2017年第64回応用物理学会春季学術講演会

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21 合同セッションK「ワイドギャップ酸化物半導体材料・デバイス」 » 21.1 合同セッションK 「ワイドギャップ酸化物半導体材料・デバイス」

[15a-502-1~12] 21.1 合同セッションK 「ワイドギャップ酸化物半導体材料・デバイス」

2017年3月15日(水) 09:00 〜 12:15 502 (502)

古田 守(高知工科大)

10:45 〜 11:00

[15a-502-7] Electric Field Thermopower Modulation of BaSnO3 Epitaxial Film

〇(P)SANCHELA ANUPKUMAR VINODRAY1、OHTA HIROMICHI1 (1.RIES-Hokkaido Univ.)

キーワード:Wide bandgap oxide semiconductor materials and devices

Recently, electron doped BaSnO3 (S.G.: Pm-3m, Cubic perovskite structure, a=4.115 Å, Eg~3.1 eV) has attracted growing attention as a transparent oxide semiconductor. Since the conduction band of BaSnO3 is mainly composed of widely spread Sn 5s orbitals, BaSnO3 single crystal exhibits very high electron mobility at room temperature (~300 cm2 V−1 s−1). Although several researchers reported the effective mass to clarify the origin of such high mobility, the values are widely scattered from 0.06 to 0.6 m0. Here we report reliable effective mass, which can be clarified by the electric field thermopower modulation of BaSnO3 epitaxial films. We fabricated three-terminal thin film transistors on BaSnO3 epitaxial films, which were fabricated on (001) SrTiO3 single crystal by PLD followed by the thermal annealing at 1200 °C in air. Amorphous C12A7 film (~300 nm, εr=12) was used as the gate insulator. The sheet carrier concentration was modulated from 1011 to 1013 cm−2 by applying positive gate voltages. During the gate voltage application, we measured the thermopower of the BaSnO3 channel simultaneously as shown in Fig. The thermopower was modulated from 310 to 120 µV K−1, which is ~600 µV K−1 lower than that of SrTiO3 (m*=1.16 m0), demonstrating smaller carrier effective mass of BaSnO3 (m* < 0.2 m0). Further, we fabricated Nb-doped BaSnO3 epitaxial films (n~1021 cm−3) and clarified that the epitaxial films exhibit rather large the effective mass ~0.6 m0. Since thermopower strongly depends on the energy derivative of the electronic density of states at around the Fermi energy, these results clearly indicate that the energy dependence of the density of states of BaSnO3 is not simple parabolic in shape; this would be the reason of that the reported effective mass values are widely scattered.


Acknowledements: This work was supported by JSPS-KAKENHI (25246023, 25106007)