Comparative study of the structural, optical, and electrical properties of CuAlO₂ thin films on Al₂O₃ and YSZ substrates via chemical solution deposition

Single-phase delafossite CuAlO₂ thin films are deposited successfully on Al₂O₃ (001) and YSZ (100) substrates using the chemical solution method. X-ray diffraction data present that the CuAlO₂ film on the Al₂O₃ (001) substrate is epitaxial, whereas that on YSZ (100) is c-axis oriented; the same is also demonstrated by the HRTEM images and SAED patterns. Optical transmittance spectra exhibit that both films have high transparency in the visible region. However, in this region, the optical transmittance of the CuAlO₂ thin film deposited on (001) Al₂O₃ is inferior to that deposited on (100) YSZ. This optical anomaly can be attributed to surface scattering. Electrical transport measurements show that the resistivity of the film on (001) Al₂O₃ is one order lower than that on (100) YSZ, suggesting that in-plane orientation is significant in improving hole mobility.