We have studied the evolution of defects as a function of depth in oxygen-deficient and -surplus ZnO thin films using cathodoluminescence, photoluminescence, Rutherford backscattering spectroscopy/ion channeling and Auger electron spectroscopy. Depth resolved cathodoluminescence indicates three types of defects are present in the films and their densities are strongly dependent on the film stoichiometry as well as depth. In addition, we also have observed two different emission characteristics arising from the interface due to the different growth modes that occur at the early stage of the deposition. In the oxygen-deficient sample, growth begins with nucleation and coalescence that introduce a high density of defects at the interface. On the other hand, the deposition of oxygen-surplus film involves a two-dimensional layer-by-layer growth, which then transforms into the columnar growth mode. Our results imply the control of light emissions in ZnO can be made possible once the growth process is understood. (C) 2004 Elsevier B.V. All rights reserved.