Influence of source-to-substrate distance on the properties of ZnS films grown by close-space sublimation

ZnS films were deposited on soda glass at various source-to-substrate distances by closespace sublimation. The influence of source-to-substrate distance on the structural and optical properties of the films was investigated. XRD spectra showed that films were crystalline in nature having cubic structure oriented mainly alogn (111) plan. The crystallinity of films increased with the source-to-substrate distance up to 40 mm. The crystallite size increases from 15.76 to 19.06 nm as the source-to-substrate distance increased from 5 to 40 mm. AFM data reveled that RMS roughness decreases and grain size of the film increases with the source-to-substrate distance. The optical transmittance in the visible range was about 70% for all films. The refractive index of a ZnS film decreases with increasing source-to-substrate distance. But source-to-substrate distance seems to have no effect on the energy bandgap and absorption edge of ZnS films. Moreover, it is shown that resisitivity of the ZnS films resuced significantly by Ag doping.