Investigation of the Effect of Deposition Time and Annealing on the Structural and Optical Properties of Chemically Deposited ZnS Thin Films

Abstract

The Chemical bath deposition (CBD) technique was successfully used to deposit ZnS thin films. The effects of deposition time and annealing on the structural and optical properties of the obtained thin films were investigated by X-ray diffraction (XRD), and UV-Vis spectrophotometer, respectively. The XRD pattern for the as-deposited ZnS thin films deposited for 30 min showed three peaks at 2θ values of 28.75^o, 48.05^o, and 56.47^o corresponding to (111) (main peak), (220), and (311) reflection planes, indicating cubic structure. Comparing these peaks with that of the films prepared for 60 min, the latter have narrower widths, are more intense, sharper, and produce another weak peak at 2θ angle of 33.51^o. Post-annealing treatment results in even more intense and sharper peaks, with their width narrowing further, causing an improvement in the crystallinity. The grains detected from the SEM micrograph are well-defined with spherical shapes of varying sizes. The grain shape changes after annealing due to coalescence of the grains. According to the EDX result, Zn and S were present in the prepared film. The as-deposited films showed a maximum transmittance of 82.1% at the visible region, which increased to 89.2% after annealing. The optical energy band gap was found to be in the ranges of 3.58 - 3.75 eV and 3.41 - 3.73 eV for the as-deposited and annealed films, respectively, signifying that the energy band gap decreases with annealing.