Annealing effect on the microstructure and photoluminescence of ZnO thin films

Zinc oxide thin films have been obtained by pulsed laser ablation of a ZnO target in O2 ambient at a pressure of 0.13 Pa using a pulsed Nd:YAG laser. ZnO thin films deposited on Si (1 1 1) substrates were treated at annealing temperatures from 400 °C up to 800 °C after deposition. The structural and optical properties of deposited thin films have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence spectra, resistivity and IR absorption spectra. The results show that the obtained thin films possess good single crystalline with hexagonal structure at annealing temperature 600 °C. Two emission peaks have been observed in photoluminescence spectra. As the post-annealing temperature increase, the UV emission peaks at 368 nm is improved and the intensity of blue emission at 462 nm decreases, which corresponds to the increasing of the optical quality of ZnO film and the decreasing of Zn interstitial defect, respectively. The best optical quality for ZnO thin films emerge at post-annealing temperature 600 °C in our experiment. The measurement of resistivity also proves the decrease of defects of ZnO films. The IR absorption spectra of sample show the typical Zn–O bond bending vibration absorption at wavenumber 418 cm−1.