Effect of Ag-doping on microstructural, optical and electrical properties of sputtering-derived ZnS films

The ZnS:Ag nano-composite films with different Ag volume fractions (5, 10, 15 and 2 vol.%) were deposited on glass substrates by sputtering. The microstructures, optical and electrical properties of the as-deposited films were studied. XRD measurement shows that all films are polycrystalline with a microstructure of body-centered cubic phase belonged to ZnS. The samples in which Ag volume concentrations lower than 20 vol.% show a preferential orientation along the (2 2 0) direction. When Ag concentration reaches 20 vol.%, the intensity of the (2 2 0) peak belonged to ZnS decreases dramatically while the Ag (1 1 1) peak emerged. Based on our analysis, it can be noted that Ag can help the ZnS grains grow when Ag concentration is lower than 20 vol.%. However, the ZnS crystal growth is suppressed when Ag concentration is 20 vol.%. The refractive index of the samples decreases with the increase of Ag concentration while the extinction coefficient of the samples increases. The resistivity of the film reaches the minimum when Ag concentration is 20 vol.%, showing the electrical conductivity improvement of the composite film by doped Ag nano-particles.

► Ag concentration significantly influenced the grain growth of ZnS film.
► The refractive index of ZnS:Ag film obviously increases when Ag concentration is 20 vol.%.
► The film with high n implies the potential use for antireflective multilayer coating system.
► The extinction coefficient of the films indicates the plasma resonance at different wavelength.
► The film can be used for tunable emission wavelength in electroluminescent plat display devices.