Heteroepitaxial ZnO epilayers were grown on Si(1 1 1) substrates using a vertical geometry atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) system. The growth temperature was varied from 550 degrees C to 650 degrees C in steps of 25 degrees C. The ZnO growth rate and surface morphology were strong functions of the growth temperature and ranged from similar to 0.16 mu m/h to 1.36 mu m/h. The surface morphology of the ZnO films changed from granular to sharp tips as the growth temperature increased. The effect of buffer thickness was also examined, and was found to have a strong effect on the optical properties of the ZnO. An optimized growth condition for ZnO epilayers was found at 625 degrees C, producing a FWHM in the room temperature photoluminescence (PL) spectrum of 4.5 nm and a preferred growth orientation along the (0 0 2) direction. Transmission electron microscopy images and selected area diffraction patterns showed excellent crystalline quality of both the buffer and ZnO overlayer. When non-optimized growth temperatures were employed, post-growth annealing was found to greatly enhance the ratio of band-edge to deep level emission. (C) 2009 Elsevier B.V. All rights reserved.