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Characterization of grain boundary properties in BaSi2 epitaxial films on Si(111) and Si(001) by Kelvin probe force microscopy

Masakazu Baba1, Sadahiro Tsurekawa2, Kotaro Nakamura1, Du Weijie1, Shintaro Koike1, Kaoru Toko1, Kosuke O Hara3, Noritaka Usami3,4, Takashi Suemasu1,4 1University of Tsukuba, Tsukuba, Japan /2University of Kumamoto, Kumamoto, Japan /3University of Tohoku, Sendai, Japan /4JST-CREST, Chiyoda-ku, Japan

Characterization of grain boundary properties in BaSi2 epitaxial films on Si(111) and Si(001) by Kelvin probe force microscopy: Masakazu Baba1, Sadahiro Tsurekawa2, Kotaro Nakamura1, Du Weijie1, Shintaro Koike1, Kaoru Toko1,Kosuke O. Hara3, Noritaka Usami3,4, and Takashi Suemasu1,4 1University of Tsukuba, 2University of Kumamoto, 3University of Tohoku, 4JST-CREST, Japan Semiconducting BaSi2 has preferable features for high-efficiency thin-film solar cells. In the 2012 PVSC, we have presented internal quantum efficiency exceeding 60% for 0.4-mm-thick BaSi2 film on Si(111). This year, we investigated the grain boundary (GB) character of BaSi2 by Kelvin prove force microscopy (KFM), and concluded that the GBs do not work as recombination centers for holes, minority carriers, in undoped n-type BaSi2 films. In order to study GBs character, we employed KFM, and evaluated potential distribution around the GBs in a-axis-oriented BaSi2 epitaxial films on Si(111) and Si(001) grown by molecular beam epitaxy. Undoped BaSi2 films show n-type conductivity of electron concentrations about 1016 cm-3. GBs for BaSi2 on Si(111) have a higher electrostatic potential than the grain interior, meaning that positive charges at the GBs result in a downward band bending. Thus, the GBs do not work as trap centers for holes in n-BaSi2. The average barrier height fGB is approximately 30 meV. On the other hand, GBs have a lower potential than grain interior in case of BaSi2 on Si(001), and the GBs have a upward convex band structure. Thus they are likely to work as trap centers for holes. The fGB is approximately 50 meV along BaSi2[010], while that is approximately 30 meV along BaSi2[001]. The difference in the band bending at the GBs for BaSi2/Si(111) and BaSi2/Si(001) is attributed to the difference in crystal planes consisting of GBs: the GBs in BaSi2/Si(111) consist mostly of BaSi2{011} planes, while the GBs consist of several planes in BaSi2/Si(001).