Influence of anneal temperature in air on surface morphology and photoluminescence of ZnO thin films

The influence of anneal temperature in air ambient under atmospheric pressure on the surface morphology and photoluminescence of ZnO thin films grown on quartz substrate by RF sputtering has been investigated. The characterization of ZnO thin films was carried out by X-ray diffraction (XRD), atomic force microscope (AFM), DRUV-vis spectra (DRUV-vis), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS). XRD analysis shows the crystal quality of ZnO thin films becomes better after annealing in air. AFM results shows that the influence of anneal temperature on surface morphology is obvious. DRUV-vis results reveal that the transmittance increases in the region from 400 nm to 500 nm after annealing, without affecting the band gap. PL spectra of ZnO thin films by annealed at various temperatures consists of a near band edge emission around 380 nm and visible emissions due to the electronic defects, which are related to deep level emissions, which are generated during annealing process. The evolution of defects is analysed by PL spectra based on the energy of the electronic transitions. XPS results hint that the obvious change of oxygen species on the surface of ZnO, especially the increased oxygen vacancies with increasing the anneal temperature.