ZnO films have been grown on Si(111) substrates by metal-organic chemical vapor deposition using diethylzinc and CO2 as precursors. The effects of growth temperature on growth rate, structure, and optical properties of the ZnO films were investigated in a temperature range between 450 and 700 °C. As growth temperature increased, the growth mode changed from kinetics-limited to mass-transfer-limited, and finally, to desorption-limited mode. Using the Arrhenius equation, the activation energy for the kinetics-limited growth mode was estimated to be 105 meV. The crystalline quality was also strongly dependent on growth temperature. With increasing growth temperature, the width of x-ray diffraction peaks decreases and the photoluminescence intensity enhances. Using CO2 as the oxygen source, we found that the optimal growth temperature was near 600 °C.