Comparisons of structural and optical properties of ZnO films grown on (0 0 0 1) sapphire and (0 11¯2) sapphire by low-pressure MOCVD

ZnO films were grown on (0 0 0 1) orientation (C-plane) and (0 1 ¯ 1 2) orientation (R-plane) sapphire substrates by low-pressure metalorganic chemical vapor deposition (MOCVD). The crystallinity, surface morphology and optical properties of ZnO films on C and R sapphires were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectrum and transmission spectrum, respectively. The XRD patterns of the films indicated that ZnO grew on C sapphire with a (0 0 0 2) orientation, while (1 1 2 ¯ 0) ZnO grew on R sapphire. The epitaxial relationships of the two films were determined by X-ray θ−2 θ and ϕ scans. The SEM images exhibited that the ZnO film grown on C sapphire had a columnar morphology, and that the ZnO film on R sapphire possessed a smooth and dense surface. The room temperature PL spectra showed that both of the films had a good optical quality, but the intensity of the near band-edge emission (NBE) peak of the ZnO film on C sapphire was more intense than that of the film on R sapphire. Besides, the transmission spectra showed that the two ZnO films were highly transparent in the visible region.