Influence of electroplating temperature on the characteristic properties of zinc sulphide

Abstract

The effect of deposition temperature on the material and electronic properties of ZnS layers grown using a two-electrode electroplating configuration was explored and reported. The aqueous electrolyte from which ZnS layers were deposited contains 0.2 M ammonium thiosulphate ((NH4)2S2O3) and 0.2 M zinc sulphate monohydrate (ZnSO4 · H2O). Deposition temperatures of 30 °C, 55 °C and 80 °C were utilised. The electroplated thin-films were deposited on glass/fluorine-doped tin oxide (FTO) substrate and characterised for their structural, optical, morphological, compositional and electrical properties using x-ray diffraction (XRD), UV-Visible spectrophotometer (Optical absorption), Scanning electron microscopy (SEM), energy-dispersive x-ray analysis (EDX), Photoelectrochemical (PEC) cell measurements and DC conductivity measurements techniques. The XRD results indicate that the electroplated ZnS layers at 30 °C are polycrystalline with the dominant orientation along the ZnS(111)C plane. The XRD micrograph shows the presence of ZnO and unreacted Zn diffractions and amorphisation of the ZnS layers after heat treatment. The readings and estimations made from the UV-Visible spectrophotometric data depict a transition from a bandgap of ∼3.6 eV for the ZnS layers grown at 30 °C to ∼3.1 eV for layers grown at 80 °C. The ∼3.6 eV and ∼3.1 eV obtained bandgaps correspond to the bulk bandgaps of ZnS (of ∼3.7 eV) and ZnO (of ∼3.7 eV), respectively. PEC cell measurements show that the grown ZnS layers are n-type and the magnitude of the PEC signal varies with an increase in the deposition temperature. The DC conductivity measurements revealed that the conductivity of the ZnS layers is between (2 and 6) ×10−4 Ω−1 cm−1. There was a gradual increase in the ZnS layer conductivity as the deposition temperature increased.