F and Al co-doped zinc oxide thin films deposited by ultrasonic spray pyrolysis: Effects of substrate temperature on physical properties

In this study, F and Al co-doped ZnO (FAZO) films were prepared by ultrasonic spray pyrolysis combined with rapid thermal annealing treatment. The influence of substrate temperature (Ts) on the structure, morphology, and electrical and optical properties of the prepared FAZO films was systematically studied. The results showed the hexagonal wurtzite structure of all prepared FAZO films and the gradual changes in the preferred orientation of the films from (100) to (100) and (002) with increasing temperature. With increasing Ts, the diffraction peak of (002) became stronger, the morphology of the thin film changed from a mix of “rice-granular” small particles and “shell-like” large particles to flat and dense morphology, and the root-mean-square variation of the film’s particle size decreased. Furthermore, the resistivity decreased with an increase in Ts, and the film transmittance and optical bandgap increased significantly. The FAZO film prepared at 480 °C had the best photoelectric characteristics, with mobility of 22.9 cm2/(Vs), carrier concentration of 1.75 × 1020 cm–3, resistivity of 1.56 × 10–3 Ωcm, and over 85% average transmittance in the optical range of 400–1400 nm.