ZnO thin films were prepared on Si(0 0 1) substrates using a pulsed laser deposition (PLD) technique and then their growth and properties were investigated particularly as a function of ambient O-2 pressure during film growth. It was found that the microstructure, crystallinity, orientation and optical properties of the films grown are strongly dependent on the O-2 pressures used. Completely c-axis oriented ZnO films are grown in a low O-2 pressure regime (5 X 10(-4)-5 X 10(-2) Torr), whereas a randomly oriented film with a much lower crystallinity and a rougher grained-surface is grown at an O-2 pressure of 5 X 10(-1) Torr. This deterioration in film quality may be associated with the kinetics of atomic arrangements during deposition. Our results suggest that ambient O-2 pressure is an important processing parameter and should be optimized in a narrow regime in order to grow a ZnO film of good properties in PLD process. (C) 2003 Elsevier B.V. All rights reserved.