Surface passivation of GaAs semiconductor materials has been studied t o improve surface stability.An ultra-thin (~8nm) passivation layer of ZnO on GaAs was prepared by RF deposition method to control the interface trap densities and to prevent the Feimi level pinning.The optical and passivation performance of ZnO film has be en investigated by photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS).An increase in intrinsic PL intensity u p to 112.5% and a decrease in impurity PL intensity down to 82.4% are observed after depositing ZnO films compared with unpassivated GaAs surface.XPS measurement results show that the atomic concentration ratio of Ga/As (originally ~1.47) has been modifie d to a value of ~0.94,indicating an improvement of the surface stoichiometry in GaAs,Ga-O,As-O bonding is found to get effecti vely suppressed in RF deposited ZnO/GaAs interface structures.Passivation enhancement mechanism is also discussed.Research result s indicate that an ultra-thin ZnO film deposited on the GaAs surface is a feasible choice for GaAs surface passivation .