High-quality ZnO thin films were deposited on 6H-SiC substrates using metal-organic chemical vapor deposition system. The physical properties of as-prepared ZnO layers under various oxygen flow rate were thoroughly studied. An increase in the O/Zn ratio yielded a decrease in growth rate. The experimental results also indicated that the size of ZnO nanoparticles, lattice constant and compressive stress inside the films displayed a regular variety as a function of O-2-flow rate. In addition, with increase of oxygen discharge, the position of deep-level emission in photoluminescence spectra demonstrated a significant shift, with transformation from oxygen vacancy to zinc vacancy. The qualitative calculation from X-ray photoelectron spectroscopy data showed that higher O-2-flow rate was able to promote O-Zn bond formation and reduce the number of oxygen vacancies. (C) 2012 Elsevier B.V. All rights reserved.