Hafnium oxide (HfO2) films were prepared using a pulsed sputtering method and different O-2/(O-2 + Ar) ratios, deposition pressures, and sputtering powers. Spectroscopic ellipsometry (SE) and positron annihilation spectroscopy (PAS) were used to investigate the influence of the deposition parameters on the number of open volume defects (OVDs) in the HfO2 films. The results reveal that a low O-2/(O-2 + Ar) ratio is critical for obtaining films with a dense structure and low OVDs. The film density increased and OVDs decreased when the deposition pressure was increased. The film deposited at high sputtering power showed a denser structure and lower OVDs. Our results suggest that SE and PAS are effective techniques for studying the optical properties of and defects in HfO2 and provide an insight into the fabrication of high-quality HfO2 thin films for optical applications. (C) 2011 Elsevier B.V. All rights reserved.