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133 results on '"Baba, Masakazu"'

14. Hard x-ray photoelectron spectroscopy study on valence band structure of semiconducting BaSi2.

Author

Baba, Masakazu, Ito, Keita, Du, Weijie, Sanai, Tatsunori, Okamoto, Kazuaki, Toko, Kaoru, Ueda, Shigenori, Imai, Yoji, Kimura, Akio, and Suemasu, Takashi

Subjects
*VALENCE bands, *PHOTOELECTRON spectroscopy, *SEMICONDUCTOR research, *PHOTOVOLTAIC cells, *DIRECT energy conversion, *MOLECULAR orbitals
Abstract

The valence band structures of a 35-nm-thick BaSi2 epitaxial film on Si(111) have been explored at room temperature by hard x-ray photoelectron spectroscopy (HAXPES). The experimentally obtained photoelectron spectrum is well reproduced by first-principles calculations based on the pseudopotential method. The top of the valence band consists mainly of Si 3s and 3p states in BaSi2, suggesting that the effective mass of holes is small in BaSi2. This is favorable from the viewpoint of solar cell applications. The observed spectrum shifted slightly to the lower energy side due to n-type conductivity of BaSi2. The valence band top was observed at about 0.8 eV below the Fermi level in the HAXPES spectrum. [ABSTRACT FROM AUTHOR]

Published
2013
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15. Investigation of grainboundaries in BaSi2epitaxialfilms on Si(1 1 1) substrates using transmissionelectronmicroscopy and electron-beam-induced current technique

Author

Baba, Masakazu, Toh, Katsuaki, Toko, Kaoru, Saito, Noriyuki, Yoshizawa, Noriko, Jiptner, Karolin, Sekiguchi, Takashi, Hara, Kosuke O., Usami, Noritaka, and Suemasu, Takashi

Abstract

a-Axis-oriented undoped n-BaSi2epitaxialfilms were grown on Si(111) substrates by molecular beam epitaxy, and the crystalline quality and grainboundaries were investigated by means of reflection high-energy electron diffraction, X-ray diffraction, and transmissionelectronmicroscopy (TEM). The grain size of the BaSi2films was estimated to be approximately 0.1–0.3 μm, and straight grainboundaries (GBs) were observed in the plan-view TEM images. Dark-field TEM images under a two-beam diffraction condition showed that these GBs consist mostly of BaSi2 {011} planes. The diffusion length of minority carriers in n-BaSi2 was found to be approximately 10 μm by an electron-beam-induced current technique.

Published
2012

16. Effect of grain areas on minority-carrier lifetime in undoped n-type BaSi2on Si(111)

Author

Toko Kaoru, Du Weijie, Shimada Naoya, Ryota Takabe, Baba Masakazu, Kosuke O. Hara, Suemasu Takashi, and Usami Noritaka

Subjects
Materials science, Analytical chemistry, Carrier lifetime, Epitaxy, Layer (electronics)
Abstract

We have grown undoped n-BaSi2 epitaxial films with different grain sizes on Si(111) and characterized their minority-carrier lifetime, τ. We found that τ value in undoped n-BaSi2 did not depend on average grain area, but on surface condition. The samples with mirror surfaces had large τ of about 0.4 μs and those with cloudy surface small τ of about 8 μs. We tried to cap the sample surface in situ with a 3 nm Ba or Si layer in order to control the surface of BaSi2, and succeeded to intentionally form BaSi2 with large τ.

Published
2015

17. Investigation of surface potential distributions of phosphorus-doped n-BaSi2thin-films by kelvin probe force microscopy

Author

Toko Kaoru, Baba Masakazu, Takabe Ryota, Daichi Tsukahara, and Suemasu Takashi

Subjects
Kelvin probe force microscope, Crystal, Band bending, Materials science, Condensed matter physics, Transmission electron microscopy, Microscopy, Grain boundary, Scanning capacitance microscopy, Thin film
Abstract

We investigated the surface potential distributions around grain boundaries (GBs) in phosphorus (P)-doped n-BaSi2 thin-films by Kelvin probe force microscopy (KFM) and the crystal planes constituting GBs by transmission electron microscopy (TEM). By KFM measurements, it was found that the GBs in P-doped n-BaSi2 are different from those in undoped BaSi2; undoped n-BaSi2 has a downward band bending around the GBs with barrier heights of approximately 30 meV. In contrast, P-doped n-BaSi2 has an upward band bending with barrier heights of approximately 15 meV. TEM observation revealed that most of the GBs in P-doped BaSi2 are composed of BaSi2 (011)/(0-11) planes. This result is the same as that in undoped BaSi2.

Published
2015

45. p-BaSi2/n-Si heterojunction solar cells with conversion efficiency reaching 9.0%.

Author

Tsukahara, Daichi, Yachi, Suguru, Takeuchi, Hiroki, Takabe, Ryota, Weijie Du, Baba, Masakazu, Yunpeng Li, Toko, Kaoru, Usami, Noritaka, and Suemasu, Takashi

Subjects
SILICON crystallography, MOLECULAR beam epitaxy, SOLAR cells, ENERGY conversion, PHOTONIC band gap structures, SILICIDES
Abstract

p-BaSi2/n-Si heterojunction solar cells consisting of a 20 nm thick B-doped p-BaSi2 epitaxial layer (p = 2.2 × 1018cm-3) on n-Si(111) (ρ = 1-4 Ω cm) were formed by molecular beam epitaxy. The separation of photogenerated minority carriers is promoted at the heterointerface in this structure. Under AM1.5 illumination, the conversion efficiency η reached 9.0%, which is the highest ever reported for solar cells with semiconducting silicides. An open-circuit voltage of 0.46 V, a short-circuit current density of 31.9 mA/cm2, and a fill factor of 0.60 were obtained. These results demonstrate the high potential of BaSi2 for solar cell applications. [ABSTRACT FROM AUTHOR]

Published
2016
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