Low temperature synthesis of wurtzite zinc sulfide (ZnS) thin films by chemical spray pyrolysis

Zinc sulfide (ZnS) thin films have been synthesized by spray pyrolysis at 310 °C using an aqueous solution of zinc chloride (ZnCl₂) and thioacetamide (TAA). Highly crystalline films were obtained by applying TAA instead of thiourea (TU) as the sulfur source. X-ray diffraction (XRD) analyses show that the films prepared by TAA contained a wurtzite structure, which is usually a high temperature phase of ZnS. The crystallinity and morphology of the ZnS films appeared to have a strong dependence on the spray rate as well. The asymmetric polar structure of the TAA molecule is proposed to be the intrinsic reason of the formation of highly crystalline ZnS at comparatively low temperatures. The violet and green emissions from photoluminescence (PL) spectroscopy reflected the sulfur and zinc vacancies in the film. Accordingly, the photodetectors fabricated using these films exhibit excellent response to green and red photons of 525 nm and 650 nm respectively, though the band gaps of the materials, estimated from optical absorption spectroscopy, are in the range of 3.5-3.6 eV.