces high quality GaAsN. The lower TEGa flow rate is one of the most important factors to obtain low residual impurities, higher mobility (Hall hole mobility), and longer lifetime (Photoluminescence lifetime). © 2010 Elsevier B.V. All rights reserved.
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Bouzazi B., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Physica Status Solidi (C) Current Topics in Solid State Physics 8 ( 2 ) 616 - 618 2011年2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：Physica Status Solidi (C) Current Topics in Solid State Physics
The relationship between a nitrogen (N)-related hole trap and the density of ionized acceptors (N A ) in p-type GaAsN grown by chemical beam epitaxy (CBE) is investigated using deep level transient spectroscopy and temperature dependence of the junction capacitance. As results, N A at room temperature is found to be in linear dependence with N concentration. Further, a N-dependent sigmoid increase of the junction capacitance in a specific range of temperature, between 70 and 100 K, is observed. Such behavior is explained by the thermal ionization of a N-related like-acceptor hole trap; located at approximately 0.15 eV above the valence band maximum of GaAsN. The density of this trap determines in great part the magnitude of N A and causes the high background doping in unintentionally doped p-type GaAsN grown by CBE. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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N incorporation and optical properties of GaAsN epilayers on (3 1 1)A/B GaAs substrates 査読あり
Han X., Suzuki H., Lee J., Kojima N., Ohshita Y., Yamaguchi M.
Journal of Physics D: Applied Physics 44 ( 1 ) 2011年1月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Journal of Physics D: Applied Physics
We compared the N incorporation and optical emission in GaAsN epilayers grown on (3 1 1)A/B and (1 0 0) GaAs substrates using a chemical beam expitaxy system. Over the growth-temperature range 420 -460 °C, N composition was enhanced 2-3 times for the epitaxial growth following [3 1 1]B orientation, but reduced in the [3 1 1] A direction. Both (3 1 1) A and B substrates are effective to weaken the photoluminescence emission from the deep levels as compared with the (1 0 0) plane. The deep-level emission can be further suppressed for all substrates by increasing the growth temperature and/or performing postgrowth annealing. However, in contrast to the continuous increase in total emission intensities of (3 1 1)B sample, a decreasing tendency was recorded for (3 1 1)A with the rise in growth temperature. The optimum growth temperature and annealing conditions for better crystal quality were found to depend on the growth orientation and surface polarity. These results present a potential approach to improving the N incorporation efficiency in Ga(In)AsN materials through adopting high-index substrates such as (3 1 1)B. © 2011 IOP Publishing Ltd.
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A recombination center in p-type GaAsN grown by chemical beam epitaxy
Bouzazi B., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Solar Energy Materials and Solar Cells 95 ( 1 ) 281 - 283 2011年1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：Solar Energy Materials and Solar Cells
The double carrier pulse deep level transient spectroscopy (DLTS) technique is used to characterize recombination centers in p-type GaAsN grown by chemical beam epitaxy. The DLTS peak height of a shallow hole trap H1, at 0.052 eV from the valence band edge of GaAsN, decreases by the injection of both majority and minority carriers for various values of voltage and duration of the second pulse. Although the trap is shallow, its capture cross section is relatively large to capture electrons and holes. The decrease in the number of traps is explained by the electronhole recombination process. This confirms, for the first time, that H1 is a recombination center in p-type GaAsN. © 2010 Elsevier B.V. All rights reserved.
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Origin of near-band-edge photoluminescence of GaAsN
Inagaki M., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2062 - 2065 2010年12月
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：Conference Record of the IEEE Photovoltaic Specialists Conference
The emission processes at high energy edge of PL spectra of GaAsN are clarified by the temperature dependence photoluminescence (PL) spectra and time resolved PL spectra. The PL spectra and TR-PL spectra of GaAsN are deconvoluted by three Gaussian functions (P1, P2 and P3 from high energy side). There are three emission processes at high energy edge of PL spectra of GaAsN. The energies of P2 and P3 are ∼6 meV and ∼17 meV lower than that of P1. The integrated intensity of P1 increases with increasing temperature from 4.2K to 50K, while those of the other peaks decrease. From these results, following possibility are suggested: (i) the origin of P1 is band to band transition, (ii) the origin of P2 is caused by free exciton or shallow donor related recombination, and (iii) P3 originate from donor-acceptor pair emission or overlapping of emission which comes from a number of localized states. © 2010 IEEE.
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Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2117 - 2119 2010年12月
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：Conference Record of the IEEE Photovoltaic Specialists Conference
Structural difference between high and low N induced scattering center (SC N ) concentration GaAsN films grown on GaAs substrates has been investigated by X-ray reciprocal space mapping technique. Difference has been observed in diffuse scattering around GaAsN 004 and GaAs 004 Bragg peak, which is attributed to misfit dislocation at the interface of GaAsN/GaAs. With decreasing SC N , intensity of diffuse scattering increases. These results indicate that SC N prevent the generation and/or gliding of misfit dislocations. © 2010 IEEE.
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Han X., Suzuki H., Lee J., Inagaki M., Kojima N., Ohshita Y., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2050 - 2052 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
GaAsN expilayers were grown on (100), (211)A/B, (311)A/B and (511)A/B GaAs substrates at different temperatures by using a chemical beam epitaxy system. Results of high resolution X-ray diffraction, low- and room-temperature photoluminescence (PL) measurements indicated that dangling bond status (polarity and density) on the growing surface has significant influence on the final N composition and the PL emission behavior in GaAsN epilayers. As compared with the (100) substrate, (n11)B substrates tended to enhance the N incorporation, whereas (n11)A dramatically reduced it. At the growth temperature of 460°C, N composition in (211)B GaAsN is almost 10 times higher than that in (211)A. The extent of enhancement (or reduction) of N incorporation was found to depend on the relative amount of (111)B (or (111)A) component on the growth surface. PL spectra of samples grown at 460oC suggested that optical properties could be improved by most of the adopted (n11) substrates. Especially, efficient N incorporation in GaAsN epilayers can be achieved on (211)B and (311)B substrates while keeping improved crystal quality. © 2010 IEEE.