Papers - Araki Kenji
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Research and Development on Concentrator Photovoltaic in the World Reviewed
ARAKI Kenji, YAMAGUCHI Masahumi
Journal of Japan Solar Energy Society 29 ( 5 ) 31 - 39 2003.9
Language：English Publishing type：Research paper (scientific journal)
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Solar Collector and Module for Cocentration Photo-voltaic Systems Reviewed
AKISAWA Atsushi, EGAMI Toshio, ARAKI Kenji
Journal of Japan Solar Energy Society 29 ( 5 ) 13 - 19 2003.9
Language：English Publishing type：Research paper (scientific journal)
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Extended distributed model for analysis of non-ideal concentration operation Reviewed
Araki K., Yamaguchi M.
Solar Energy Materials and Solar Cells 75 ( 3-4 ) 467 - 473 2003.2
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy Materials and Solar Cells
Non-ideal illumination is often observed in practical concentrator systems. The simulation to that problem was usually done by a time-consuming 2D numerical calculation or a linear approximation of algebraic calculation. This paper proposes a simple method to anticipate non-linear response to non-ideal illumination operation for concentrator cells. © 2002 Elsevier Science B.V. All rights reserved.
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Sunshine environment and spectrum analysis for concentrator PV systems in Japan Reviewed
Araki K., Yamaguchi M.
Solar Energy Materials and Solar Cells 75 ( 3-4 ) 715 - 721 2003.2
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy Materials and Solar Cells
Normal direct irradiance levels for concentrator photovoltaic were investigated and anticipated in 26 sunshine regions in Japan. The spectrum and photon numbers were also examined. Normal direct photon number was assumed to be 92-60% of global the sunshine on sloped surfaces in all the districts in Japan. © 2002 Elsevier Science B.V. All rights reserved.
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Strategies for improving radiation tolerance of Si space solar cells Reviewed
Khan A., Yamaguchi M., Ohshita Y., Dharmaraso N., Araki K., Khanh V., Itoh H., Ohshima T., Imaizumi M., Matsuda S.
Solar Energy Materials and Solar Cells 75 ( 1-2 ) 271 - 276 2003.1
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy Materials and Solar Cells
The present study explored first time the better radiation tolerance of gallium-doped silicon solar cells as compared to conventional boron-doped silicon solar cells after heavy fluence of 1MeV electron irradiation. One of the approaches to improve the end of life of silicon solar cells is by increasing the effective base carrier concentrations. Analysis of the carrier removal rate RC in boron, gallium and aluminum-doped Si solar cells showed that carrier removal effects can be partially offset by using gallium as dopant instead of boron. © 2002 Elsevier Science B.V. All rights reserved.
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Development of a metal homogenizer for concentrator monolithic multi-junction-cells Reviewed
Araki K., Leutz R., Kondo M., Akisawa A., Kashiwagi T., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 1572 - 1575 2002.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
A high reflectance, low cost and robust metal homogenizer suitable for monolithic multi-junction concentrator cells was developed. Mismatching loss caused by chromatic aberration and FF loss caused by flux intensity inhomogenity are shown to have significantly improved.
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Japanese R&D activities of multi-junction and concentrator solar cells Reviewed
Yamaguchi M., Araki K.
Conference Record of the IEEE Photovoltaic Specialists Conference 820 - 823 2002.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
Japanese R&D activities of concentrator solar cells and systems are overviewed. Japan Energy developed high efficiency (31.7% at 1-sun AM1.5G) InGaP/InGaAs/Ge 3-junction cell under support by NEDO (New En-ergy and Industrial Technology Development Organization) in addition to the world-record efficiency InGaP/GaAs//InGaAs 3-junction cell (33.3% at 1-sun AM1.5G) by Japan Energy, Sumitomo and TTI. This project is now taken over by Sharp and targeted to concentration application also supported by NEDO. The new target is 40% efficiency under 500-sun concentration by March 2006. The SPFG (Single and non-alignment Photolithography Fine Grid) silicon cell is developed by TTI. The first prototype of non-imaging Fresnel lens, which expands acceptance half angle to 2°/12° and enabled low cost 1-axis tracker was fabricated and tested by TUAT. The module with this nonimaging lens and the SPFG cell is now assembled and subjected to be tested.
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Vu T., Ohshita Y., Araki K., Yamaguchi M.
Journal of Applied Physics 91 ( 8 ) 4853 - 4856 2002.4
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics
Defects that reduce the minority-carrier lifetime in silicon crystal are produced by minority-carrier injection (forward bias or light illumination) when the boron-doped Czochralski-grown silicon (Cz-Si) is used as a solar cell material. The number of induced defects is determined from changes in open-circuit voltage (V OC) of the cells. It increases with the carrier injection time, and then becomes saturated. The saturated value increases as the ambient temperature increases, during the carrier injection. These defects are observed to be vanished by thermal annealing at 200°C for 20 min, indicating that they are in an unstable state and that some of them are annihilated even during the carrier injection. Therefore, the total number of induced defects to be determined by the difference between the generation and the annihilation rates. The activation energies for the generation process and annihilation process are evaluated to be 0.77 eV and 0.32 eV, respectively. © 2002 American Institute of Physics.
DOI： 10.1063/1.1459609
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26pWE-3 Optical spin injection into Si substrate across the GaAs/GaAsP/Si interfaces Reviewed
Torikai E., Wakahara K., Ikedo Y., Shimomura K., Nagamine K., Saka T., Kato T., Araki K., Mizuno Y.
Meeting Abstracts of the Physical Society of Japan 57 ( 0 ) 2002
Language：English Publishing type：Research paper (scientific journal) Publisher：The Physical Society of Japan
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Khan A., Yamaguchi M., Ohshita Y., Dharmarasu N., Araki K., Abe T., Itoh H., Ohshima T., Imaizumi M., Matsuda S.
Journal of Applied Physics 90 ( 3 ) 1170 - 1178 2001.8
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics
The present extensive systematic study of defect introduction rates as a function of boron, gallium, oxygen, and carbon concentrations by means of deep level transient spectroscopy has drawn a quite complete picture towards the identification of the dominant radiation-induced defects in Si. The radiation-induced defect EV+ 0.36 eV has been identified as Ci-Oi complexes. The absence of an EC - 0.18 eV complex center in gallium-doped samples and the linear dependence of its introduction rates on both the boron and oxygen content fixed its identification as the Bi- Oi complex in boron-doped Si. One of the technologically important results of present study is that the gallium appears to strongly suppress the radiation induced defects, especially hole level EV+0.36eV (Ci-Oi), which is thought to act as a recombination center as well as the dominant compensating center at EC-0.18eV (Bi-Oi). As a result, the effects of lifetime degradation and carrier removal could be partially offset to higher radiation fluences by using Ga as a dopant instead of boron in Si space solar cells. The anneal out of the new hole level EV+0.18eV in gallium-doped samples at around 350°C, together with recovery of free carrier concentration, suggests that this level may act as a donor-like center which compensates free carrier concentration in gallium-doped Si. © 2001 American Institute of Physics.
DOI： 10.1063/1.1384855
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Characteristics of GaAs-based concentrator cells Reviewed
Araki K., Yamaguchi M., Takamoto T., Ikeda E., Agui T., Kurita H., Takahashi K., Unno T.
Solar Energy Materials and Solar Cells 66 ( 1-4 ) 559 - 565 2001.2
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy Materials and Solar Cells
GaAs-based cells, including GaAs single-junction cells, AlGaAs/GaAs two-junction cells, and InGaP/GaAs two-junction cells grown on GaAs substrates by metal-organic chemical vapor deposition (MOCVD) are examined in various levels of concentration and backside cooling temperature. All types of cells have shown boost of efficiency in low and medium ranges of concentration. The cell efficiencies obtained are 31.5% at 20-suns of AM1.5 for InGaP/GaAs tandem cell, and 29.2% at 7-suns of AM1.5 for AlGaAs/GaAs tandem cell, respectively. The GaAs single-junction cell is also examined as the reference. A new equivalent circuit model reveals that increase of apparent leakage current is responsible for a rapid efficiency drop in the high-concentration region. It is possible to improve it by reducing contact resistance and using uniform concentrated illumination.
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Impact of boron and gallium on defects production in silicon Reviewed
Khan A., Dharmarasu N., Yamaguchi M., Araki K., Vu T., Saga T., Abe T., Annzawa O., Imaizumi M., Matsuda S.
Materials Research Society Symposium-Proceedings 650 2001
Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Research Society Symposium-Proceedings
We report the results of comparison of radiation-induced defects (1 MeV electrons) in n+-p-p+ Si diodes doped with gallium or boron ranging in concentration from 8 × 1014 to 5 × 1016 cm-3, together with the impact of oxygen on radiation-induced defects. Present results provide evidence for new defects states in addition to those previously reported in gallium- and boron-doped Si. The combined boron and gallium data provide enough information to gain valuable insight into the role of the dopants on radiation-induced defects in Si. The interesting new future of our results is that the gallium appears to strongly suppress the radiation induced defect, especially hole level EV+0.36 eV, which is thought to act as a recombination center. Similarly the dominant electron level at EC-0.18 eV in B-doped Si (which act as a donor) has not been observed in Ga-doped CZ-grown Si. © 2001 Materials Research Society.
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Magnetic Materials and Semiconductors. A Concentrator Si Solar Cell Made by Low-cost Process. Reviewed
Araki Kenji, Yamaguchi Masafumi
DENKI-SEIKO 71 ( 4 ) 303 - 309 2000
Language：English Publishing type：Research paper (scientific journal) Publisher：Daido Steel Co., Ltd.
Obviously, concentrator solar cells reduce the total area of cells required, which provides lower system costs. For non-concentrator solar panels, the solar cells represent 80% of the system cost. The use of concentrator cells provides a cost reduction for cells inversely proportional to the concentration ratio. However conventional Si concentrator cells normally require more complex photolithography which increases the cost of manufacture. In this novel approach a single step photolithography process is described which includes superfine random pyramid texture, with the electrode directly defined onto the textured surface. Additionally, improved electrode design was applied, allowing for operation under non-uniform surface voltage and current density, experienced during high concentrator conditions. This has lead to energy conversion efficiencies in excess of 19%. Experimental results on the conversion efficiency are in good agreement with the results calculated by the proposed equations taking into account of the distributed diode effect at high concentration ratio.
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AM0 concentration operation of III-V compounds solar cells
Araki K., Yamaguchi M., Imaizumi M., Matsuda S., Takamoto T., Kurita H.
Conference Record of the IEEE Photovoltaic Specialists Conference 2000-January 968 - 971 2000
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2000 IEEE. III-V compounds solar cells were examined by concentration illumination of AM0 sunlight. High concentration or non-uniform illumination was found to bring significance degradation of FF due to apparent degradation of a diode ideality factor or "rounded" I-V curve. The output current at the maximum power point dropped as a result. This paper covers an experimental evaluation, analysis and solutions to that problem. The quantified approach was highly generalized and could be applied every type of high efficiency solar cells. It was found that a distributed diode model [1] explained a behavior of the I-V curve under high concentration or non-uniform concentration operation. The output current drop was responsible from modulation of surface voltage of the emitter. Raised voltage at inter-grid region ignited parasitic diodes and had it leak a part of the output current. For the purpose of quantified analysis and solutions, the distributed diode model [1] was expanded. Behaviors of l-V curve or FF were described by simple arithmetic functions with two basic new parameters, a non-dimensional finger pitch and a normalized resistance, which were independent to the type of solar cells, accompanied with the combination of cell-dependent basic parameters, such as Voc or Isc. The impact to FF degradation could be summarized into counter plots. Basic design parameters such as finger pitch and series resistance could be designed with avoiding FF degradation by high concentration illumination. It did not require complicated numerical calculations. It was found that reduction of series resistance was not very important for multi-junction space concentrator cells. The key was reduction of non-dimensional finger pitch and maintenance of uniform surface voltage. For single junction concentrator cells such as a silicon cell, still, series resistance was essential.
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Silicon concentrator cells by low cost process Reviewed
Araki K., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2000-January 164 - 167 2000
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2000 IEEE. A new Si concentrator cell was proposed and developed. In this novel approach a single step photolithography process is described which includes superfine random pyramid texture, with the electrode directly defined onto the textured surface. Additionally, improved electrode design was applied, allowing for operation under non-uniform surface voltage and current density, experienced during high concentrator conditions. This has lead to energy conversion efficiencies in excess of 19%.
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Planar, contact, yoke GMR head vs. conventional, flying, shielded GMR head: A comparative study Reviewed
Yoshida Y., Araki K., Sugano S., Kaneta Y.
IEEE Transactions on Magnetics 34 ( 4 PART 1 ) 1507 - 1509 1998.12
Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Magnetics
A comparative study was conducted between planar, contact, yoke GMR (Giant Magneto-resistive) heads and conventional, flying, shielded GMR heads by modeling. Magnetic flux efficiencies to the GMR element of the various planar yoke GMR heads were estimated using the reluctance network method and FEM (Finite Element Method). Results showed that it would be necessary to separate the reading magnetic circuit from the writing magnetic circuit in order to obtain higher efficiencies which could be up to 37%. S and 10 Gbits/in2 recording simulation shows that the shielded GMR are expected to be superior to the yoke GMR even at 10 Gbite/in2 but yoke GMR will start to show its advantages in the higher capability of writing and ease of processing at higher densities. © 1998 IEEE.
DOI： 10.1109/20.706598
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Shiosaki T., Adachi M., Kobayashi H., Araki K., Kawabata A.
Japanese Journal of Applied Physics 24 25 - 27 1985.1
Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics
Transparent, core-free and good quality single crystals of Li2B4O7 have been successfully grown by the Czochralski method. All dielectric, elastic and piezoelectric constants, and their first- and second-order temperature coefficients have been determined by measuring resonant and antiresonant frequencies of bars and plates with various orientations. The theoretical and experimental results show the potential usefulness of Li2B4O7 for bulk wave or SAW applications. Further, measurements on optical, acousto-optic and electro-optic properties of Li2B4O7 have also been carried out. © 1985 IOP Publishing Ltd.