論文 - 鈴木 秀俊
-
Koto H., Kawano M., Suzuki H.
Japanese Journal of Applied Physics Part 1 Regular Papers and Short Notes and Review Papers 64 ( 4 ) 2025年4月
担当区分：最終著者, 責任著者 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 Part 1 Regular Papers and Short Notes and Review Papers
In this study, to control the N distribution in GaAsN films, GaAsN/GaAs superlattice (SL)-structure films were grown by repeating one cycle of the GaAsN atomic layer growth sequence and n (0-9) cycles of the GaAs growth sequence using atomic layer epitaxy. The effects of n on the incorporation of N atoms into the GaAsN layer and the detailed N distribution in the film were investigated by considering the lattice constants of the GaAsN/GaAs SL and SL periods, as evaluated by X-ray diffraction. The formation of the SL structures was confirmed, although the SL periods deviated slightly from the designed values. The SL periods were not singular for the films and the direction of the SL period was slightly tilted (∼0.2°) from the growth direction. This indicates the existence of at least two regions with different tilt directions and periods in the film.
-
T. Harada,S. Harada, H. Suzuki, S. Endo, A. Ogura, M. Imaizumi, T. Ikari, A. Fukuyama
Journal of Physics D: Applied Physics 58 ( 11 ) 2025年3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
To reduce fluctuations in the performance of lattice-mismatched solar cells within a wafer, it is necessary to characterize and quantify the effect of misfit dislocations, caused by strain relaxation, on the performance of a solar cell. To this end, the relationship between the preferential glide planes (GPs) and the carrier generation-recombination process in InGaAs solar cells with low (LowV) and high (HighV) open-circuit voltages has been investigated in this study. The GPs of the β dislocations in the HighV cells were uniformly controlled in the wafer plane. However, the LowV cells contained a mixture of two in-plane regions, in which the GPs of the β dislocations were controlled by the surface atomic steps during their growth on a vicinal substrate (LowV-sub region) or by the InGaP ordering effect (LowV-ord region). The results of the microwave photoconductivity decay method and our newly-developed laser heterodyne photothermal displacement method suggested that the photoexcited carrier concentration was low in the LowV-ord region. A photoluminescence measurement as a function of temperature further revealed that indium fluctuations occurred due to the presence of the GPs of the β dislocation. The LowV cells exhibited high indium composition and reduced bandgap. Thus, a small photoexcited carrier concentration and reduced bandgap energy decreased the difference between the quasi-Fermi levels of electrons and holes, resulting in a small VOC. The photovoltaic performance could be determined by the density of the threading dislocations and the corresponding fluctuations in the indium composition owing to the different GPs of the β dislocations.
-
M. Kawano, T. Haraguchi, H. Suzuki
Journal of Crystal Growth 649 2025年1月
担当区分：最終著者, 責任著者 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
The effects of nitrogen (N) distribution on the electrical properties of GaAsN films were evaluated by intentionally changing the N distribution using atomic layer epitaxy (ALE) and post-annealing. The N distribution was controlled in the growth direction by growing superlattice (SL) thin films repeatedly growing 1 GaAsN layer and 0, 3, and 5 layers of GaAs by ALE. These films were referred to as (1:0), (1:3), and (1:5), respectively. To change the N distribution in the same thin film, N atoms were diffused by post-annealing. Changes in N distribution were evaluated by X-ray diffraction as changes in GaAsN superstructure. N atoms diffused from GaAsN layers to the adjacent layers in (1:3) films annealed above 750 °C, while they remained stable in those of (1:5) films annealed at temperatures up to 850 °C. The carrier mobility of both films increased monotonically with the annealing temperature. The concentration of ionized scattering centers decreased significantly in films annealed at 650 °C (independent of their N distributions) owing to the elimination of donor-type defects by annealing. Contrarily, the concentrations of N-induced scattering centers in (1:5) films annealed below 900 °C were similar, while those in (1:3) films annealed above 750 °C decreased significantly, in agreement with the N-atom diffusion behavior of GaAsN layers. Thus, N-distribution homogenization can be related to the reduction of N-induced scattering centers.
-
格子不整合系InGaAs 太陽電池における転位すべり面の向きが光励起キャリアの再結合に与える影響
原田 尚吾, 原田 知季, 鈴木 秀俊, 小倉 暁雄, 碇 哲雄, 福山 敦彦
宮崎大学工学部紀要 53 57 - 64 2024年10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） 出版者・発行元：宮崎大学工学部
Lattice-mismatched solar cells are known to have high conversion efficiency. However, their open-circuit voltages (VOC) are not uniformly distributed within a wafer due to the preferential glide plane of β dislocations. Furthermore, the effect of dislocations on the carrier recombination process is still under discussion. We investigated two types of InGaAs solar cells with the InGaP step-graded buffer layers grown on the vicinal GaAs substrate. The first cell showed a high VOC (HighV), and the preferential glide plane of β dislocations was well controlled using the vicinal substrate. The second cell had a low VOC (LowV), where the preferential glide planes of β dislocations were nonuniformly distributed within the cell due to the InGaP ordering effect. In this study, laser heterodyne photothermal displacement mappings, microwave photoconductivity decay mappings, and photoluminescence measurements were performed to discuss carrier recombination properties. In the HighV cell, almost uniform signal distributions were observed. On the other hand, the observed signals in the LowV cell were nonuniformly distributed. We also found that the obtained results of nonuniformity correspond to the distribution of preferential glide planes of β dislocations. These results indicate that the VOC reduction strongly depends on the direction of the preferential glide plane of β dislocations.
DOI： 10.34481/0002000816
-
逆格子マッピング測定を用いた、格子不整合InGaAs太陽電池の転位滑り面の面内分布異方性の観察
鈴木 秀俊
九州シンクロトロン光研究センター利用報告書2023年度 2024年10月
担当区分：筆頭著者 記述言語：日本語 掲載種別：研究論文（大学，研究機関等紀要）
-
Harada S., Suzuki H., Ogura A., Imaizumi M., Ikari T., Fukuyama A.
28th Microoptics Conference Moc 2023 2023年
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：28th Microoptics Conference Moc 2023
We investigated the relationships between the distribution of dislocation glide planes and carrier recombination properties in InGaAs solar cells with different open-circuit voltage (VOC) using microwave photoconductivity decay and photoluminescence measurements. The results showed the low VOC was due to the recombination of the photoexcited carriers with the dislocation-related defect.
-
Ogura A., Nogawa S., Kawano M., Minematsu R., Suzuki H.
Applied Physics Express 14 011001 2020年12月
記述言語：英語 掲載種別：研究論文（学術雑誌）
By using synchrotron X-ray diffraction, we investigated the in-plane distribution of preferential glide planes in a metamorphic InGaAs solar cell with a relatively low open-circuit voltage (Voc) compared to other cells fabricated on the same wafer. The reciprocal-space maps revealed that the low-Voc cell contains several domains with different preferential glide planes of β dislocations. Since fluctuations of the average β-glide plane have not been observed for high-Voc cells, the observed inhomogeneous distribution should be related to the Voc degradation. Understanding preferential glide-plane changes within a cell can help to improve the uniformity of cell properties over the whole wafer.
-
Ogura A., Yi W., Chen J., Suzuki H., Imaizumi M.
Journal of Electronic Materials 49 ( 9 ) 5219 - 5225 2020年9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 Electronic Materials
© 2020, The Minerals, Metals & Materials Society. Epitaxial growth of lattice-mismatched materials is useful for solar cells, but lattice dislocations must be controlled for best device performance. It has been shown that metamorphic growth enables fabrication of InGaAs p–n junctions with good performances on GaAs substrates due to the insertion of buffer layers. Here, we investigate misfit and threading dislocations inside the step-graded InGaP buffer layers of a single-junction InGaAs solar cell by cathodoluminescence microscopy. Prior to measurement, the device edges were polished at various angles (less than 10° with respect to the substrate surface). By using this technique, cross sections of very thin layers can be directly imaged with a resolution that allows us to observe misfit and threading dislocations. In the present device, the densities of the two types of dark lines depend on the position in the buffer structure. In particular, near the InGaAs base layer, the density of the dark lines extending in the [110] direction is higher than that of the dark lines extending in the [1-10] direction. We believe that this difference in the dark line density is related to the surface morphology.
-
Suzuki H., Ishikawa F., Sasaki T., Takahasi M.
Applied Physics Express 13 ( 5 ) 2020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：Applied Physics Express
© 2020 The Japan Society of Applied Physics. We carry out real-time in situ synchrotron X-ray diffraction on the growth of GaN and AlN on SiC(0001) substrate by molecular beam epitaxy. At the initial growth stage of GaN/SiC or AlN/SiC heterostructure, the epitaxial overlayer develops affected by defects with the strain interaction between SiC, eventually showing characteristic lattice deformations. GaN was almost relaxed at the initial stage, showing the transition of the growth mode from 3D to 2D at around 4 nm. In contrast, AlN coherently grow on SiC(0001) at the initial stage for 13 nm concomitantly showing lattice deformation with the beneath SiC, subsequently showing gradual lattice relaxation.
-
Kawano M., Minematsu R., Haraguchi T., Fukuyama A., Suzuki H.
Japanese Journal of Applied Physics 59 ( SG ) SGGF10 2020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
© 2020 The Japan Society of Applied Physics. GaAsN films with different N distributions have been grown using the atomic layer epitaxy method to evaluate the effects of N distribution on the electrical properties of GaAsN. Three films, which had the same N composition with different N distribution were fabricated by alternate stack of GaAsN 1 monolayer (ML) and GaAs (0, 3, 5) ML. According to the X-ray diffraction measurement, periodicity and small N interdiffusion between GaAs and GaAsN layers in grown GaAsN films were confirmed. Thus, N distribution in the films were successfully modified in the order of a few unit lattice. Contribution of each scattering mechanisms on carrier mobility and densities of scattering centers in grown GaAsN films were evaluated. Compared with the film with 0 ML of GaAs, the density of N induced scattering center decreased with insertion of GaAs 3 ML between GaAsN 1 ML. It again increased the film with insertion of GaAs 5 ML. These results suggest that controlling N distribution intentionally not only degraded but also improved the electrical properties of GaAsN films.
-
Ogura A., Suzuki H., Imaizumi M.
Journal of Crystal Growth 533 2020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
© 2019 Elsevier B.V. Metamorphic growth of light absorber layers of solar cells introduces misfit dislocations due to strain relaxation, and their influences on the solar cell performance need to be characterized. In this work, we correlate the asymmetry of relaxation probabilities via different glide planes (which results in a tilt of the epilayer) with the open-circuit voltages (Voc) of several metamorphic InGaAs single junction solar cells. The devices contain graded InGaP buffer layers and are grown on a GaAs 001 wafer with a small miscut towards the 100 direction. We observe an inhomogeneous distribution of the solar cells’ Voc within the wafer and are able to correlate the Voc fluctuation to a difference in the asymmetry of the glide plane distributions of α and β dislocations. In the case of solar cells exhibiting a high Voc, the glide planes of both α and β dislocations are controlled by the surface orientation. In the case of low-Voc samples, the glide planes of the β dislocations are controlled by the ordering of InGaP, while those of the α dislocations are still controlled by the surface orientation.
-
Ogura A., Nogawa S., Kawano M., Minematsu R., Kubo K., Imaizumi M., Suzuki H.
Applied Physics Express 14 ( 1 ) 2020年
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
By using synchrotron X-ray diffraction, we investigated the in-plane distribution of preferential glide planes in a metamorphic InGaAs solar cell with a relatively low open-circuit voltage (V oc) compared to other cells fabricated on the same wafer. The reciprocal-space maps revealed that the low-V oc cell contains several domains with different preferential glide planes of β dislocations. Since fluctuations of the average β-glide plane have not been observed for high-V oc cells, the observed inhomogeneous distribution should be related to the V oc degradation. Understanding preferential glide-plane changes within a cell can help to improve the uniformity of cell properties over the whole wafer.
-
Inhomogenious distribution of misfit dislocations in metamorphic InGaAs solar cells
Shota Nogawa, Akio Ogura, Masahiro Kawano, Koushirou Kubo, Mitsuru Imaizumi, and Hidetoshi Suzuki
Abstract of the 19th international conference on solid films and surfaces 2019年10月
記述言語：英語 掲載種別：研究論文（研究会，シンポジウム資料等）
-
Growth and Evaluation of GaAsN Films With Different N Distribution Grown by Atomic Layer Epitaxy
M. Kawano, R. Minematsu, T. Haraguchi, A. Fukuyama, H. Suzuki
Abstract of solid state devices and materials 2019 C-5-04 2019年9月
記述言語：英語 掲載種別：研究論文（研究会，シンポジウム資料等）
-
その場X線回折測定を用いた GaAs(001)基板上InGaAs成長におけるIn偏析の解析 査読あり
鈴木 秀俊, 佐々木 拓生, 高橋 正光, 大下 祥雄
SPring-8/SACLA利用研究成果集 7 ( 2 ) 2019年8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）
分子線エピタキシー法を用いた GaAs(001) 基板上への InGaAs 薄膜成長中のIn偏析過程の解明を目指し、放射光を用いたX線回折法を用いてリアルタイム測定を行った。回折強度計算と実験結果との比較から、成長中の膜中の In 分布の変化を算出し、各時点での偏析係数を見積もった。成長速度が早い場合は (0.20, 0.27 ML/s)、一つの偏析係数で計算結果と実験結果が一致したが、成長速度が遅い場合 (0.10 ML/s) では一つの偏析係数で説明することが不可能であった。この結果は、特に成長速度が遅い場合において、これまでの偏析モデルを修正する必要を示唆している。
-
Ogura A., Tanikawa T., Takamoto T., Oshima R., Suzuki H., Imaizumi M., Sugaya T.
Conference Record of the IEEE Photovoltaic Specialists Conference 273 - 276 2019年6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
© 2019 IEEE. Lattice-mismatched materials enable growth of IIIV multi junction solar cells with band-gap combinations that are closer to the theoretical optimum than those of conventional material combinations. In order to improve material quality and hence conversion efficiency, it is important to reduce threading dislocations by employing graded buffer layers (GBLs) between subcells with different lattice constants. We have to understand how threading dislocations are formed from misfit dislocations, which are generated at the heterointerfaces in the GBL to relax strain. In this report, misfit dislocations inside the GBL of inverted metamorphic (IMM) single-junction InGaAs solar cells are directly observed by using two-photon excitation photoluminescence. A clear depth dependence of the dislocations inside the GBL can be confirmed. The results indicate that the strain relaxation processes in solar cells with high open-circuit voltages are distinctly different from those in solar cells with low open-circuit voltages.
-
Fukuyama A., Tategami S., Takauchi K., Matsuda N., Nakamura T., Suzuki H., Nishioka K., Ikari T.
2018 IEEE 7th World Conference on Photovoltaic Energy Conversion, WCPEC 2018 - A Joint Conference of 45th IEEE PVSC, 28th PVSEC and 34th EU PVSEC 1792 - 1795 2018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：2018 IEEE 7th World Conference on Photovoltaic Energy Conversion, WCPEC 2018 - A Joint Conference of 45th IEEE PVSC, 28th PVSEC and 34th EU PVSEC
© 2018 IEEE. Hall mobility measurements of {n}- and p-type Si substrate under the concentrated sunlight irradiation were carried out to discuss the effect of large amount of carrier generation. The Hall mobility decreased Linearly with increasing the sunlight concentration. It was also found that these decrease could prevent by using a sample with high doping concentration. From the comparison with the calculation, we concluded that the reduction of Hall mobility was due to increase of the photo-generated carriers (both hole and electron). Calculation of Hall mobility as a function of impurity doping concentration demonstrated that a suitable doping concentration for solar cell use was considered to be 10{16}\mathrm {c}\mathrm {m}{-3} in both {n}- and p-type Si substrate from viewpoint of Hall mobility under 16-suns concentrated irradiation.
-
Suzuki Hidetoshi, Sasaki Takuo, Takahasi Masamitu, Ohshita Yoshio, Kojima Nobuaki, Kamiya Itaru, Fukuyama Atsuhiko, Ikari Tetsuo, Yamaguchi Masafumi
Jpn. J. Appl. Phys. 56 ( 8 ) 2017年7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：Institute of Physics
The effect of substrate orientation on strain relaxation mechanisms of an InGaAs layer grown on vicinal GaAs substrates was investigated by in situ X-ray diffraction (XRD). The crystallographic tilt and indium segregation in the InGaAs layer were altered depending on the miscut direction and angle. In the case of the substrate tilted 6° toward the [110] direction, one type of misfit dislocations was formed preferentially rather than other types, especially in the rapid relaxation phase. While in the case of the substrate tilted 6° toward the [Formula: see text] direction, no anisotropies during relaxation were observed. The present finding indicates that the appropriate use of vicinal substrates may lead to a novel method of improving the crystal quality of heterolayers.
-
Fukuyama Atsuhiko, Matsuochi Kouki, Nakamura Tsubasa, Takeda Hideaki, Toprasertpong Kasidit, Sugiyama Masakazu, Nakano Yoshiaki, Suzuki Hidetoshi, Ikari Tetsuo
Jpn. J. Appl. Phys. 56 ( 8 ) 2017年7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：Institute of Physics
To improve the superlattice (SL) solar cell performance, we carried out an accurate estimation of transition energies and miniband widths and focused on understanding of the optical properties of the SL structure using piezoelectric photothermal (PPT), photoreflectance (PR), and photoluminescence (PL) methods. Solar cell structure samples with different barrier thicknesses from 2.0 to 7.8 nm in quantum wells were prepared. From the PR and theoretical calculation, the formation of a miniband was confirmed. The PL peak showed a redshift and a decrease in signal intensity with decreasing barrier thickness, which were explained by carrier separation as a consequence of electron transportation through the miniband without recombination. The PPT signal intensities of the SL were still large even for the 2.0-nm-barrier-thickness sample. It is conceivable that the multiple-phonon emission during carrier transport through the miniband was detected. The usefulness of multidimensional investigation by using the above three methods is clearly demonstrated.
-
Material conversion of GaAs nanowires 査読あり
Nishioka K., Suzuki H., Sakai K., Ishikawa F.
Physica Status Solidi (B) Basic Research 254 ( 2 ) 2017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：Physica Status Solidi (B) Basic Research
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim We investigate material conversion of compound semiconductor GaAs nanowires to extend their functions. By heating the GaAs nanowires in indium melt, the indium was introduced into the GaAs nanowire, converting the nanowires to be InGaAs compounds. The further heating treatment in N 2 ambient progresses the diffusion of Si element from the substrate, eventually forming the indium–silicide compound nanowires. The results suggest the conversion technique possibly extend the functions of the nanowire system by the exchange, introduction, or integrations of various materials.
-
Sakai K., Takeshita H., Haraguchi T., Suzuki H., Ohashi F., Kume T., Fukuyama A., Nonomura S., Ikari T.
Thin Solid Films 621 32 - 35 2017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：Thin Solid Films
© 2016 Elsevier B.V. By means of high-resolution transmission electron microscopy (HR-TEM) observations, and energy dispersive X-ray analyses performed with a scanning TEM (STEM-EDX), we evaluated the residual Na contents and the induced crystal strains in type-II Si clathrate films grown on a Si substrate and treated with iodine for Na elimination. Cross-sectional TEM and STEM-EDX observations verified the formation of the type-II Si clathrate thin film on the Si substrate. The guest-free (without any Na inclusion) clathrate crystal was obtained by iodine (I 2 ) treatment for more than 3 cycles. The resulting films were polycrystalline. No buffer layer was observed at the boundary of the Si clathrate crystal film and the substrate, suggesting a chemical bonding between them. The crystalline strains defined here by the deviation of the d value were within 3.5%. These findings might allow us to fabricate epitaxial Si clathrate films on Si substrates.
-
Fukuyama A., Matsuochi K., Nakamura T., Takeda H., Suzuki H., Toprasertpong K., Sugiyama M., Nakano Y., Ikari T.
Nanotechnology Materials and Devices Conference, NMDC 2016 - Conference Proceedings 2016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：Nanotechnology Materials and Devices Conference, NMDC 2016 - Conference Proceedings
© 2016 IEEE. To investigate the miniband and carrier transport properties in the superlattice structure embedded in the p-i-n GaAs solar cells, photoreflectance, photoluminescence, and photothermal spectroscopies were adopted. Two critical energies corresponding to the energy differences between mini-Brillouin zone edges were estimated for thinnest quantum barrier thickness sample by PR. From the PPT and PL, only broad peaks corresponding to the quantum levels were observed and we concluded that a built-in electric field inhibited the formation of miniband.
-
Crystal growth of GaAs on high indexed Si substrates for multi-junction solar cells
Harada I., Suzuki H., Ikari T., Fukuyama A.
Conference Record of the IEEE Photovoltaic Specialists Conference 2016-November 1947 - 1949 2016年11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
© 2016 IEEE. The effects of surface orientation of Si surface on crystal quality and surface morphology of GaAs layer grown on the Si substrate was investigated. Si (001), (113) and (114) wafers were used as substrates, and GaAs crystal was deposited on the substrate using molecular beam epitaxy. Before growth, the substrates were thermally cleaned in an ultra high vacuum chamber using an infrared heating unit. Crystal quality and surface roughness of the GaAs/Si (113) was better than those of other samples. This suggested that crystal quality of GaAs/Si could be improved using the Si (113) substrate.
-
Thin film of guest-free type-II silicon clathrate on Si(111) wafer 査読あり
Tetsuji Kume, Fumitaka Ohashi, Kentaro Sakai, Atsuhiko Fukuyama, Motoharu Imai, HaruhikoUdono, Takayuki Ban, Hitoe Habuchi, Hidetoshi Suzuki, Tetsuo Ikari, Shigeo Sasaki, Shuichi Nonomura
Thin Solid Films 609 30 - 34 2016年4月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
Real-time observation of rotational twin formation during molecular-beam epitaxial growth of GaAs on Si (111) by x-ray diffraction 査読あり
Hidetoshi Suzuki, Yuka Nakata, Masamitu Takahasi, Kazuma Ikeda, Yoshio Ohshita, Osamu Morohara, Hirotaka Geka, Yoshitaka Moriyasu
AIP Advances 6 035303-1 - 035303-6 2016年3月
記述言語：英語 掲載種別：研究論文（学術雑誌）
DOI： 10.1063/1.4943511
-
Nakamura T., Matsuochi K., Suzuki H., Ikari T., Toprasertpong K., Sugiyama M., Nakano Y., Fukuyama A.
Energy Procedia 102 121 - 125 2016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：Energy Procedia
© 2016 The Authors. We investigated the effect of built-in electric field on miniband formation and carrier nonradiative recombination in a superlattice structure by using photoreflectance (PR) and photoluminescence (PL) spectroscopy for a strain-balanced InGaAs/GaAsP superlattice inserted in p-i-n GaAs solar cell and n-n GaAs structures. Two critical energies were obtained in the PR spectra, which corresponded to the energy differences between the Γ and π points in the mini-Brillouin zone of the first electron level and the first heavy hole level. The obtained miniband widths of both samples were same, which were smaller than the calculated values by using a flat-band structure model without a built-in electric field. From these results, it was deduced that the built-in electric field does not affect the miniband width. The PL signal intensity of the p-i-n structure samples did not change, whereas that of the n-n structure samples decreased with decreasing barrier thickness. We concluded that the radiative recombination probability decreases and the non-radiative recombination probability increases due to miniband formation.
-
新規Ge原料 t-C4H9GeH3のSiもしくはGaAs基板上における表面反応過程
河野 将大, 山内 俊浩, 石川 真人, 須藤 弘, 町田 英明, 大下 祥雄, 鈴木 秀俊
表面科学学術講演会要旨集 36 ( 0 ) 2016年
記述言語：日本語 掲載種別：研究論文（研究会，シンポジウム資料等） 出版者・発行元：公益社団法人 日本表面科学会
GaAs/Si構造は、多接合型太陽電池等への応用が期待されている。本構造の格子定数差等に起因する欠陥の低減手法として、Geバッファ層が提案されている。近年、安全で取扱いが容易な新しいGe原料としてt-C<sub>4</sub>H<sub>9</sub>GeH<sub>3</sub>（tBGe）が提案されているが、各種基板上での反応過程など不明な点が多い。本研究では、Si又はGaAs基板上におけるtBGeの表面反応と成長初期過程を明らかにすることを目的とした。
-
Control of hydrogen and carbon impurity inclusion during the growth of GaAsN thin film by atomic layer epitaxy 査読あり
Yuki Yokoyama, Atsuhiko Fukuyama, Tomohiro Haraguchi, Toshihiro Yamauchi, Tetsuo Ikari, Hidetoshi Suzuki
Japanese Journal of Applied Physics 55 01AC06-1 - 01AC06-4 2015年12月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
Shimomura K., Suzuki H., Sasaki T., Takahasi M., Ohshita Y., Kamiya I.
Journal of Applied Physics 118 ( 18 ) 2015年11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
© 2015 AIP Publishing LLC. Direct measurements on the growth of InAs quantum dots (QDs) and various cap layers during molecular beam epitaxy are performed by in situ X-ray diffraction (XRD). The evolution of strain induced both in the QDs and cap layers during capping is discussed based on the XRD intensity transients obtained at various lattice constants. Transients with different features are observed from those obtained during InGaAs and GaAs capping. The difference observed is attributed to In-Ga intermixing between the QDs and the cap layer under limited supply of In. Photoluminescence (PL) wavelength can be tuned by controlling the intermixing, which affects both the strain induced in the QDs and the barrier heights. The PL wavelength also varies with the cap layer thickness. A large redshift occurs by reducing the cap thickness. The in situ XRD observation reveals that this is a result of reduced strain. We demonstrate how such information about strain can be applied for designing and preparing novel device structures.
DOI： 10.1063/1.4935456
-
In situ three-dimensional X-ray reciprocal-space mapping of InGaAs multilayer structures grown on GaAs(001) by MBE 査読あり
Takuo Sasaki, Masamitu Takahasi, Hidetoshi Suzuki, Yoshio Ohshita, Masafumi Yamaguchi
Journal of Crystal Growth 425 13 - 15 2015年9月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
Ikeda K., Ohshita Y., Tanaka T., Honda T., Inagaki M., Demizu K., Kojima N., Suzuki H., Machida H., Sudoh H., Yamaguchi M.
Japanese Journal of Applied Physics 54 ( 4 ) 2015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
© 2015 The Japan Society of Applied Physics. The formation mechanism of N-H-related defects in GaAsN grown by chemical beam epitaxy (CBE) is studied on the basis of the isotope effects on the local vibration modes (LVMs) originating from N-H. When deuterated monomethylhydrazine (MMHy) is used as the N source, LVM signals from the nitrogen-deuterium bond (N- D) are obtained. However, there are still N-H peaks in the IR absorption spectra, which have intensities similar to those of N-D peaks. When the film is grown with deuterated triethylgallium (TEGa), there are no N-D peaks. The peak intensity at 2952 cm -1 increases with increasing tris(dimethylamino)arsenic (TDMAAs) flow rate, and that at 3098 cm -1 is almost constant regardless of the flow rate. These results indicate that H atoms in the N-H-related defects originate from H directly bonded to N in MMHy and CH 3 in MMHy and/or H in TDMAAs, not from TEGa.
-
Effect of number of stack on the thermal escape and non-radiative and radiative recombinations of photoexcited carriers in strain-balanced InGaAs/GaAsP multiple quantum-well-inserted solar cells 査読あり
Taketo Aihara, Atsuhiko Fukuyama, Hidetoshi Suzuki, Hiromasa Fujii, Masakazu Sugiyama, Yoshiaki Nakano, Tetsuo Ikari
Journal of Applied Physics 117 084307 2015年2月
記述言語：英語 掲載種別：研究論文（学術雑誌）
DOI： 10.1063/1.4913593
-
Zinc-blende and wurtzite phase separation in catalyst-free molecular beam epitaxy vapor–liquid–solid-grown Si-doped GaAs nanowires on a Si(111) substrate induced by Si doping 査読あり
Akio Suzuki, Atsuhiko Fukuyama, Hidetoshi Suzuki, Kentaro Sakai, Ji-Hyun Paek, Masahito Yamaguchi, Tetsuo Ikari
Japanese Journal of Applied Physics 54 ( 3 ) 035001 2015年2月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
大西 修, 境 健太郎, 鈴木 秀俊, 森田 翔
日本機械学会九州支部講演論文集 2015 ( 0 ) 327 - 328 2015年
-
Fukuyama A., Ding W., Morioka G., Suzuki A., Suzuki H., Yamaguchi M., Ikari T.
2014 IEEE 40th Photovoltaic Specialist Conference, PVSC 2014 1148 - 1151 2014年10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：2014 IEEE 40th Photovoltaic Specialist Conference, PVSC 2014
© 2014 IEEE. To investigate the microstructure of nitrogen-induced localized state (E N ) that perturbs the conduction band of GaAs host material, we adopted the photoreflectance measurements to chemical-beam-epitaxy grown GaAsN thin films. We measured both two split subbands to estimate correct values of E N . It was clearly seen that estimated E N decreased with increasing nitrogen content and temperature. By considering a change of a mean distance between neighboring nitrogen atoms, we concluded that the microscopic structure of E N is not only an isolated nitrogen atom but also nitrogen-related complex, accompanied by low-order pairs of nitrogen atoms and/or nitrogen clusters.
-
The effects of indium pre-evaporation on rotational twin formation in GaAs films on Si(111)
Suzuki H., Ito D., Haga A., Fukuyama A., Ikari T.
2014 IEEE 40th Photovoltaic Specialist Conference, PVSC 2014 1830 - 1833 2014年10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：2014 IEEE 40th Photovoltaic Specialist Conference, PVSC 2014
© 2014 IEEE. The effects of In pre-evaporation on the formation of rotational twin domains (TW) in GaAs layers on Si (111) substrates were systematically investigated. Atomic arrangements of In atoms on the Si substrate during pre-evaporation were studied and resulting formation of TW were discussed. The pre-evaporation of In resulted in the formation of InAs islands. The size of InAs islands was smaller than that of GaAs islands grown on Si substrate without In pre-evaporation. The amount of TW increased with increasing sizes of GaAs or InAs at initial phase. These results suggested that the size of island formed during the initial pre-evaporation phase could control the TW growth in the final GaAs film.
-
Aihara T., Fukuyama A., Yokoyama Y., Kojima M., Suzuki H., Sugiyama M., Nakano Y., Ikari T.
Journal of Applied Physics 116 ( 4 ) 2014年7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
To investigate the effect of the miniband formation on the optical absorption spectrum, we adopted two non-destructive methodologies of piezoelectric photothermal (PPT) and photoreflectance (PR) spectroscopies for strain-balanced InGaAs/GaAsP multiple quantum-well (MQW) and superlattice (SL) structures inserted GaAs p-i-n solar cells. Because the barrier widths of the SL sample were very thin, miniband formations caused by coupling the wave functions between adjacent wells were expected. From PR measurements, a critical energy corresponding to the inter-subband transition between first-order electron and hole subbands was estimated for MQW sample, whereas two critical energies corresponding to the mini-Brillouin-zone center (Ω) and edge (p) were obtained for SL sample. The miniband width was calculated to be 19 meV on the basis of the energy difference between Ω and p. This coincided with the value of 16 meV calculated using the simple Kronig-Penney potential models. The obtained PPT spectrum for the SL sample was decomposed into the excitonic absorption and inter-miniband transition components. The latter component was expressed using the arcsine-like signal rise corresponding to the Ω point in the mini-Brillouin zone that was enhanced by the Sommerfeld factor. The usefulness of the PPT methodology for investigating the inserted MQW and/or SL structure inserted solar cells is clearly demonstrated. © 2014 AIP Publishing LLC.
DOI： 10.1063/1.4887443
-
Suzuki A., Fukuyama A., Suzuki H., Sakai K., Paek J., Yamaguchi M., Ikari T.
Japanese Journal of Applied Physics 53 ( 5 SPEC. ISSUE 1 ) 2014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：Japanese Journal of Applied Physics
The effect of Be doping on the crystal structure and the optical properties of catalyst-free Be-doped GaAs nanowires (NWs) grown on a (111)Si substrate were investigated by scanning transmission electron microscopy (STEM), X-ray diffraction (XRD) analysis, and photoreflectance (PR) and photoluminescence (PL) techniques. Be-doped NWs sample showed a striped pattern in STEM images. Owing to a high arsenic flux under the growth condition, the sample did not have a wurtzite but a zinc-blend (ZB) structure, and the observed striped pattern in STEM images suggests the presence of twin boundaries and stacking faults. The bandgap energy of the Be-doped NWs was lower than that of the nondoped NWs sample in the entire temperature range. In addition, the deviation from the conventional Varshni curve was found to be large in the low-temperature region. However, this is well explained by considering the strong electron-phonon interaction and high average phonon temperature. Therefore, we concluded that the induced strain increased the linear thermal expansion coefficient. This is because the Be atom has a smaller covalent radius than the Ga and As atoms. © 2014 The Japan Society of Applied Physics.
-
N-H related defects in GaAsN grown through chemical beam epitaxy
Ohshita Y., Ikeda K., Suzuki H., Machida H., Sudoh H., Tanaka T., Honda T., Inagaki M., Yamaguchi M.
Japanese Journal of Applied Physics 53 ( 3 ) 2014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：Japanese Journal of Applied Physics
The local vibration modes of N-H related defects in GaAsN are studied using isotopes. When GaAsN is grown through chemical beam epitaxy (CBE) using triethylgallium/tris(dimethylamino)arsenic/monomethylhydrazine gas, there are several local vibration modes (LVMs) in Fourier transform infrared (FTIR) spectra. Signals with stretching mode peaks at 2952, 3098, and 3125 cm -1 are reported, along with new wagging and stretching mode peaks at 960 and 3011 cm -1 , which exist only in crystals grown through CBE. When the film is grown using deuterated MMHy as a nitrogen source, new peaks at 2206, 2302, 2318, 2245, and 714cm -1 appear. This suggests that D related defects are created because of the deuterated MMHy. The ratios of frequencies of these new peaks to those obtained from crystals grown using MMHy are nearly 1.34. This suggests that all defects in GaAsN grown through CBE, which appear as LVMs, are N-H related defects. Especially, those with LVMs at 960 and 3011 cm -1 are new N-H defects only found in GaAsN grown through CBE. © 2014 The Japan Society of Applied Physics.
-
Optical properties of Be-doped GaAs nanowires on Si substrate grown by a catalyst-free molecular beam epitaxy vapor–liquid–solid method 査読あり
Akio Suzuki, Atsuhiko Fukuyama, Hidetoshi Suzuki, Kentaro Sakai, Ji-Hyun Paek, Masahito Yamaguchi, Tetsuo Ikari
Japanese Journal of Applied Physics 53 05FV03 2014年2月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
Fukuyama A., Aihara T., Yokoyama Y., Kojima M., Fujii H., Suzuki H., Sugiyama M., Nakano Y., Ikari T.
Physica Status Solidi (A) Applications and Materials Science 211 ( 2 ) 444 - 448 2014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：Physica Status Solidi (A) Applications and Materials Science
Effect of an internal built-in electric field on the non-radiative recombination process of strain-balanced InGaAs/GaAsP multiple quantum wells (MQWs) inserted into a GaAs p-i-n solar cell structure was investigated using the piezoelectric photo-thermal technique. From the experimental data obtained from two types of p-i-n solar cell structures with partly charge-neutral and uniform-gradient potentials, the decrease in the built-in electric field contributed to the decrease in the non-radiative carrier recombination in the MQW. This phenomenon was especially pronounced in the higher photon energy of the incident light and in large quantum well stack number. With the increase in the photon energy, the penetration length shortened, and most carriers were generated in the charge-neutral area in the i-region. The present experimental results could be understood by the increase in the radiative recombination processes within the MQW because of the wave function overlap is essentially unity. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
-
Effects of nitrogen precursor on the Au-assisted vapor–liquid–solid growth of GaAs(N) nanostructures 査読あり
Hidetoshi Suzuki, Kentaro Sakai, Tomohiro Haraguchi, Toshihiro Yamauchi, Masanobu Hijii, Kouji Maeda, Tetsuo
Journal of Crystal Growth 386 100 - 106 2014年1月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
Ding W., Fukuyama A., Morioka G., Suzuki A., Suzuki H., Yamaguchi M., Ikari T.
Energy Procedia 60 ( C ) 63 - 70 2014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：Energy Procedia
© 2014 The Authors. To investigate the microstructure of nitrogen-induced localized state (EN) that perturbs the conduction band of GaAs host material, we adopted the photoreflectance measurements to chemical-beam-epitaxy and flow-rate modulated chemical-beamepitaxy grown GaAsN thin films. We measured both two split subbands to estimate correct values of EN. It was clearly seen that estimated EN decreased with increasing nitrogen content and temperature. By considering a change of a mean distance between adjacent nitrogen atoms, we concluded that the microscopic structure of EN is not only an isolated nitrogen atom but also nitrogen-related complex, accompanied by low-order pairs of nitrogen atoms and/or nitrogen clusters.
-
Nitrogen-induced localized level observed by photoreflectance in GaAsN thin films grown by chemical beam epitaxy 査読あり
Hidetoshi Suzuki, Akio Suzuki, Atsuhiko Fukuyama, Tetsuo Ikari
Journal of Crystal Growth 384 5 - 8 2013年12月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
Phtotovoltaic systems in university of Miyazaki
Yoshino K., Nishioka K., Fukuyama A., Suzuki H., Otsubo M.
Applied Mechanics and Materials 372 555 - 558 2013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：Applied Mechanics and Materials
We organized a project of solar cells in University of Miyazaki in order to develop the technologies for solar cells. We have four kinds PV module systems, such as hybrid Si Thin film (1 kW), Poly-Si (50 kW), CIS (100 kW) and CPV (14 kW×2). Their total is 179 kW. These take appoximately 5% of total electricity of the university. © (2013) Trans Tech Publications, Switzerland.
-
Misfit dislocation anisotropies in the InGaAs/GaAs(001) interface measured using X-ray topography and reciprocal space mapping 査読あり
Hidetoshi Suzuki, Takuya Matsushita, Masahiro Katayama, Kouji Maeda, Tetsuo Ikari
Japanese Journal of Applied Physics 53 018001 2013年10月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
Reduction of rotational twin formation by indium pre-evaporation in epitaxially grown GaAs films on Si (111) substrate 査読あり
Hidetoshi Suzuki, Daiki Ito, Atsuhiko Fukuyama, Tetsuo Ikari
Jornal of Crystal Growth 380 148 - 152 2013年10月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
原料供給シーケンスの違いが原子層エピタキシー法によるGaAsN薄膜成長に与える影響
芳賀 章博, 貞任 萌, 原口 智宏, 鈴木 秀俊, 福山 敦彦, 尾関 雅志, 碇 哲雄
宮崎大學工學部紀要 42 27 - 30 2013年8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）
-
Si(111)表面へのIII族供給によるGaAs薄膜中の回転双晶軽減
伊東 大樹, 太刀掛 弘晃, 鈴木 秀俊, 福山 敦彦, 碇 哲雄
宮崎大學工學部紀要 42 19 - 22 2013年8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）
-
逆格子マッピングによる成長初期のInGaAs/GaAs(001)界面のミスフィット転位の解析
松下 卓哉, 高比良 潤, 境 健太郎, 前田 幸治, 鈴木 秀俊
宮崎大學工學部紀要 42 85 - 88 2013年8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）
-
III-V-N materials for super-high efficiency multi junction solar cells 査読あり
Ikeda K., Yamaguchi M., Bouzazi B., Suzuki H., Kojima N., Ohshita Y.
Japanese Journal of Applied Physics 52 ( 8 PART 2 ) 08JH11 - 08JH11-4 2013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
The majority and minority carrier traps in GaAsN grown by chemical beam epitaxy (CBE) and their relationships with the electrical properties of the materials and solar cells are presented. By adopting a new flow-rate modulation CBE (FM-CBE) method, a higher mobility and a longer minoritycarrier lifetime than those obtained by other growth methods have been achieved. We have characterized deep levels in grown GaAsN films by deep-level transient spectroscopy (DLTS). As a result, we found that 1) a hole trap H2 center (Ev + 0:15 eV) in p-GaAsN acts as an acceptor state and correlates with N concentration, 2) an electron trap E2 (Ec 0:33 eV) center in n-GaAsN and p-GaAsN is a non-radiative recombination center and 3) a hole trap H1 center (Ev + 0.052 eV) newly observed in p-GaAsN acts as an acceptor state and a radiative recombination center. Although further analyses are required, it is very important to reduce the E1 defect density in (In)GaAsN to understand the degradation mechanism of the CBE-grown (In)GaAsN solar cell property and realize a higher efficiency. © 2013 The Japan Society of Applied Physics.
-
Effects of gas-flow sequences on the self-limiting mechanisms of GaAsN films grown by atomic layer epitaxy 査読あり
Hidetoshi Suzuki, Hajime Sadato, Tomohiro Haraguchi, Toshihiro Yamauchi, Masashi Ozeki, Tetsuo Ikari
Thin Solid Films 540 79 - 83 2013年7月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
Honda Takahiko, Ikeda Kazuma, Inagaki Makoto, Suzuki Hidetoshi, Kojima Nobuaki, Ohshita Yoshio, Yamaguchi Masafumi
Jpn J Appl Phys 52 ( 5 ) 59201 - 059201-1 2013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：The Japan Society of Applied Physics
-
Acceptor Levels due to a Complex Including the Nitrogen–Hydrogen Bond in GaAsN Films Grown by Chemical Beam Epitaxy 査読あり
Hidetoshi Suzuki, Atsuhiko Fukuyama, Tetsuo Ikari
Japanese Journal of Applied Physics 52 052001-1 - 052001-5 2013年3月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
In situ three-dimensional X-ray reciprocal-space mapping of GaAs epitaxial films on Si(001) 査読あり
Takahasi M., Nakata Y., Suzuki H., Ikeda K., Kozu M., Hu W., Ohshita Y.
Journal of Crystal Growth 378 34 - 36 2013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：Journal of Crystal Growth
The molecular-beam epitaxial growth processes of GaAs on Si(001) were investigated using in situ synchrotron X-ray diffraction. Three-dimensional X-ray intensity distributions around the Si and GaAs 022 Bragg points in reciprocal space were measured during growth using combination of an area detector and one-axis scans. During the initial stage of growth, the average radius of GaAs islands was found to follow a second power law function of the growth time, in accordance with the growth being limited by the binding of Ga with As at step edges. With increasing GaAs thickness, streaky scattering extending from the GaAs 022 peak in the < 111 > directions was observed, indicating the development of plane defects. © 2013 Elsevier B.V. All rights reserved.
-
Real-time observation of crystallographic tilting ingaas layers on GaAs offcut substrates 査読あり
Nishi T., Sasaki T., Ikeda K., Suzuki H., Takahasi M., Shimomura K., Kojima N., Ohshita Y., Yamaguchi M.
AIP Conference Proceedings 1556 14 - 17 2013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：AIP Conference Proceedings
© 2013 AIP Publishing. In situ X-ray reciprocal space mapping during In x Ga 1-x As/GaAs(001) MBE growth is performed to investigate effects of substrate misorientations on crystallographic tilting. It was found that evolution of the crystallographic tilt for the InGaAs films is strongly dependent on both layer structures and substrate misorientations. We discuss these observations in terms of an asymmetric distribution of dislocations.
DOI： 10.1063/1.4822188
-
Suzuki H., Sasaki T., Takahasi M., Ohshita Y., Yamaguchi M.
Materials Science Forum 725 89 - 92 2012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：Materials Science Forum
The effects of In incorporation on anisotropies in the strain relaxation mechanisms of InGaAs on GaAs systems are investigated using a three-dimensional reciprocal space mapping (3D-RSM) technique. Relaxation processes are classified as belonging to one of the following four phases: no relaxation, gradual relaxation, rapid relaxation, and relaxation saturation. Anisotropies appear in the gradual relaxation phase and almost disappear in the rapid relaxation phase. These anisotropies are enhanced by In content. When In content is low, both α- and β-misfit dislocations (MDs) are observed at the same thickness; the density of α-MDs increases more rapidly than that of β-MDs. When In content is high, only β-MDs appear in the gradual relaxation phase. These results suggest that In atoms prevent nucleation and/or gliding of β-MDs. © (2012) Trans Tech Publications, Switzerland.
-
Kashima K., Fukuyama A., Nakano Y., Inagaki M., Suzuki H., Yamaguchi M., Ikari T.
Materials Science Forum 725 93 - 96 2012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：Materials Science Forum
The temperature dependences of the piezoelectric photo-thermal (PPT) signals from unintentionally doped p-type GaAsN films grown on semi-insulating GaAs substrate were measured in the temperature range from 80 to 300 K. From the theoretical analysis based on the rate equation for the recombination of photo excited carriers to the localized levels, we identified five hole traps. Among them, estimated concentrations of the two traps increased with increasing the nitrogen contents. Therefore, we concluded that these two traps were due to nitrogen-related levels in GaAsN. © (2012) Trans Tech Publications, Switzerland.
-
III-V-N materials for super high-efficiency multijunction solar cells
Yamaguchi M., Bouzazi B., Suzuki H., Ikeda K., Kojima N., Ohshita Y.
AIP Conference Proceedings 1477 24 - 27 2012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：AIP Conference Proceedings
We have been studying concentrator multi-junction solar cells under Japanese Innovative Photovoltaic R & D program since FY2008. 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. This paper presents our major results in the understanding of majority and minority carrier traps in GaAsN grown by chemical beam epitaxy and their relationships with the poor electrical properties of the materials. © 2012 American Institute of Physics.
DOI： 10.1063/1.4753825
-
Suzuki H., Sasaki T., Yamamoto S., Ohshita Y., Fukuyama A., Yamaguchi M.
Materials Science Forum 725 85 - 88 2012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 Science Forum
Anisotropies in misfit dislocations (MDs) at the InGaAs/GaAs(001) interface are investigated by monochromatic X-ray topography (XRT). In the XRT image, white lines with different width are observed. These lines are related to a single MD line or several MD lines (MD bunching). The distribution, density, and number of MDs in one MD bunch are evaluated. The density of α-MDs is higher than that of β-MDs. The MDs in one MD bunch distribute with two peaks in both in-plane directions. In a macroscopic view, the a-MD bunching lay more orderly than the α-MD bunching, whereas in a microscopic view, β-MDs gather in a range narrower than p-MDs. © (2012) Trans Tech Publications, Switzerland.
-
(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.
-
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.
-
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）
-
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）
-
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.
-
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.
-
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
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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
-
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.
-
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.
-
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.
-
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.
-
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
-
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.
-
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
-
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.
-
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.
-
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.
-
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.
-
Suzuki H., Nishimura K., Saito K., Ohshita Y., Kojima N., Yamaguchi M.
Journal of Crystal Growth 311 ( 10 ) 2821 - 2824 2009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：Journal of Crystal Growth
The change in the surface concentration of N ([N] s ) on a GaAs surface under N and As source injections is investigated using the N atomic layer doping (N-ALD) technique, and the key factor determining [N] s is discussed. The As and N precursors source gases are trisdimethylaminoarsenic (TDMAAs, [N (CH 3 ) 2 ] 3 As) and monomethylhydrazine (MMHy, N 2 H 3 CH 3 ), respectively. N-ALD layers are prepared by using two gas injection sequences (A: MMHy injection and B: MMHy and TDMAAs injections). [N] s increases with decreasing growth temperature in both sequences. [N] s in sequence A is higher than that of sequence B. In sequence B, Δ [N] s / Δ t is proportional to exp (- t / τ N ), where t and τ N are the gas injection time and the residence time of N, respectively. It is observed that the number of vacant sites, [V] s, N , remaining constant during gas injections. In sequence A, Δ [N] s / Δ t cannot be fitted by a single exponential function, indicating that [V] s, N is not constant. From these results, we suggest that the vacant sites at the surface are created not only by N desorption but also by As desorption. It has been found that As desorption is enhanced by MMHy injection. As desorption reaction has been confirmed by in situ auger electron spectroscopy measurements. These results indicate that [N] s is determined by the competitive absorption between N and As, [V] s, N , and τ N . © 2009 Elsevier B.V. All rights reserved.
-
Fabrication of GaAsN homo-junction solar cells by chemical beam epitaxy
Suzuki H., Nishimura K., Hashiguchi T., Saito K., Balasubramanian B., Yamamoto S., Inagaki M., Ohshita Y., Kojima N., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2008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 reduction of residual acceptors in GaAsN films and the improvement of GaAsN crystal quality evidenced by hole mobility and PL intensity were reported. Si doping using a SiH 4 gas was also studied. Based on these results GaAsN homo-junction solar cells were fabricated by CBE at the first time. The short circuit current, open circuit voltage, fill factor and conversion efficiency of the GaAsN solar cell are 8.99 mA/cm 2 , 0.48 V, 0.43, and 1.93 %, respectively. © 2008 IEEE.
-
Electrical properties of Mg doped C60 thin films
Kojima N., Natori M., Suzuki H., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2008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
C 60 solids have been known as high resistive semiconductor materials. Such high resistivity is one of the reasons of low charge transport efficiency in organic solar cells. Mg doping in C 60 films was done by the co-evaporation method of C 60 and Mg sources. The conductivity could be controlled by the composition ratio of Mg/C 60 , and its dependence is divided into 3 ranges (Mg/C 60 = 0∼2, 2∼6, ≫6). Temperature dependence of the conductivity shows hopping conduction mechanism, and suggesting the same hopping center origin in the first and second ranges. From Raman scattering spectroscopy and XRD measurements, the crystal structure disordering by Mg-doping was observed. It is thought that Mg composition dependence of the conductivity is related to both of the conduction mechanism change and the structural change. © 2008 IEEE.
-
Crystal structures of copper-phthalocyanine on C60(111) surface grown by molecular beam epitaxy
Suzuki H., Yamashita Y., Kojima N., Yamaguchi M.
Japanese Journal of Applied Physics 47 ( 8 PART 3 ) 6879 - 6882 2008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：Japanese Journal of Applied Physics
Crystal orientation and morphologies of copper-phthalocyanine (CuPc) on the C 60 (111) surface were investigated. CuPc thin films were grown on C 60 (111) by the molecular beam epitaxy technique. The CuPc molecular column was parallel to the C 60 (111) surface. CuPc formed two types of structure on C 60 (111). Structure 1 was shaped similarly to straight fibers and covered the entire surface. Structure 1 lay along three directions equivalent to 〈112〉 on C 60 (111). This indicated the epitaxial growth of CuPc on the C 60 (111) surfaces. Structure 2 was also fiberlike in shape and dispersed randomly on Structure 1. Both structures were observed on the CaPc/C 60 (111) surface at growth temperatures of 60-160 °C. The orientation of Ce 60 (111) surfaces affected the formation of CuPc crystals even at 60 °C. ©2008 The Japan Society of Applied Physics.
DOI： 10.1143/JJAP.47.6879
-
Suzuki H., Nishimura K., Saito K., Hashiguchi T., Ohshita Y., Kojima N., Yamaguchi M.
Japanese Journal of Applied Physics 47 ( 8 PART 3 ) 6910 - 6913 2008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：Japanese Journal of Applied Physics
The electrical behavior of nitrogen-hydrogen (N-H) complexes and carbon (C) atoms in GaAsN films grown by the chemical beam epitaxy (CBE) method have been studied by comparing H concentrations and hole concentrations. The contributions of H and C concentrations ([H] and [C] ) to ionized impurity scattering have been also investigated. In the GaAsN films, there were three acceptor levels (A0, A1, and A2). The energy levels of A1 and A2 were 130 and 55meV, respectively. The concentration of the deepest acceptor (A0) was more than 10 19 cm -3 , which was higher than [H] and [C] . A2 was observed only in films with a high [C]. The amount of A1 was proportional to [H] . Most of the residual H formed N-H complexes; thus, it is concluded that the N-H complex behaved as an acceptor in GaAsN films. At low temperatures, ionized impurity scattering limited the total hole mobility. The inverse numbers of the coefficients for the ionized scattering were consistent with [C] instead of [H] . This suggests that all the residual C atoms were ionized owing to compensation by the donors. A disagreement between N composition and alloy scattering has been also detected. This might indicate a fluctuation in the N composition in the GaAsN films. © 2008 The Japan Society of Applied Physics.
DOI： 10.1143/JJAP.47.6910
-
Carbon reduction in GaAsN thin films by flow-rate-modulated chemical beam epitaxy
Nishimura K., Suzuki H., Saito K., Ohshita Y., Kojima N., Yamaguchi M.
Japanese Journal of Applied Physics 47 ( 4 PART 1 ) 2072 - 2075 2008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
The flow-rate-modulated chemical beam epitaxy (FM-CBE) method was developed and implemented on the basis of the discussion of the desorption velocities of absorbed species originating from N source gas [MMHy, (CH 3 )N 2 H 3 ] for decreasing the residual carbon (C) concentration in GaAsN films. In this method, the Ga source [TEGa, Ga(C 2 H 5 ) 3 ] was supplied intermittently, while the As [TDMAAs, As(N(CH 3 ) 2 ) 3 ] and N sources (MMHy) were supplied continuously. Below growth temperatures of 440°C, the residual C concentrations in GaAsN films was reduced to 1/10 that in conventional CBE films, with no change in N concentration. However, above 440°C, N concentration decreased drastically with FM-CBE. It was concluded that the reduction in C concentration by FM-CBE was attributed to the decrease in -NHCH 3 coverage on the growing surface by -NH 2 substitution during the intermittence of the TEGa flow. FM-CBE was an effective method for decreasing residual C concentration while maintaining the N concentration in GaAsN films below 440°C. © 2008 The Japan Society of Applied Physics.
DOI： 10.1143/JJAP.47.2072
-
Hydrogen reduction in GaAsN thin films by flow rate modulated chemical beam epitaxy
Saito K., Nishimura K., Suzuki H., Ohshita Y., Yamaguchi M.
Thin Solid Films 516 ( 11 ) 3517 - 3520 2008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：Thin Solid Films
The amount of residual H in the GaAsN film grown by chemical beam epitaxy (CBE) can be decreased by flow rate modulation growth. Many H atoms in the films grown by CBE exist as N-H or N-H 2 structures. Although a higher growth temperature was required for decreasing the H concentration ([H]), it caused a decrease in the N concentration ([N] ). A reduction in [H] while keeping [N] constant was necessary. By providing an intermittent supply of Ga source while continuously supplying As and N sources, [H] effectively decreased in comparison with the [H] value in the film grown at the same temperature by conventional CBE without reducing [N]. © 2007 Elsevier B.V. All rights reserved.
-
Al-induced one dimensional nano-facet formation on Si(113) surface
Mino M., Nakahara H., Saito Y., Suzuki H.
e-Journal of Surface Science and Nanotechnology 6 45 - 48 2008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：e-Journal of Surface Science and Nanotechnology
We have studied surface morphology and surface reconstruction of an Al adsorbed Si(113) surface using a scanning tunneling microscope. A clean Si(113) surface is atomically flat, but well-ordered one-dimensional (1D) nano-facet structures with their width of about 2.5 nm are formed on this surface after 1 ML of Al deposition. In the faceting process, the initial stage is Al atoms replacement with Si atoms at 0.4 ML of Al deposition. Replaced Si atoms stick to steps, causing the change of steps shape. These Si atoms also form two-dimensional (2D) islands. The next stage is growth of 2D islands toward [3̄3̄2] direction at 0.6 ML of Al deposition. At this coverage, 2D islands consist of (9̄61), (69̄1), and (332̄) steps. For further Al deposition, (9̄61) and (69̄1) steps become unstable and (332̄) and (3̄3̄2) steps become stable. Finally, (332̄) and (3̄3̄2) steps change into two kinds of nano-facet structures, i.e. (112) and (115) facets. Pn the (112) facet, a mixture of N X 1 structures (N = 3-8) is observed. The most abundant value of N is 6, which well agrees with the first principle calculation. While on the (115) facet, 4 × 1 structures areobserved. © 2008 The Surface Science Society of Japan.
-
Novel materials for high-efficiency III-V multi-junction solar cells
Yamaguchi M., Nishimura K., Sasaki T., Suzuki H., Arafune K., Kojima N., Ohsita Y., Okada Y., Yamamoto A., Takamoto T., Araki K.
Solar Energy 82 ( 2 ) 173 - 180 2008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：Solar Energy
As a result of developing wide bandgap InGaP double hetero structure tunnel junction for sub-cell interconnection, InGaAs middle cell lattice-matched to Ge substrate, and InGaP-Ge heteroface structure bottom cell, we have demonstrated 38.9% efficiency at 489-suns AM1.5 with InGaP/InGaP/Ge 3-junction solar cells by in-house measurements. In addition, as a result of developing a non-imaging Fresnel lens as primary optics, a glass-rod kaleidoscope homogenizer as secondary optics and heat conductive concentrator solar cell modules, we have demonstrated 28.9% efficiency with 550-suns concentrator cell modules with an area of 5445 cm 2 . In order to realize 40% and 50% efficiency, new approaches for novel materials and structures are being studied. We have obtained the following results: (1) improvements of lattice-mismatched InGaP/InGaAs/Ge 3-junction solar cell property as a result of dislocation density reduction by using thermal cycle annealing, (2) high quality (In)GaAsN material for 4- and 5-junction applications by chemical beam epitaxy, (3) 11.27% efficiency InGaAsN single-junction cells, (4) 18.27% efficiency InGaAs/GaAs potentially modulated quantum well cells, and (5) 7.65% efficiency InAs quantum dot cells. © 2007 Elsevier Ltd. All rights reserved.
-
Electrical properties of GaAsN film grown by chemical beam epitaxy
Nishimura K., Suzuki H., Saito K., Ohshita Y., Kojima N., Yamaguchi M.
Physica B: Condensed Matter 401-402 343 - 346 2007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：Physica B: Condensed Matter
The local vibrational modes (LVMs) observed by Fourier transform infrared (FTIR) spectroscopy in GaAsN films grown by chemical beam epitaxy (CBE) was studied, and the influence of the nitrogen-hydrogen bond (N-H) concentration on the hole concentration was investigated. The absorption peak around 936 cm -1 is suggested to be the second harmonic mode of the substitutional N, N As , LVM around 469 cm -1 . The absorption peak around 960 cm -1 is suggested to be the wagging mode of the N-H, where the stretch mode is observed around 3098 cm -1 . The hole concentration linearly increases with increasing N-H concentration, and the slope increases with increasing growth temperature. It indicates that the hole concentration in GaAsN film is determined by both the number of the N-H and unknown defect, such as impurities, vacancies, and interstitials. This defect concentration increases with increasing growth temperature, suggesting that it is determined by Arrhenius type reaction. © 2007 Elsevier B.V. All rights reserved.
-
Role of nitrogen and impurity on free carrier concentration in GaAsN grown by chemical beam epitaxy
Imai T., Lee H., Nishimura K., Suzuki H., Kawahigashi T., Sasaki T., Ohshita Y., Yamaguchi M.
Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4 1 842 - 844 2007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 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4
GaAsN thin films were grown by chemical beam epitaxy using monomethylhydrazine ((CH 3 )N 2 H 3 ) as the N sources, and the role of the nitrogen (N) and impurities (hydrogen (H), carbon (C)) on free carrier concentration was investigated. The N, H, and C concentrations increased with decreasing growth temperature. GaAsN thin film grown at 470°C was n-type conduction, and the donor is thought to be the same in GaAs thin film. On the other hand, the films grown at 390-460°C were p-type conduction. In the range of 420-460°C, the hole concentration increased with decreasing growth temperature, and it decreased below 420°C, respectively. In order to clarify the origin of acceptor in p-GaAsN thin films, the dependence of growth temperature on the hole concentration and N, H, and C concentration were investigated, and the relationship between them was discussed. © 2006 IEEE.
-
Reduction of residual carbon in GaAsN films grown by chemical beam epitaxy
Suzuki H., Nishimura K., Lee H., Saito K., Kawahigashi T., Imai T., Ohshita Y., Yamaguchi M.
Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4 1 819 - 822 2007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 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4
Crystal quality of GaAsN films can be improved by using chemical beam epitaxy method for low-temperature growth. However, low-temperature growth increases carbon (C) incorporation in the films, which degrades their electrical properties. To reduce the C concentration in the films, C incorporation process was investigated in view of the surface reaction of nitrogen (N) sources on a substrate surface, and monomethylhydrazine (MMHy) and 1,1-dimethylhydrazine (DMHy) were compared. When MMHy was used as an N source, the C concentration in GaAsN drastically increases below 380°C than that in GaAs due to insufficient CH x desorption. In the case of DMHy, N(CH 3 ) 2 is desorbed more readily than CH x , Therefore, the C concentration can then be reduced by using DMHy. © 2006 IEEE.
-
Novel materials and structures for super high efficiency multi-junction solar cells
Yamaguchi M., Suzuki H., Nishimura K., Kojima N., Ohsita Y., Okada Y.
ISES Solar World Congress 2007, ISES 2007 2 1028 - 1032 2007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：ISES Solar World Congress 2007, ISES 2007
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. As a result of developing wide bandgap InGaP double hetero structure tunnel junction for sub-cell interconnection, InGaAs middle cell lattice-matched to Ge substrate, and InGaP-Ge heteroface structure bottom cell, we have demonstrated 38.9% efficiency at 489-suns AM1.5 with InGaP/InGaP/Ge 3-junction solar cells In order to realize 40% and 50% efficiency, new approaches for novel materials and structures are being studied. We have obtained promising results: 1) high quality (In)GaAsN material with higher mobility by chemical beam epitaxy compared to those grown by the other growth methods, 2) 11.27% efficiency InGaAsN single-junction cells for 4-and 5-junction applications.
-
Mg doping in C<inf>60</inf> layer for C<inf>60</inf>/a-C superlattice solar cells
Kojima N., Terayama T., Honda K., Suzuki H., Ohshita Y., Yamaguchi M.
Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4 1 53 - 55 2007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 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4
Carbon materials can be expected as one of the promising materials for next generation low-cost solar cells. We have proposed C 60 /a-C superlattice structures as absorption layers. Superlattice structure has advantages to control the optical and electrical properties easily. In this paper, we will report Mg-doping in C 60 films to control the conductivity of C 60 layers for C 60 /a-C superlattice solar cells. Mg doping in C 60 films was done by the co-evaporation method of C 60 and Mg sources. The resistivity of Mg-doped C 60 films reduces in 6 orders of magnitude at the ratio of Mg/C 60 of 0.57. It is thought that Mg atoms act as dopant effectively. © 2006 IEEE.
-
Interface structure analysis between C60 and CuPc for organic solar cells
Yamashita Y., Suzuki H., Kojima N., Ohshita Y., Yamaguchi M.
Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4 1 263 - 266 2007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 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4
The CuPc crystal structure and molecular orientation on the C 60 was investigated by AFM and XRD as preliminary step to clarify the relationship the interface structure and electric property for organic solar cells. It is figure out that the CuPc grows grainy on the C 60 by the AFM measurement. The area density of the CuPc grain on the C 60 /mica became larger, and the grain diameter became smaller with increasing the substrate temperature. By the XRD, it became clear that the CuPc forms a-type mainly. The molecular column of deposited CuPc on C60 would be parallel to the substrate surface. © 2006 IEEE.
-
Nishimura K., Lee H., Suzuki H., Kawahigashi T., Imai T., Saito K., Ohshita Y., Yamaguchi M.
Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4 1 815 - 818 2007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 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4
GaAsN epitaxial thin films were grown on GaAs (001) substrate by chemical beam epitaxy with dimethylhydrazine ((CH 3 ) 2 N 2 H 2 ). In the dependence of growth temperature on the N concentration, there were three distinct regions in which the dependence was different. At the growth temperature of 420°C, the N concentration increased with increasing surface step density that corresponds to misorientation angle of GaAs (001) substrate. When the samples grown on 2 and 10° off substrates were compared, the root-mean-squares of surface roughness decreased from 1.1 nm to 0.3nm, despite of the increase of N concentration. In addition, the reduction of the impurity concentrations (hydrogen and carbon) in the sample grown on the 10° off substrate was also observed. These results showed the surface morphology of the GaAsN thin films is affected by the step density, and the possibility to obtain (In)GaAsN thin film that has high N and low impurity concentration with keeping crystal quality. © 2006 IEEE.
-
Hydrogen treatment effects of a-C films for C<inf>60</inf>/a-C superlattice solar cells
Honda K., Kojima N., Imaizumi T., Terayama T., Suzuki H., Ohshita Y., Yamaguchi M.
Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4 1 142 - 145 2007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 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4
The film quality improvement of amorphous carbon (a-C) layers for C 60 /a-C superlattice solar cells has been intended. a-C:N films were deposited by C 60 -cage breaking, and the layer-by-layer hydrogen treatment method was applied to the a-C:N films for the improvement of the film quality, and the structural change by the hydrogen treatment was investigated. Hydrogen radicals reconstruct carbon bonding structure of a-C:N film surface by etching the weak carbon bonds. Such structural change causes reducing the optical gap and changing the peak intensity ratio of Raman scattering spectra, which is concerned with sp 2 cluster size. The spin defect density much depends on the hydrogen treatment time. It is clear that the spin defect density has minimum at the particular time of the hydrogen treatment, so that hydrogen radicals also affect to cut the carbon bonds and induce defects. It is necessary to optimize hydrogen treatment time to improve film quality. ©2006 IEEE.
-
Chemical beam epitaxy of GaAsN thin films with monomethylhydrazine as N source
Nishimura K., Lee H., Suzuki H., Ohshita Y., Yamaguchi M.
Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers 46 ( 5 A ) 2844 - 2847 2007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, Part 1: Regular Papers and Short Notes and Review Papers
GaAsN thin films were grown by chemical beam epitaxy (CBE) with monomethylhydrazine (MMHy) as a N source. Processes that determine the N composition in the GaAsN thin films were investigated in the growth temperature range from 340 to 480°C. When growth temperature is low (340-390°C), N composition is mainly determined by the supply of N species generated from MMHy and growth rate, since the desorption rate of N species from the growing surface is low. The effect of the desorption of N species on N composition is enhanced by increasing growth temperature (390-445°C). When growth temperature is high (445-480°C), the degree of N atom segregation from the grown layer increases, resulting in a marked decrease in N composition. Thus, N composition is determined by the balance of supply and desorption of N species, and growth rate. © 2007 The Japan Society of Applied Physics.
DOI： 10.1143/JJAP.46.2844
-
Suzuki H., Nishimura K., Lee H., Ohshita Y., Kojima N., Yamaguchi M.
Thin Solid Films 515 ( 12 ) 5008 - 5011 2007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：Thin Solid Films
Crystal quality of GaAsN films can be improved by using CBE for low-temperature growth. However, low-temperature growth increases C incorporation in the films, which degrades their electrical properties. Consequently, C incorporation was investigated in view of the surface reaction of N sources on a substrate surface, and MMHy and DMHy were compared. When MMHy was used as an N source, C concentration in GaAsN drastically increases below 380 °C than that in GaAs due to insufficient CH x desorption. In the case of DMHy, N(CH 3 ) 2 is desorbed more readily than CH x , therefore, the C concentration can then be reduced using DMHy. © 2006 Elsevier B.V. All rights reserved.
-
Influence of surface steps on N incorporation in GaAsN grown by chemical beam epitaxy
Nishimura K., Lee H., Suzuki H., Kawahigashi T., Imai T., Saito K., Ohshita Y., Yamaguchi M.
Physica Status Solidi (C) Current Topics in Solid State Physics 3 ( 8 ) 2689 - 2692 2006年10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
GaAsN epitaxial thin films were grown on GaAs (001) substrate by chemical beam epitaxy (CBE) with dimethylhydrazine ((CH 3 ) 2 N 2 H 2 , DMHy) as the N source that decomposes at a low temperature. We investigated the influences of the gas flow ratio of DMHy to the group V sources ([DMHy]/V), and surface steps on the N composition in GaAsN thin films. At the growth temperature of 420 °C, the N composition increased with increasing [DMHy] /V, indicating the N composition is determined by the amount of N supplied to the growing surface. In addition, the N composition also increased with increasing surface step density on GaAs (001) substrate orientated towards [010] from 0 to 10°. However, when the density of surface step is low (0-3 × 10 2 μm -1 ), the dependence of N composition on surface step density cannot be explained by only the N incorporation at the surface steps on the GaAs substrate. In this case, the surface morphology thought to be rough, since it suggest that N atoms are incorporated at the steps around the nuclei on the growing surface. On the contrary, when the density of surface step is high (3-7 × 10 2 μm -1 ), the N incorporation occurs at the steps as they move forward, resulting in the flat surface morphology. It was confirmed by the surface morphology observation of the samples grown on 2 and 10° off substrates, and the root-mean-squares of surface roughness were 1.1 and 0.3nm, respectively. These results indicate the surface morphology of the GaAsN thin films is affected strongly by the step density. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.
-
Nitrogen incorporation in GaAsN grown by chemical beam epitaxy
Ohshita Y., Nishimura K., Lee H., Kojima N., Gono I., Suzuki H., Yamaguchi M.
Proceedings - Electrochemical Society PV 2005-04 272 - 277 2005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 - Electrochemical Society
Chemical beam epitaxial growth system has been developed for achieving good quality InGaAsN thin film, which will be adopted as a third material of four-junction tandem solar cell. Methylhydrazine, which was used as a N source, was decomposed on the growing surface. Between 400-420°C, N concentration had slight temperature dependence. The adsorbed N-related molecules hindered the decomposition of Ga precursor TEG on the surface, resulting in the decrease of the growth. Above 440°C, the number of N incorporated in the grown film swiftly decreased. The growth rate had slight temperature dependence and the quality of grown film became deteriorated although the amount of residual N decreased.
-
C60/a-C superlattice structures for solar cell applications
Kojima N., Terayama T., Suzuki H., Imaizumi T., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 118 - 120 2005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
C 60 / amorphous carbon (a-C) superlattice structures were fabricated by shutter controlled molecular beam deposition. A-C layers were transformed from C 60 by nitrogen ion bombardment. The dark and photo conductivity of C 60 /a-C superlattice structures were measured by gap-cell structure. The resulted films show high resistivity, and the photosensitivity ratio is ranged 9-16. It is thought that such low photosensitivity is caused by high defect density of 2.7×10 21 cm -3 in the a-C layers. Use of hydrogen plasma in C 60 amorphization process, instead of nitrogen, reduces the spin defect density in two orders of magnitude. Hydrogen atoms effectively reduce the defect density of a-C films by etching the weak carbon bond structures and/or passivating the dangling bonds. © 2005 IEEE.
-
Nishimura K., Lee H., Suzuki H., Gono I., Kojima N., Ohshita Y., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 722 - 724 2005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
GaInNAs films for the ultra high-efficiency ( > 40%) 4-junction tandem space solar cells ((Al)GaInP/GaAs/ GaInNAs/Ge) have been grown by using chemical beam epitaxy (CBE) in this study. In the growth of GaInNAs films, the selection of nitrogen source and understanding of nitrogen incorporation is important because nitrogen is play an important role in the crystallization and electrical properties of III-V-N compound materials. A proper nitrogen source between monomethylhydrazine (MMHy) and dimethylhydrazine (DMHy) was investigated, and the nitrogen incorporation in samples grown with MMHy was higher. From the dependence of nitrogen concentration on the substrate temperature, three distinct regions were observed, even in the nitrogen concentration usually decreased with increasing the substrate temperature, and a low FWHM value was obtained at an intermediate temperature. In addition, the dependence of the nitrogen incorporation on the ratio of N/(N+As) was investigated, and at a low temperature, the nitrogen concentration increased with increasing the ratio of N/(N+As). From these results, the nitrogen incorporation in GaInNAs films grown with the substrate temperature and the ratio of N/V elements in CBE technique is clarified, and the relationships between the nitrogen incorporation and crystallization of GaInNAs are clear. ©2005 IEEE.
-
Structure of the Si(1 1 3) surface studied by surface X-ray diffraction
Mizuno Y., Akimoto K., Aoyama T., Suzuki H., Nakahara H., Ichimiya A., Sumitani K., Takahashi T., Zhang X., Sugiyama H., Kawata H.
Applied Surface Science 237 ( 1-4 ) 40 - 44 2004年10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 Surface Science
We carried out a grazing incidence X-ray diffraction analysis of the Si(113) 3 × 1 surface using synchrotron radiation. We compared the experimental structure factors obtained from the integrated intensities of the fractional-order reflections with the calculated structure factors of the dimerized structure model of Ranke. By minimizing the R-factor, we determined the position and the size of the pentagon in the 3 × 1 dimerized structure model of Ranke. In addition, we found that a model with randomly distributed interstitial atoms at the center of the pentagon gi ves a smaller R-factor value. © 2004 Elsevier B.V. All rights reserved.
-
Ga-induced nano-facet formation on Si(1 1 n) surfaces
Nakahara H., Suzuki H., Miyata S., Ichimiya A.
Applied Surface Science 212-213 ( SPEC. ) 334 - 338 2003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 Surface Science
Surface morphology of three kinds of Si(1 1 n) surfaces during Ga deposition has been studied by scanning tunneling microscopy to investigate nano-facet formation processes on high-index silicon surfaces. It has been observed that Si(1 1 3) surfaces with vicinal angles of ±2° changed into nano-facet structures of (1 1 2) and (1 1 5) at 1 ML Ga deposition as well as a flat Si(1 1 3). In contrast, no faceting occurred on Si(1 1 4). In all cases of nano-facet formation, (1 1 2) facet formed prior to (1 1 5) facet. Thus, it is considered that (1 1 2) facet formation is a driving force of nano-facet formation process. It is also considered that large angle difference between (1 1 2) and (1 1 4) prevents the facet formation on Si(1 1 4). Difference of vicinal direction appears in distribution of facet width. The facet width distribution strongly depends on the initial morphology on the surface tilted toward [3 3 2̄] direction, while on the surface tilted toward [3 ̄ 3̄ 2] , initial morphology does not affect the final facet distribution. © 2003 Elsevier Science B.V. All rights reserved.
-
Surface morphology of Ga adsorbed Si(1 1 3) surface
Suzuki H., Nakahara H., Miyata S., Ichimiya A.
Surface Science 493 ( 1-3 ) 166 - 172 2001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：Surface Science
Surface morphology and reconstruction of Ga adsorbed Si(1 1 3) surface have been investigated using scanning tunneling microscopy and reflection high-energy electron diffraction. Surface reconstruction changes from clean 3 × 2 structure to 3 × 1 structure at 0.2 ML Ga deposition. Then the surface changes to 2 × 2 structure at 0.4 ML Ga deposition. For more than 1 ML Ga deposition, well-ordered one-dimensional facet structure is formed with its width of about 5 nm. The two faces of the facet are determined as (1 1 2) and (1 1 5) surfaces. The surfaces have N × 1 (N=4-8) and 4 × 1 reconstructions, respectively. On (1 1 2) facet, mostly observed structure is 6 × 1, and this result agrees with previously reported result of Ga deposition on flat (1 1 2) surface. While on (1 1 5) surface, two kinds of 4 × 1 structures which are symmetric to [332̄] direction are observed. It is considered that nucleation of (1 1 2) facet leads a flat (1 1 3) surface to facet structure. © 2001 Elsevier Science B.V. All rights reserved.