Optical and electrical properties of CuScO2 epitaxial films prepared by combining two-step deposition and post-annealing techniques

A CuScO2(0 0 0 1) epitaxial film with a thickness of a few hundred nanometers was successfully grown on an a-plane sapphire substrate by combining the two-step deposition and post-annealing techniques. The film was single-phase with a rhombohedral crystal structure and showed six-fold rotational symmetry in the basal plane, indicating that the film had a twinned domain structure. The orientation relationships of the film with respect to the substrate were CuScO2[3R](0 0 0 1)//sapphire(1 1 2¯ 0) and CuScO2[3R][1 1 2¯ 0]//sapphire[0 0 0 1]. The average optical transmittance of the film was higher than 60% in the visible/near-infrared regions, and the energy gap for direct allowed transition was estimated to be 3.7 eV. The p-type conduction of the film was confirmed by Hall measurement. The electrical conductivity, carrier concentration, Hall mobility, and Seebeck coefficient of the film at room temperature were 1.0×10−3 S cm−1, 4.5×1016 cm−3, 1.4×10−1 cm2 V−1 s−1, and +968 μV K−1, respectively. The activation energy estimated from the temperature dependence of the carrier concentration was 0.62 eV.