ZnO thin films were deposited on Si(100) and quartz glass substrates via metal organic chemical vapor deposition (MOCVD) using a diethyl zinc (DEZ) precursor and oxygen. The effects of the substrate temperature and direct/indirect plasma enhancement on the growth rate, preferred orientation, and transparency were investigated. From the Arrhenius plot of the deposition rate against the substrate temperature, it was found that the activation energy of the surface reaction was 38.35 kJ/mol. Below 300 degrees C, amorphous films were obtained, while ZnO films deposited above 300 degrees C showed a very strong preference for (002) plane orientation. The optical transparency of the films deposited at various experimental conditions showed good quality above 85%, and the bandgap of the films decreased with the substrate temperature in the range of 3.93-4.14 eV. It is assumed that mild energetic reactive radicals in the indirect plasma region are more effective for the MOCVD process than highly energetic ionic particles in the direct plasma region. (C) 2011 Elsevier B.V. All rights reserved.