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Journal Articles

Radiation degradation and damage coefficients of InGaP/GaAs/Ge triple-junction solar cell by low-energy electrons

Imaizumi, Mitsuru*; Morioka, Chiharu*; Sumita, Taishi*; Oshima, Takeshi; Okuda, Shuichi*

Proceedings of 37th IEEE Photovoltaic Specialists Conference (PVSC-37) (CD-ROM), p.1579 - 1582, 2011/06

InGaP single-junction and InGaP/GaAs/Ge triple-junction (3J) solar cells were irradiated with low energy electrons. The energy of electrons were selected around the threshold energy of Gallium and Indium recoiling in the InGaP system (300 keV). Simultaneous electron irradiation and current-voltage characteristics measurement of the cells revealed the fact that the short-circuit current (Isc) of InGaP cells and consequently the 3J cells does not degrade when the cells are irradiated with electrons with energies of less than 300 keV, while the open-circuit voltage (Voc) considerably degrades for both types of the cell, regardless of the electron energies. This result suggests that the effects of defects generated by the recoil of phosphorus are insufficient to decrease the minority-carrier lifetime in InGaP. In addition, the degradation of the Voc suggests an increase in surface recombination.

Journal Articles

Analysis for radiation-resistance of InGaP and GaAs sub-cells for InGaP/GaAs/Ge 3-junction solar cells

Yamaguchi, Masafumi*; Ekins-Daukes, N. J.*; Lee, H. S.*; Sumita, Taishi*; Imaizumi, Mitsuru*; Takamoto, Tatsuya*; Agui, Takaaki*; Kaneiwa, Minoru*; Kamimura, Kunio*; Oshima, Takeshi; et al.

Proceedings of 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion (WCPEC-4) (CD-ROM), p.1789 - 1792, 2006/05

no abstracts in English

Journal Articles

Evaluation of the electrical characteristics of III-V compounds solar cells irradiated with protons at low temperature

Oshima, Takeshi; Sumita, Taishi*; Imaizumi, Mitsuru*; Kawakita, Shiro*; Shimazaki, Kazunori*; Kuwajima, Saburo*; Oi, Akihiko*; Ito, Hisayoshi

Proceedings of 31st IEEE Photovoltaic Specialists Conference and Exhibition (PVSC-31), p.806 - 809, 2005/00

no abstracts in English

Journal Articles

Analysis of EOL prediction methodology for triple-junction solar cells in actual radiation environment

Sumita, Taishi*; Imaizumi, Mitsuru*; Oshima, Takeshi; Ito, Hisayoshi; Kuwajima, Saburo*

Proceedings of 31st IEEE Photovoltaic Specialists Conference and Exhibition (PVSC-31), p.667 - 670, 2005/00

no abstracts in English

Journal Articles

Analysis of flight demonstration results of an InGaP/GaAs dual-junction tandem solar cell

Imaizumi, Mitsuru*; Sumita, Taishi*; Kawakita, Shiro*; Oshima, Takeshi; Ito, Hisayoshi; Kuwajima, Saburo*

Proceedings of 31st IEEE Photovoltaic Specialists Conference and Exhibition (PVSC-31), p.563 - 566, 2005/00

no abstracts in English

Journal Articles

Study of radiation response on single-junction component sub-cells in triple-junction solar cells

Imaizumi, Mitsuru*; Takamoto, Tatsuya*; Sumita, Taishi*; Oshima, Takeshi; Yamaguchi, Masafumi*; Matsuda, Sumio*; Oi, Akihiko; Kamiya, Tomihiro

Proceedings of 3rd World Conference on Photovoltaic Energy Conversion (WCPEC-3) (CD-ROM), 4 Pages, 2004/01

The radiation response of InGaP, InGaAs and Ge single junction sub-cells in the triple junction space solar cell are studied in order to develop a device simulator which predicts the End-Of-Life performance of space solar cells. InGaP top-cells show no significant difference in radiation response between under AM0 light and dark conditions during irradiation. The radiation resistance of InGaAs cell which is used as middle cell decreases with increasing In contents. The Ge cell shows lower radiation reisitance as compared to InGaP and InGaAs cells.

Journal Articles

Super radiation tolerance of CIGS solar cells demonstrated in space by MDS-1 satellite

Kawakita, Shiro*; Imaizumi, Mitsuru*; Sumita, Taishi*; Kushiya, Katsumi*; Oshima, Takeshi; Yamaguchi, Masafumi*; Matsuda, Sumio*; Yoda, Shinichi*; Kamiya, Tomihiro

Proceedings of 3rd World Conference on Photovoltaic Energy Conversion (WCPEC-3) (CD-ROM), 4 Pages, 2004/01

The electrical performance of Cu(Ga,In)Se$$_{2}$$ solar cells on MDS-1 which was launched in February 2002 was measured. The CIGS solar cells show superior radiation resistance in space. The short circuit current dose not degrade and the open circuit voltage shows only 1 % degradation after 200 days. On the other hand, in the case of ground test, the recovery of electrical performance of CIGS solar cells are observed at RT. And, the recovery is enhanced by current-injection.

Journal Articles

Analysis of end-of-life performance for proton-irradiated triple-junction space solar cell

Sumita, Taishi*; Imaizumi, Mitsuru*; Matsuda, Sumio*; Oshima, Takeshi; Oi, Akihiko; Kamiya, Tomihiro

Proceedings of 3rd World Conference on Photovoltaic Energy Conversion (WCPEC-3) (CD-ROM), 4 Pages, 2004/01

While high beginning-of-life efficiencies are important for space solar cells, the end-of-life performance is also critical factor. Two different prediction methods, "relative damage dose" and "displacement damage dose" methods, based on analysis of ground radiation test have been produced. We report proton radiation response for triple-junction space solar cells and analyze prediction methodology for the cell radiation response using the two methods. The results show that V$$_{OC}$$ degradation behavior can be predicted by taking into account a cell structure and proton penetration depth. Accurate prediction of power degradation, however, is required to determine the current-limiting sub cell after proton irradiations.

Journal Articles

Sulfur-doping of rutile-titanium dioxide by ion implantation; Photocurrent spectroscopy and first-principles band calculation studies

Umebayashi, Tsutomu; Yamaki, Tetsuya; Yamamoto, Shunya; Miyashita, Atsumi; Tanaka, Shigeru; Sumita, Taishi*; Asai, Keisuke*

Journal of Applied Physics, 93(9), p.5156 - 5160, 2003/05

 Times Cited Count:288 Percentile:98.71(Physics, Applied)

Sulfur (S)-doped titanium dioxide (TiO$$_{2}$$) was synthesized by ion implantation and subsequent thermal annealing. Compared to the pure TiO$$_{2}$$, a photocurrent was observed in the lower energy regions for the S-doped TiO$$_{2}$$. Based on the theoretical analyses by the first principles band calculations using the full potential linearized augmented plane wave methods within the generalized gradient approximation, the mixing of the S 3p states with the valence band (VB) was found to contribute to the increasing width of the VB. This leads to the bandgap narrowing in the S-doped TiO$$_{2}$$. Therefore, the photon-to-carrier conversion was induced during irradiation by visible light above 420 nm ($$<$$ 2.9 eV).

Journal Articles

UV-ray photoelectron and ab initio band calculation studies on electronic structures of Cr- or Nb-ion implanted titanium dioxide

Umebayashi, Tsutomu; Yamaki, Tetsuya; Sumita, Taishi*; Yamamoto, Shunya; Tanaka, Shigeru; Asai, Keisuke*

Nuclear Instruments and Methods in Physics Research B, 206, p.264 - 267, 2003/05

 Times Cited Count:24 Percentile:83.46(Instruments & Instrumentation)

Chromium (Cr) and niobium (Nb) were implanted into single-crystalline titanium dioxide (TiO$$_{2}$$; rutile). After annealing at 600$$^{circ}$$C for the Cr-implanted sample or at 1000$$^{circ}$$C for the Nb-implanted sample, the radiation damage was recovered. The implanted metals occupied titanium (Ti) sites in TiO$$_{2}$$ to form metal-oxygen bonds. According to the ultraviolet-ray photoelectron spectra, a localized level due to the implanted metals was formed in band gap of both the crystals. This position was close to the VB edge for the Cr-doped TiO$$_{2}$$, while the Nb-doped TiO$$_{2}$$ had the small peak far from the edge. This is in good agreement with the ab-initio band calculation results. It is considered that the midgap states of Cr- and Nb-doped TiO$$_{2}$$ consist of the Cr t$$_{2g }$$ or Ti t$$_{2g }$$ state, respectively.

Journal Articles

Proton radiation analysis of multi-junction space solar cells

Sumita, Taishi*; Imaizumi, Mitsuru*; Matsuda, Sumio*; Oshima, Takeshi; Oi, Akihiko; Ito, Hisayoshi

Nuclear Instruments and Methods in Physics Research B, 206, p.448 - 451, 2003/05

 Times Cited Count:44 Percentile:93.04(Instruments & Instrumentation)

Proton irradiation effects of triple-junction (InGaP/GaAs/Ge) solar cells for space use were studied. The changes in electrical and optical properties of the solar cells irradiated with protons at energies between 20 keV and 10 MeV were examined. As the result of analyzing the relationship between proton projection range and the degradation of their properties, the largest degradation of the properties was observed when proton projection range is near the junction of GaAs sub-cells. This indicates that improvement of the radiation resistance of GaAs is necessary to enhance radiation resistance of tliple-junction solar cells.

Journal Articles

Influence of carbon-ion irradiation and hydrogen-plasma treatment on photocatalytic properties of titanium dioxide films

Choi, Y.; Yamamoto, Shunya; Saito, Hiroshi*; Sumita, Taishi*; Ito, Hisayoshi

Nuclear Instruments and Methods in Physics Research B, 206(1-4), p.241 - 244, 2003/05

 Times Cited Count:7 Percentile:47.94(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Fluorine-doping in titanium dioxide by ion implantation technique

Yamaki, Tetsuya; Umebayashi, Tsutomu; Sumita, Taishi*; Yamamoto, Shunya; Maekawa, Masaki; Kawasuso, Atsuo; Ito, Hisayoshi

Nuclear Instruments and Methods in Physics Research B, 206(1-4), p.254 - 258, 2003/05

 Times Cited Count:134 Percentile:99.07(Instruments & Instrumentation)

Single crystalline titanium dioxide (TiO$$_{2}$$) rutile were implanted with 200keV F$$^{+}$$ at a nominal fluence of 1$$times$$10$$^{16}$$ to 1$$times$$10$$^{17}$$ ions cm$$^{-2}$$ and then thermally annealed in air up to 1200$$^{circ}C$$ for 5h. The radiation damage and its recovery during the subsequent annealing were analyzed by Rutherford backscattering spectrometry in channeling geometry and variable-energy positron annihilation spectroscopy. The lattice disorder was completely annealed at 1200$$^{circ}C$$ by the diffusion of point defects to the surface acting as a sink. According to the secondary ion mass spectrometry, the F depth profile was shifted to a shallower region along with the damage recovery, finally producing an F-doped layer where the impurity concentration increased steadily towards the surface. The F doping proved to provide a small modification to the conduction-band edge of TiO$$_{2}$$, as assessed by theoretical band calculations.

Journal Articles

Photo-induced surface charge separation in Cr-implanted TiO$$_2$$ thin film

Sumita, Taishi*; Yamaki, Tetsuya; Yamamoto, Shunya; Miyashita, Atsumi

Thin Solid Films, 416(1-2), p.80 - 84, 2002/09

 Times Cited Count:22 Percentile:70.84(Materials Science, Multidisciplinary)

Surface charge separation efficiencies of uniformly Cr-distributed rutile grown by pulse laser deposition(PLD) using Cr/TiO$$_2$$ multi-targets and rutile with Cr concentration gradient produced by ion implantation with the appropriate post-annealing process were characterized by photo-induced transient charge separation (PITCS) measurement. Cr depth profiles were obtained by secondary ion mass spectrometry(SIMS) and X-ray photoelectron spectroscopy(XPS) was used to determine that both surface Cr concentrations were the same. PITCS can be measured without direct contacts and without an externally applied field, and demonstrate the inherent property of charge separation without disturbing spontaneously formed surface band bending. There was a large charge separation for implanted rutile with Cr gradient, even in the visible light region ($$sim$$520nm), which was more remarkable than that of uniform rutile and epitaxial anatase films.

Journal Articles

Preparation of anatase and rutile thin films by controlling oxygen partial pressure

Syarif, D. G.; Miyashita, Atsumi; Yamaki, Tetsuya; Sumita, Taishi*; Choi, Y.; Ito, Hisayoshi

Applied Surface Science, 193(1-4), p.287 - 292, 2002/06

 Times Cited Count:87 Percentile:93.75(Chemistry, Physical)

Titanium dioxide ($$rm TiO_2$$) films on glass substrates were prepared by pulsed laser deposition (PLD) technique. The dependence of crystal structure, morphology and photocatalytic activity on oxygen partial pressure were investigated using X-ray diffraction (XRD), Atomic force microscope (AFM) and UV-VIS Spectrophotometer. By increasing oxygen partial pressure, the surface morphology changed from smooth to rough, and the crystal structure changed from rutile to anatase at fixed substrate temperature of 773 K. The change of the surface morphology and the formation of anatase structure by variation of oxygen partial pressure resulted in an increase of photocatalytic activity.

Journal Articles

Characterization of epitaxial TiO$$_{2}$$ films prepared by pulsed laser deposition

Yamamoto, Shunya; Sumita, Taishi; Yamaki, Tetsuya; Miyashita, Atsumi; Naramoto, Hiroshi

Journal of Crystal Growth, 237-239(Part1), p.569 - 573, 2002/04

The epitaxial growth of TiO$$_{2}$$ films has attracted much interest from the viewpoints of basic science and applications. In the present study, it is shown that TiO$$_{2}$$ films with anatase or rutile structure can be grown by pulsed laser deposition(PLD) with an ArF excimer laser under the controlled O$$_{2}$$ atmosphere. The TiO$$_{2}$$ films were prepared on the LaAlO$$_{3}$$, LSAT SrTiO$$_{3}$$ and $$alpha$$-Al$$_{2}$$O$$_{3}$$ single crystal substrates. The epitaxial films were analyzed by RBS and X-ray diffraction for investigating the crystallographic relationships with the substrates. The high quality anatase TiO$$_{2}$$(001) films have been successfully grown on the LaAlO$$_{3}$$ (001), LSAT (001) and SrTiO$$_{3}$$ (001) substrates at temperatures above 500$$^{circ}$$C. Also the high quality rutile TiO$$_{2}$$(100) and (001) films were obtained on the $$alpha$$-Al$$_{2}$$O$$_{3}$$ (0001) and (10-10), respectively.The optical properties were characterized by optical absorption measurements. The optical band gaps for anatase and rutile TiO$$_{2}$$ epitaxial films were evaluated to be 3.22 eV and 3.11 eV, respectively.

Journal Articles

Preparation of epitaxial TiO$$_{2}$$ films by PLD for photocatalyst applications

Yamaki, Tetsuya; Sumita, Taishi; Yamamoto, Shunya; Miyashita, Atsumi

Journal of Crystal Growth, 237-239(Part1), p.574 - 579, 2002/04

Pulsed laser deposition (PLD) with a KrF excimer laser was used to prepare epitaxial TiO$$_{2}$$ films on a (0001) sapphire substrate. The crystalline structure and surface morphology of the films were then investigated as a function of the laser power density in the PLD. X-ray diffraction and Raman spectroscopy results showed that the films were composed of the (100) oriented rutile phase with a small amount of the (001) oriented anatase. The anatase-to-rutile ratio in such phase-mixed films was controlled by the laser power; the ratio increased as the power density decreased. From atomic force microscopy observations, the film deposited at the lowest power was found to have a rough surface consisting of coarse grains. This film exhibited the best photocatalytic performance during the decomposition of the organic dyes possibly due to the maximum relative content of anatase and the large surface area.

Journal Articles

Preparation of epitaxial TiO$$_{2}$$ films by pulsed laser deposition technique

Yamamoto, Shunya; Sumita, Taishi; Sugiharuto; Miyashita, Atsumi; Naramoto, Hiroshi

Thin Solid Films, 401(1-2), p.88 - 93, 2001/12

 Times Cited Count:124 Percentile:96.95(Materials Science, Multidisciplinary)

The epitaxial growth of high-quality TiO$$_{2}$$ films has attracted much interest from the viewpoints of basic science and applications. In this study, it is shown that TiO$$_{2}$$ films with anatase and rutile structure can be prepared by pulsed laser deposition (PLD) with a Nd-YAG laser under the controlled O$$_{2}$$ atmosphere. The TiO$$_{2}$$ films with 200 nm thickness were prepared on the SrTiO$$_{3}$$, LaAlO$$_{3}$$, LSAT and $$alpha$$-Al$$_{2}$$O$$_{3}$$ single crystal substrates. The epitaxial films were analyzed by Rutherford backscattering spectrometry (RBS) combined with channeling and X-ray diffraction for the crystallographic relationships with the substrates. The high quality anatase TiO$$_{2}$$ (001) films have been successfully prepared on the LaAlO$$_{3}$$ (001), LSAT (001) and SrTiO$$_{3}$$ (001) substrates about 500$$^{circ}$$C substrate temperature. Also the high quality rutile TiO$$_{2}$$ (100) and TiO$$_{2}$$ (001) films were obtained on the $$alpha$$-Al$$_{2}$$O$$_{3}$$ (0001) and (10$$bar{1}$$0), respectively.

Journal Articles

A New characterization method of photocatalytic activity in semiconductor photocatalysts

Sumita, Taishi; Yamaki, Tetsuya; Yamamoto, Shunya; Miyashita, Atsumi

Japanese Journal of Applied Physics, Part 1, 40(6A), p.4007 - 4008, 2001/06

 Times Cited Count:7 Percentile:35.19(Physics, Applied)

We propose a new simple method for characterizing photocatalytic activity by measuring photo-generated transient charge separation at the surface of semiconductor photocatalysts. In this method, the charge separation generated by a pulse dye laser is obtained as a function of the incident laser energy. Using this method, the photocatalytic activity and the type of surface reaction (reduction or oxidation) in titanium dioxide films were rapidly determined.

Journal Articles

Preparation of TiO$$_{2}$$-anatase film on Si(001) substrate with TiN and SrTiO$$_{3}$$ as buffer layers

Sugiharuto; Yamamoto, Shunya; Sumita, Taishi; Miyashita, Atsumi

Journal of Physics; Condensed Matter, 13(13), p.2875 - 2881, 2001/04

 Times Cited Count:14 Percentile:61.06(Physics, Condensed Matter)

An epitaxial TiO$$_{2}$$-anatase thin film was grown on the Si(001) substrate with SrTiO$$_{3}$$/TiN as the buffer layers by pulsed laser deposition technique under an oxygen gas supply. The characterization of the epitaxial TiO$$_{2}$$-anatase film was performed using the X-ray diffraction method. The crystallographic relationships between the TiO$$_{2}$$-anatase film and SrTiO$$_{3}$$/TiN buffer layers were analyzed by the $$theta$$-2$$theta$$ scan and pole figure measurement. The growth direction of the films was determined as $$rm TiO_{2}langle 001rangle$$ / $$rm SrTiO_{3}langle 001rangle$$ / $$rm TiNlangle 001rangle$$ / $$rm Silangle 001rangle$$ and their in-plane relationship $$rm TiO_{2}{110}$$ // $$rm SrTiO_{3}{100}$$ // $$rm TiN{100}$$ // $$rm Si{100}$$. The crystalline quality of TiO$$_{2}$$-anatase was examined by the rocking curve analysis. The composition of the thin film packaging was characterized by Rutherford backscattering spectrometry (RBS) using 2.0 MeV $$^{4}$$He beam.

28 (Records 1-20 displayed on this page)