Chemical Design and Thin Film Preparation of p-Type Conductive Transparent Oxides

Chemical design to find a new transparent conductive oxide having p-type conductivity has been proposed. Following the chemical design, we have selected CuGaO₂ and CuAlO₂ as candidate materials. CuGaO₂ thin films were prepared on silica glass substrates by RF sputtering method. The optical band gap of the film was estimated to be 3.4 eV. Positive sign of Seebeck coefficient demonstrated the p-type conductivity of the film. The dc conductivity of the film was 5.6 × 10^–3S·cm^-1 and the activation energy was 0.22 eV at room temperature. Because of rough texture of the film, the observed conductivity was not an intrinsic property of the material. Further, CuAlO₂ thin films were prepared by laser ablation. The film deposited in O₂ atmosphere of 1.3 Pa at 690°C showed higher optical transmission in visible and near-infrared regions than previously reported. Contribution of Cu 3d components to upper edge of valence band in CuGaO₂ and CuAlO₂ were confirmed by photoemission spectroscopic measurements.