Effect of Ag incorporation on the microstructure and properties of ZnS thin films

In this study, ZnS thin films doped with different content of Ag were deposited on quartz glass substrates by RF magnetron sputtering technique and were annealed at 600 C in sulfur vapor. The crystal structure, grain size, surface morphology, composition, optical properties and defects of the doped ZnS thin films were analyzed by Xray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive Xray spectroscopy (EDS), UV-Vis spectroscopy and positron annihilation doppler broadening spectroscopy (DBS). The results showed that all films exhibited the cubic sphalerite structure with a preferred orientation along the (111) crystal plane, and the composition of the doped films were more consistent with the stoichiometric ratio compared to the undoped film. The grain size gradually increased as the Ag content grew, indicating the improvement of crystallinity of the ZnS thin films. Besides, the bandgap values of these ZnS films with good optical transparency in the visible region were decreased from 3.87eV to 3.53eV as the Ag content grew. DBS results also showed that the defect concentration of ZnS films gradually decreased from the surface to the inner layer, and the film defects decreased with the increase of Ag content. However, the types of defects changed when the Ag content increased. Furthermore, the results showed Ag also has an effect on the porosity of ZnS thin films.