Growth characteristics and optical properties of ZnO films epitaxially grown on Al2O3 (0 0 0 1) substrates at temperatures of T-g = 200-500 degreesC by metalorganic chemical vapor deposition were investigated. The in-plane orientation of ZnO unit cells was different for T-g = 200 degreesC and T-g greater than or equal to 300 degreesC. The surface morphology varied significantly: smooth surface with cracks at T-g less than or equal to 250 T-g facet and column growth at 300 degreesC less than or equal to T-g < 400 degreesC and grain surface for even higher growth temperatures. These results indicate that one can obtain flat ZnO films or ZnO rods by simply selecting the growth temperature. The crystalline and optical quality became better for higher growth temperatures. Mechanisms responsible for these observations are discussed. (C) 2003 Elsevier B.V. All rights reserved.