Influence of annealing on properties of ZnO films grown via plasma-enhanced MOCVD

The structural and the optical properties of ZnO films with high quality grown via plasma-enhanced metallorganic chemical vapour deposition (MOCVD) on C-plane sapphire substrate were studied. The crystallinity and the optical properties of the films, which were annealed in oxygen plasma atmosphere, are greatly improved. The structure, the band gap and the binding energy of O_1s electrons, and the molar ratio of O to Zn were determined by X-ray diffraction (XRD), photoluminescence (PL) and X-ray photoelectron scan methods. For both the annealed and the as-grown films, the exciton peak features were observed at room temperature. The band-edge photoluminescence of the annealed film is much stronger than that of the as-grown film, and the exciton peak relating to the deep level at 439 nm disappears. The molar ratio of O to Zn in the annealed film is 0.91, while it is 0.78 for the as-grown film.