著者

Ito Keita Sanai Tatsunori Zhu Siyuan Yasutomi Yoko Toko Kaoru Honda Syuta Ueda Shigenori Takeda Yukiharu Saitoh Yuji Imai Yoji Kimura Akio Suemasu Takashi

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.103, no.23, pp.232403, 2013-12

被引用文献数

11 1

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We evaluated electronic structures and magnetic moments in Co3FeN epitaxial films on SrTiO3(001). The experimentally obtained hard x-ray photoemission spectra of the Co3FeN film have a good agreement with those calculated. Site averaged spin magnetic moments deduced by x-ray magnetic circular dichroism were 1.52 μ B per Co atom and 2.08 μ B per Fe atom at 100 K. They are close to those of Co4N and Fe4N, respectively, implying that the Co and Fe atoms randomly occupy the corner and face-centered sites in the Co3FeN unit cell.

著者

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

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.114, no.12, pp.123702, 2013-09

被引用文献数

15

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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.

著者

Baba Masakazu Tsurekawa Sadahiro Watanabe Kentaro Du W. Toko Kaoru Hara Kosuke O. Usami Noritaka Sekiguchi Takashi Suemasu Takashi

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.103, no.14, pp.142113, 2013-09

被引用文献数

29 3

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Potential variations around the grain boundaries (GBs) on the surface in undoped n-BaSi2 epitaxial films on Si(111) and Si(001) were analyzed using Kelvin prove force microcopy. The potentials were higher at GBs than those in the BaSi2 grains on Si(111). The average barrier height was approximately 30 meV at the GBs, indicating that the enhanced potentials repulse photogenerated holes so that the charge carrier recombination can be effectively reduced. In contrast, the potentials were smaller at GBs in the BaSi2 on Si(001), and the average barrier heights were approximately 30 and 50 meV along Si[1–10] and [110], respectively.

著者

Sanai Tatsunori Ito Keita Toko Kaoru Suemasu Takashi

出版者

Elsevier B.V.

雑誌

Journal of crystal growth (ISSN:00220248)

巻号頁・発行日

vol.378, pp.342-346, 2013-09

被引用文献数

5 1

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We formed CoxFe4−xN (0≤x≤2.9) epitaxial thin films on SrTiO3 (001) substrates by molecular beam epitaxy supplying solid Co and Fe and a radio frequency N2 plasma, simultaneously. The composition ratio of Co/Fe in CoxFe4−xN was controlled by changing the weight ratio of Co to Fe flakes in the crucible of the Knudsen cell used. Epitaxial growth of CoxFe4−xN thin films were confirmed by reflection high-energy electron diffraction and θ–2θ X-ray diffraction patterns. Magnetization versus magnetic field curves measured at room temperature using a vibrating sample magnetometer showed that the axis of easy magnetization was changed from [100] to [110] with increasing x in CoxFe4−xN.

著者

Khan M. Ajmal Hara Kosuke O. Nakamura Kotaro Du Weijie Baba Masakazu Toh Katsuaki Suzuno Mitsushi Toko Kaoru Usami Noritaka Suemasu Takashi

出版者

Elsevier B.V.

雑誌

Journal of crystal growth (ISSN:00220248)

巻号頁・発行日

vol.378, pp.201-204, 2013-09

被引用文献数

18 1

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We have successfully grown a-axis-oriented p-type BaSi2 films on Si(111) by in situ boron (B) doping using molecular beam epitaxy (MBE). The hole concentration in B-doped BaSi2 was controlled in the range between 1017 and 1019 cm−3 at room temperature by changing the temperature of the B Knudsen cell crucible. The acceptor level was estimated to be approximately 23 meV.

著者

Toko Kaoru Fukata Naoki Nakazawa Koki Kurosawa Masashi Usami Noritaka Miyao Masanobu Suemasu Takashi

出版者

Elsevier B.V.

雑誌

Journal of crystal growth (ISSN:00220248)

巻号頁・発行日

vol.372, pp.189-192, 2013-06

被引用文献数

15 4

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High-quality crystalline Ge thin films on low-cost glass substrates are desired to reduce the fabrication cost of high-efficiency tandem solar cells. We applied an Al-induced crystallization technique to amorphous-Ge films (50-nm thickness) on SiO2 glass substrates. The annealing temperature of the sample strongly influenced the grain size and the crystal orientation in the grown polycrystalline Ge layers: low annealing temperatures resulted in large grains and high (111)-orientation fractions. As a result, annealing at 325 °C provided 98% (111)-oriented grains with average diameters of 30 μm. Moreover, the grown Ge layers could be used as an epitaxial template for chemical vapor deposition. This large-grained Ge film on a SiO2 substrate appears promising for use as a Ge light-absorbing layer, as well as an epitaxial buffer layer for group III–V compound semiconductors.

著者

Ootsuka Teruhisa Suemasu Takashi Chen Jun Sekiguchi Takashi Hara Yoshiaki

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.92, no.19, pp.192114, 2008-05

被引用文献数

14

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We have evaluated the lifetime and diffusion length of photogenerated minority carriers (holes) in single-crystalline n-type beta-FeSi2 bulk grown by chemical vapor transport. The diffusion length measured by optical-beam-induced current agreed well with that measured by electron-beam-induced current, that is, 51 and 38 µm, respectively, for samples annealed at 800 °C for 8 h. The decay curve of photoconductivity obtained by 1.31 and 1.55 µm light pulses was well fitted by assuming a carrier lifetime of approximately a few microseconds. The mobility of photogenerated minority carriers was estimated to be approximately 200–360 cm2/V s from the measured lifetime and diffusion length.

著者

Ootsuka Teruhisa Suemasu Takashi Chen Jun Sekiguchi Takashi

出版者

American Institute of Physics

雑誌

APPLIED PHYSICS LETTERS (ISSN:00036951)

巻号頁・発行日

vol.92, no.4, pp.042117, 2008-01

被引用文献数

13 15

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We have evaluated the diffusion length of minority carriers (holes) in single-crystalline n-type beta-FeSi2 bulk grown by chemical vapor transport by means of electron-beam-induced current (EBIC) technique in the edge-scan configuration. The EBIC line-scan data showed a clear exponential dependence of distance from the Al electrode. The diffusion length was estimated to be 20 µm at room temperature, and increased upon high-temperature annealing, reaching approximately 30 µm after annealing at 800 °C for 8 h. This result explained the improvement of photoresponsivity in the Al/n-beta-FeSi2 Schottky diodes by high-temperature annealing.

著者

Ootsuka Teruhisa Fudamoto Yasunori Osamura Masato Suemasu Takashi Makita Yunosuke Fukuzawa Yasuhiro Nakayama Yasuhiko

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.91, no.14, pp.142114, 2007-10

被引用文献数

23 25

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We have clearly observed photoresponse properties in an Al/n-beta-FeSi2 structure using beta-FeSi2 single crystals grown by chemical vapor transport. A photocurrent is observed for photons with energies greater than 0.68 eV. It increases sharply with increasing photon energy and attains a maximum at approximately 0.95 eV (1.31 µm). The photocurrent originated from the photoexcited electrons in the Al and the band-to-band photoexcited carriers in the beta-FeSi2 located under the Al contact. The photoresponsivity increased upon high-temperature annealing, reaching 58 mA/W at 0.95 eV after annealing at 800 °C for 8 h.

著者

Sanai Tatsunori Ito Keita Toko Kaoru Suemasu Takashi

出版者

Elsevier B.V.

雑誌

Journal of crystal growth (ISSN:00220248)

巻号頁・発行日

vol.357, pp.53-57, 2012-10

被引用文献数

13

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We attempted to grow CoxFe4−xN epitaxial thin films on SrTiO3(001) substrates by molecular beam epitaxy supplying solid Co and Fe and a radio frequency N2 plasma, simultaneously. The composition ratio of Co/Fe in CoxFe4−xN was controlled by changing the weight ratio of Co to Fe flakes in the crucible of the Knudsen cell used. We confirmed epitaxial growth of CoxFe4−xN (0.4<x<2.9) thin films by reflection high-energy electron diffraction and θ−2θ X-ray diffraction patterns. The in-plane lattice parameter of the CoxFe4−xN films was almost the same as the out-of-plane lattice parameter, and they decreased with increasing Co composition, following Vegard's law.

著者

Okada Atsushi Toko Kaoru O. Hara Kosuke Usami Noritaka Suemasu Takashi

出版者

Elsevier B.V.

雑誌

Journal of crystal growth (ISSN:00220248)

巻号頁・発行日

vol.356, pp.65-69, 2012-10

被引用文献数

20

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We have fabricated poly-Si thin films on fused silica substrates by the Al-induced crystallization (AIC) method with SiO2 insertion layers of various thicknesses (0–20 nm). The growth morphologies of poly-Si layers were dramatically changed by the SiO2 thickness, i.e., thin layers (2 nm) provided high growth rates and (100) orientations, and thick layers (10 nm) provided low growth rates and (111) orientations. These results showed that the crystal orientation of AIC-Si significantly depends on the diffusion rate of Si atoms into the Al layer.