Preparation and characteristics of chemical bath deposited ZnS thin films: Effects of different complexing agents

Zinc sulfide (ZnS) thin films were prepared on glass substrates by a chemical bath deposition technique using aqueous zinc acetate and thiourea solutions in a basic medium (pH ∼ 10) at 80 °C. The effects of different complexing agents, such as a non-complexing agent, Na3-citrate, and a mixture of Na3-citrate and ethylenediamine tetra-acetate (EDTA), on the structural, chemical, morphological, optical, and electrical properties of ZnS thin films were investigated. X-ray diffraction pattern showed that the ZnS thin film deposited without any complexing agent was grown on an amorphous phase. However, the ZnS thin films deposited with one or two complexing agents showed a polycrystalline hexagonal structure. No secondary phase (ZnO) was observed. X-ray photoelectron spectroscopy showed that all ZnS thin films exhibited both ZnS and ZnOH bindings. Field emission scanning electron microscopy (FE-SEM) images showed that ZnS thin films deposited with complexing agents had thicker thicknesses than that deposited without a complexing agent. The electrical resistivity of ZnS thin films was over 105 Ω cm regardless of complexing agents. The average transmittance of the ZnS thin films deposited without a complexing agent, those with Na3-citrate, and those with a mixture of Na3-citrate and EDTA was approximately 85%, 65%, and 70%, respectively, while the band gap was found to be 3.94 eV, 3.87 eV, and 3.84 eV, respectively.

► Thick ZnS thin films were successfully prepared by chemical bath deposition in a basic medium using less toxic complexing agents.
► Effect of different complexing agents such as no complexing agent, Na3-citrate and a mixture of Na3-citrate and EDTA on the properties of ZnS thin films was investigated.
► ZnS thin film deposited using two complexing agent showed the outstanding characteristics as compared to those using no and one complexing agent.