Effects of citric acid on properties of single phase CuAlO2 thin films derived by chemical solution deposition

Single phase CuAlO2 thin films were first successfully prepared on (0 0 0 1) sapphire substrates by chemical solution deposition method. Additionally, in order to improve the transmittance and conductivity of single phase CuAlO2 thin films, effects of citric acid as additive on phase structure, morphology and optical–electrical property of CuAlO2 thin films were investigated. Appropriate contents of citric acid do not inhibit the formation of single phase CuAlO2 thin films, and are also in favor of improvement of transmittance. Excessive citric acid not only introduces secondary phases, but also deteriorates the quality of the film surface. The mean transmittance in visible region is approximately 50% in the film prepared with 5 unit contents of citric acid and its direct and indirect optical band gaps are 3.24 eV and 1.8 eV, respectively. The films with or without citric acid behave like semiconductors. The resistivity and the activation energy of the film prepared with 5 unit contents of citric acid are evaluated as 2.5 × 102 Ω cm at 290 K and 300.5 meV, respectively.