Influence of annealing temperature on the microstructure and photoluminescence of ZnO films

ZnO thin films with strong c-axis prefered orientation have been successfully deposited on Si (100) substrate at 750 degrees C by using reactive radio frequency magnetron sputtering. The influence of annealing temperature ranging from 600 to 1000 degrees C on the microstructure and photoluminescence (PL) properties of ZnO films was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence measurement at room temperature. The XRD and TEM results show that the grain size of ZnO film increases and the residual stress in the film is tensile and remains constant at about 1 GPa with the increase of annealing temperature below 900 degrees C. After annealed at 1000 degrees C, the grain size decreases and the residual stress in the film changes into compressive with the value about - 2 GPa. The PL spectra of the ZnO films show two emission bands, namely that originating from ultraviolet (UV) exciton transition and the visible defect photoluminescence. The intensity of UV PL spectrum and the relative intensity of different exciton emission are dependent on the grain size and defects in the ZnO film. The red shift of UV PL spectrum results from the change of the relative intensity of different exciton emission with annealing temperature. The visible PL spectrum is sensitive to the change of annealing temperature. The relationship between PL spectra and microstructure and defects in the films is discussed.