Structural and luminescent characteristics of non-stoichiometric ZnO films by various sputtering and annealing temperatures

ZnO thin films were prepared by reactive RF magnetron sputtering at various deposition temperatures. They were annealed in oxygen ambient at various annealing temperatures. The microstructures and photoluminescence characteristics of ZnO films were investigated. The grain size of the ZnO thin film that was deposited at room temperature (RT) after annealing exceeded that of the film that was deposited at 500∘C. Excess Zn atoms were considered to be present in the ZnO film that was deposited at RT, so the film was non-stoichiometric ZnO. No visible emission of either of the ZnO films deposited at the two temperatures was observed before annealing. Following annealing at high temperature, the green emission from the ZnO film that was deposited at RT was stronger than that of the film that was deposited at 500∘C. The relationship between the non-stoichiometry of the thin film and the visible emission was discussed. The luminescent centers that correspond to green emission are defects; the concentration of defects was higher in the ZnO thin film that was deposited at RT than in the film that was deposited at 500∘C.