Nanocrystalline ZnS thin films by chemical bath deposition method and its characterization

Zinc sulfide is a wide band gap semiconductor with a range of potential applications in optoelectronic devices. ZnS nanocrystalline thin films are prepared by chemical bath deposition on glass substrates. The chemical bath is an aqueous solution of zinc chloride, thiourea, ammonia and hydrazine. Governing factors related to the growth condition were the concentration of precursor solution, growth temperature, concentration of aqueous ammonia and growth duration. The structural and the surface topography of ZnS films have been investigated by x-ray diffraction and scanning electron microscope. The effect of annealing is studied. The x-ray diffraction study reveals that both powder and thin films are polycrystalline in nature and have a composition corresponding to the cubic structure [beta-ZnS]. The films are very close to ZnS stoichiometry and no organic compounds, Zn(OH)2 or ZnO species were observed as impurities. As it is also revealed from x-ray diffraction analysis, the average size of these nanocrystallites is about 3?nm using Scherrer formula. SEM characterization shows that the sample surface consisted of small uniform grains and was free from pinholes. Obviously, it is evident that aggregation of grains on the substrate forms the thin film. The films showed a high transmission and a wide band gap of 3.83?eV. This value is larger than the typical value of the bulk ZnS (similar to 3.6?eV), probably due to the quantum size effect as expected for the nanocrystalline nature of the films. The wide band gap of these films makes it possible to use them as window layer for solar cells. Copyright (c) 2012 John Wiley & Sons, Ltd.