ZnO:Zn phosphor thin films prepared by ion beam sputtering

Abstract

ZnO:Zn phosphor thin films used in field emission displays were prepared by ion beam sputtering. Postdeposition annealing of these films was performed at temperatures ranged from 100–1000 °C in N2 atmosphere. Several techniques, including Rutherford backscattering spectroscopy (RBS), x-ray diffraction, atomic force microscopy, Hall effect measurement, and photoluminescence spectra, were employed to characterize these films. RBS results showed there was an amount of excess Zn in the films. The as-deposited films were found to contain both amorphous and crystalline phases. The morphology of the films consisted of several structures. It was detected that the free carrier concentration of these films decreased by increasing annealing temperature, indicating the elimination of excess Zn. Meanwhile, the Hall mobility increased quickly if the annealing temperature exceeded 400 °C, showing the improved crystallinity. Two categories of photoluminescent peaks, ultraviolet/violet and blue/green, were detected in ZnO:Zn films. The singly ionized oxygen vacancies were responsible for the visible luminescence which was strongly affected by the annealing processes. The possible reasons may include recovery of structural defects, homogenization of the films, and evaporation of the excess Zn with different contributions at different temperature ranges.