Physicochemical Analysis and Characterization of Chemical Bath Deposited ZnS Films at Near Ambient Temperature

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.