Studies on the ZnxCo1−xS thin films: A facile synthesis process and characteristic properties

Abstract

We have synthesized a series of ZnxCo1−xS (0 ≤ x ≤ 0.4) thin films via the facile and industry preferred chemical deposition. Under the pre-optimized conditions (temperature = 80 ± 0.5 °C, substrate rotation = 65 ± 2 rpm, pH = 9.0 ± 0.1 and duration = 90 min) the deposited films were physically hard, uniform, tightly adherent to the substrate support. As-grown CoS and ZnxCo1−xS thin films were analyzed for compositional analysis, structural determinations, morphological studies and optical measurements. Elemental analysis determined replacement of Co2+ ions from the CoS lattice by Zn2+ ions, while a trivial scattering in the virtually constant S-content was observed. Elemental analysis using X-ray photoelectron spectroscopy established chemical states of constituting elements as Co2+, Zn2+ and S2−. Hexagonal structure with growth orientation along <101> up to x = 0.25 was observed in the structural studies and above x = 0.25, change in growth orientation along <100> was detected. Enhancement in self-organized growth module ensued the formation of fuzzy microstructure. Improvement in the hillocks with the integration of Zn2+ into CoS host was countersigned in the surface topography. The optical transmission spectra of the CoS and ZnxCo1−xS thin films were analyzed to evaluate the absorption coefficient (α). A systematic increase in α has been found and can be attributed to the creation of more localized states within the band tails due to the existence of defects and disorders.