Optical properties of post-annealed ZnO:Al thin films studied by spectroscopic ellipsometry

In this paper, effects of the thermal annealing on the structural, electrical, and optical properties of Al-doped ZnO (ZnO:Al) thin films prepared by reactive radio-frequency sputtering were investigated. From the X-ray diffraction observations, the orientation of ZnO:Al films was found to be a c-axis in the hexagonal structure. The optical properties of the films were investigated by optical transmittance and spectroscopic ellipsometry characterization. Based on Tauc–Lorentz model, the optical constants of ZnO:Al films were extracted in the photon energy ranging from 1.0 to 4.5 eV. Our result showed that the refractive index and extinction coefficient of the films changed consistently with annealing temperature.