High-quality ZnO thin films on c-plane sapphire (Al2O3) substrates were prepared by plasma-molecular beam epitaxy (P-MBE). The influence of growth temperature on growth mode of ZnO was investigated. Real-time monitored by reflection high-energy electron diffraction (RHEED) images show that, below 500° C, ZnO thin film was grown by three-dimension (3D) growth mode. While the two-dimension (2D) growth mode was obtained above growth temperature of 650 ° C. Atomic force microscopy (AFM) images present that the surface morphology of ZnO thin film with (2D) growth is improved and X-ray rocking curves (XRC) indicate that the full width at half maximum (FWHM) of the ZnO (002) peak becomes narrow. From the photoluminescence (PL) spectra, ultraviolet (UV) emission peak exhibits obvious blue-shift for the samples grown at lower temperature, which is attributed to the effect of the quantum confinement arisen from small crystal grain sizes. The minimum carrier concentration of N = 7.66 x 10(16) cm(-3) was obtained in the ZnO thin films with the 2D grown, which is closed to that of bulk ZnO. © 2005 Elsevier B.V. All rights reserved.