Effects of substrate temperature on the dielectric function of ZnO films

ZnO films were deposited by RF magnetron sputtering at the substrate temperature of 120 420°C. XRD measurements revealed the improvement of crystalline quality and grain size of the films with substrate temperature. The dielectric function of the films was determined by fitting the experimental transmission spectra with Tauc-Lorentz (TL) model and a single Lorentzian oscillator (SLO) dispersion function in the energy range of 15 eV. The optical properties of the ZnO films strongly depended on the substrate temperature. The optical band gap and the Penn gap of the ZnO films increased with the substrate temperature. The band gap of the ZnO films indicated a direct interband transition between the valence and conduction band, and the change of the in-plane film stress promoted the enhancement of the band gap. These results of the optical properties of the ZnO films might be very meaningful to the application in the window design in solar cells.