Influence of growth rate on microstructure and optoelectronic behaviour of ZnS films

Nanocrystalline ZnS films have been grown on glass substrates by close spaced evaporation at various deposition rates, with a constant substrate temperature of 300 C-degrees. The x- ray photoelectron spectroscopy studies revealed that nearly stoichiometric ZnS layers were grown at deposition rates in the range 20 - 30 angstrom s(- 1). The x- ray diffraction data confirmed the cubic structure of ZnS films for all the deposition rates. The surface morphological studies were made using an atomic force microscope, which indicated a rough surface and that the roughness increases with the deposition rate. The optical analysis showed that the layers grown at a deposition rate of 30 angstrom s(- 1) exhibited the highest optical transmittance of 82%. The optical band gap of the films varied in the range 3.63 - 3.54 eV with the change in the deposition rate. The effect of the rate of deposition on the photoluminescence characteristics was also studied, which showed an increase in luminescence intensity with the decrease in the particle size. The electrical properties of the layers were highly influenced by the deposition rate. The temperature dependence of electrical conductivity was measured and the activation energies were also evaluated.