Effect of Different Sulfur Pressure Annealing on Properties of ZnS Thin Films by Sputtering

As a kind of wide-band gap semiconductor, ZnS has attracted extensive attention in recent years due to its excellent photoelectric performance, which has broad application prospects in solar cells, photocatalysts and sensors. In this paper, ZnS thin films were first deposited by RF magnetron sputtering, and then annealed at 600℃ and different sulfur pressures. The crystal structure, surface morphology, grain size, composition, transmittance and defects of ZnS thin films were analyzed by XRD, XRD, SEM, EDS, UV-vis transmission spectra, positron annihilation Doppler broadening spectroscopy (DBS). The results show that the crystallinity of ZnS films can be improved by annealing in sulfur atmosphere, and the optical band gap of ZnS films after annealing is 3.43-3.58 eV. When the sulfur pressure is higher than 0.49atm, the sulfur interstitial atoms in the ZnS and the elemental sulfur on the surface reduce the transmittance of the film in the visible region. The DBS results also showed that the defect concentration of ZnS films decreased gradually from the surface layer to the inner layer, and the defect of ZnS films decreased with the increase of sulfur pressure. At the same time, the 3γ annihilation also proves that the interior of the film was relatively dense, and the open porosity of the film will increase due to vulcanization. Adsorbed sulfur occupies the position of sulfur vacancy defect in the crystal through internal diffusion, which leads to the decrease of defect concentration and the improvement of film quality.