High-quality c-axis-oriented single-crystal ZnO films have been successfully grown on the (0 0 0 2) sapphire substrate by the low-pressure metal organic chemical vapor deposition technique. The effect of doping and annealing on the optical and structural properties has been investigated by means of X-ray diffraction (XRD), photoluminescence (PL) spectrum and atomic force microscopy (AFM). Annealing at high temperature was found to enhance the intensity of the (0 0 0 2) XRD peak and decrease the c-axis oriented lattice constant. However, the (0 0 0 2) XRD peak for the N-doped sample shifted to a low degree due to tensile stress possibly caused by nitrogen doping. The green-yellow band emission was observed in the room temperature PL spectrum of the undoped sample while the blue band emission emerged in the PL spectrum of the N-doped one. Low-temperature PL spectrum of the ZnO films was dominated by a sharp bound exciton line. Possible causes to the above differences will be given and discussed. (C) 2002 Elsevier Science B.V. All rights reserved.