ZnO films were deposited on thermally oxidized SiO2/p-type Si (100) substrates and glass substrates by DC magnetron sputtering using a metal Zn target. Three types of samples were prepared with various O-2/(Ar + O-2) ratios (O-2 partial pressure) of 20%, 50%, and 80%. The properties of these ZnO thin films were investigated using X-ray diffraction (XRD), optical transmittance, atomic force microscopy (AFM), and spectroscopic ellipsometry in the spectral region of 1.7-3.1 eV. The structural and optical properties of ZnO thin films were affected by O-2 partial pressure. Relationships between crystallinity, the ZnO surface roughness layer, and the refractive index (n) were investigated with varying O-2 partial pressure. It was shown that the spectroscopic ellipsometry extracted parameters well represented the ZnO thin film characteristics for different O-2 partial pressures. (C) 2012 Elsevier B.V. All rights reserved.