Preparation of CuAlO2 thin films with high transparency and low resistivity using sol–gel method

CuAlO2 thin films were deposited on quartz substrates by sol–gel process using copper acetate monohydrate and aluminum nitrate nanohydrate as starting materials and isopropyl alcohol as solvent. The influence of annealing temperature on the film structure and the phase evolution of CuAlO2 films were investigated, so as to obtain CuAlO2 films with superior performance. The phase compositions of the films were dependent on the annealing temperature. The films annealed at temperatures below 400 °C were amorphous while those annealed above 400 °C were polycrystalline. The phases of CuO and CuAl2O4 appeared gradually with the increase of annealing temperature. When the heat treatment temperature was elevated to 900 °C, the uniform and dense films with single phase of CuAlO2 were obtained, with a resistivity of 15 Ωcm. The transmittance of the 310 nm-thick CuAlO2 film is 79% at 780 nm and the direct optical band gap is 3.43 eV.