Influence of sputtering power on the optical and electrical properties of Ti and Ga codoped ZnO thin films

Ti and Ga codoped ZnO (TGZO) thin films were deposited on glass substrates by radio-frequency magnetron sputtering technique using a sintered ceramic target of ZnO:TiO₂:Ga₂O₃ (97wt%:1.5wt%:1.5wt%) as sputtering source. The influence of sputtering power on structural, electrical and optical properties of the TGZO thin films was investigated by X-ray diffraction, four-point probe and UV-visible spectrophotometer. The results show that all the obtained films are polycrystalline with a hexagonal wurtzite structure and grow preferentially in the (002) direction. The sputtering power significantly affects the microstructure and electro-optical characteristics of the deposited films. The TGZO thin film prepared at the sputtering power of 200 W possesses the highest optoelectrical performance, which have the best crystal quality, the lowest resistivity, the highest average visible transmittance and the maximum figure of merit (1.22×10^-2 Ω^-1). Furthermore, the refractive index and extinction coefficient of the thin films were determined by the method of optical spectrum fitting, and the optical energy gaps were calculated using Tauc's relation.