Thickness and annealing effects on the optoelectronic properties of ZnS films

ZnS films were prepared with different thicknesses by electron beam evaporation on glass substrates. The films were annealed in air atmosphere at different annealing temperatures and times. The x-ray diffraction patterns indicate that the increase in film thickness resulted in good crystallinity of the ZnS film. The ZnS film transforms to mixed ZnS and ZnO upon annealing at 500 degrees C. The optical band gap (E(g)) values decrease from 3.70 to 3.43 eV as the thickness increases from 50 to 400 nm. The transmittance is affected strongly by annealing. Annealing at 400 degrees C enhances the visible range transmittance and the quality of the film. The E(g) values are not affected by the annealing time at 400 degrees C, while the refractive index decreases with increasing annealing time. The figure of merit revealed that the ZnS film annealed at 400 degrees C and coated with 8 nm zinc top layer is the best candidate for use as transparent conductive electrodes.