ZnO films were grown on Si (100) substrates at low pressure in a vertical metal-organic chemical vapor deposition reactor with different total gas velocity. The structure and photoluminescence property of the undoped ZnO films grown with different flow rates of N-2 eluting gas were investigated. The structure quality was improved as the N-2 flow rate increased. In addition, when the flow rate of N-2 eluting gas was higher than 1.4 slm, a new luminescence peak which was attributed to the N-related defect was detected at room temperature, besides the other two peaks near the band gap, which were due to radiation of the free exciton and the electron from the donor level to the valence band respectively, also appeared at low flow rate of N2 eluting gas. (c) 2006 Elsevier B.V. All rights reserved.