Effect of annealing on the photoluminescence characteristics of ZnO thin films grown on the sapphire substrate by atomic layer epitaxy

High-quality ZnO thin films have been grown on sapphire substrates by the atomic layer epitaxy (ALE) technique using diethylzinc (DEZn) and H2O as reactant gases at substrate temperatures of 170 and 400 °C. In order to investigate the effect of annealing treatment on the optical properties of ZnO films, the films have been annealed at various annealing temperatures after deposition. After the annealing treatment the optical properties of ZnO thin films were characterized by photoluminescence (PL). A strong free exciton emission with a weak defect-band emission in the visible region was observed at room temperature (RT). Full width at half-maximum (FWHM) measurement of the free exciton emission of 67.54 meV have been made at room temperature. Based on the temperature dependence of the PL spectra in the temperature range from 10 K to room temperature it has been shown that the crystalline quality of the films increases as the annealing temperature increases. Also it shows that the best result is obtained when the sample is deposited at 170 °C and annealed at 1000 °C.