Zinc sulphide (ZnS) thin films were synthesised by chemical bath deposition technique without using complexing agent. A physicochemical study was realized on the growth solution composed of ZnCl 2 , KOH, and SC(NH 2 ) 2 . The bath solution was at 60°C and pH values of 11.5, 12, and 12.5 were selected for growing the material. The species distribution diagrams, and solubility curves show that the growth mechanism requires the presence of zinchydroxide ions, and alkaline pH for growing the ZnS. The physicochemical properties of the samples improve as the pH of the solution increases. Samples deposited at pH=12.5 present a cubic structure (sphalerite) and bandgap energy of 3.72 eV, consistent with bulk-ZnS. For comparison, additional chemical baths were prepared by using NH3 as complexing agent; however, the properties of those samples result inferior. This methodology was validated by depositing ZnS films at 40°C without the complexing agent, obtaining similar results.

A physicochemical analysis, based on the species distribution diagrams and the solubility curves, is proposed for CDB-ZnS films deposition. The effect of the temperature and the HS−/Zn(OH)42− ion concentrations on ZnS films formation are discussed. ZnS thin films were deposited by chemical bath deposition (CBD) technique at near ambient temperatures (25, 40 and 55°C) from ZnCl2/KOH/NH4NO3/SC(NH2)2 solutions. From the physicochemical analysis it was found that by increasing the bath temperature and the [HS−]/[Zn(OH)42−] ratio, better conditions for obtaining ZnS films of good quality are obtained. Chemical, stoichiometric, and structural characterizations of the deposited ZnS thin films are reported. The formation of ZnS and/or Zn(OH)2 compounds, was identified by X-ray photoelectron spectroscopy (XPS) analysis. The stoichiometric [S]/[Zn] ratio of films was measured in a range between 0.22 to 0.77. X-ray diffraction (XRD) results show amorphous structures for almost all the films, excepting for ZnS samples prepared with the high temperature and [HS−]/[Zn(OH)42−] ratio when a cubic sphalerite phase (111) preferential structure was identified. The bandgap energy of the ZnS samples changes from 3.4 to 3.7 eV when the [HS−]/[Zn(OH)42−] ratio is modified.

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