Effects of post-thermal annealing on the optical constants of ZnO thin film

ZnO thin film was deposited onto (0 0 0 1) sapphire substrate by a sol–gel method. The as-prepared film was annealed at different temperatures from 600 to 950 °C in argon ambient. Transmittance spectra were used to determine the optical constants of the annealed ZnO film, and the effects of the annealing temperature on the optical constants were investigated. Transmittance measurement shows that the absorption edge blueshifts when the annealing temperature is below 750 °C while redshifts when the annealing temperature exceeds 750 °C. With increasing the annealing temperature, the optical constant of ZnO film decreases in the ultraviolet region while increases in the visible region.