Structural and optical properties of oxygen to argon flow ratio on the Zn_(0.98)Cr_(0.02)O thin films deposited by RF magnetron sputtering

摘要

High quality polycrystalline Zn_(0.98)Cr_(0.02)O thin films were deposited on glass substrates by RF magnetron sputtering technique. The effects of the gas-flow ratio of O_2/Ar on the crystallographic structures and optical properties of the thin films were systemically studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) and ultraviolet-visible transmittance measurements, respectively. XRD patterns show that all the films with hexagonal wurtzite structure have a preferred orientation with the c-axis perpendicular to the substrate plane. The results from SEM images reveal that the particle size of the Zn_(0.98)Cr_(0.02)O thin films firstly increases and then decreases with the increasing O_2/Ar gas flow ratio. In addition, these films have a high optical transmittance in the visible light region. And it is found that the band gap can be enlarged with the O_2/Ar gas flow ratio increasing. The PL measurements indicate that the intensity of the near band-edge emission increases gradually, whereas the intensity of the defect-level emission decreases with increasing O_2/Ar gas flow ratio. Based on these results, it can be concluded that the O_2/Ar ratios play a key role in controlling the stoichiometric and optical properties of the Zn_(0.98)Cr_(0.02)O thin films.