Preparation and Characterization of ZnS Thin Films Grown by Spin Coating Technique

Abstract

Spin coating technique was used to deposit zinc sulphide (ZnS) thin films successfully onto glass substrates and the effects of the number of spin times on the optical properties investigated. The morphology and structures of the prepared thin films were also confirmed. X-ray diffraction confirmed that spin coated ZnS films exhibited cubic structure, where reflections from (111), (220) and (311) are clearly visible with a preferential orientation along (111) plane. The calculated crystallite size for 1S sample from the XRD data is 8.8 nm. From the optical studies, the thin films exhibit good optical properties with relatively high transmittance (81 %) and low absorbance in the visible region. The transmittance decreases as the number of spin time increases, and this may be attributed to increase in thickness of the films. This feature is reflected in all the other optical parameters. The band gaps obtained ranged from 3.70 to 3.87 eV, which are relatively higher than the energy band gap of the bulk ZnS material (i.e., 3.65 eV) and it increases with increasing number of spin times. The SEM micrograph showed that the films deposited are uniform throughout the surface without voids. EDX analysis showed the presence of zinc and sulphur in the prepared films with percentages by weights of 78.2% and 6.0%, respectively, showing that the films are sulphur deficient.  These results therefore showed that the prepared ZnS films exhibit properties of materials that can be used as optoelectronic devices especially as window for photovoltaic cells.

Keywords: Zinc sulphide thin films; Spin coating technique; Optoelectronic properties; EDX; Surface morphology.