In order to decrease the free-electron concentration and increase the crystalline quality, zinc oxide (ZnO) thin films were deposited on sapphire (0 0 0 1) substrates by oxygen plasma-assisted pulsed laser deposition (PLD). ZnO films showed higher oxygen composition, stronger diffraction intensity of the (0002) direction, and larger grain size with regular hexagonal grain shape. The free-electron concentration was decreased greatly from similar to 10(19) to similar to 10(14) cm(-3) and the Hall mobility was increased from 6.8 to 37 cm(2) V-1 S-1. Furthermore, the intensity of the resonant Raman scattering and ultraviolet photoluminescence emission was increased. This enhancement of the crystalline, electrical and optical quality would be attributed to the increase of high activity oxygen density introduced by the plasma oxygen source. (c) 2007 Published by Elsevier B.V.