Consequence on Optical Properties of ZnS Thin-Film Deposited by RF Magnetron Sputtering with Varying Substrate Temperatures

Earth abundant and ecofriendly zinc sulphide (ZnS) is a direct wide band gap semiconductor material and applications of ZnS thin-films cover a large area including optoelectronic devices. As thin-films of ZnS are highly defective depending on fabrication process, prior to final target applications, properties of thin-films should be studied first. This study was motivated to apply ZnS thin-film as an alternative buffer layer in a chalcogenide based multilayer thin-film solar cell (TFSC) e.g. CZTS using a reliable and clean deposition technique. This study reports mainly on optical properties of ZnS thin-films with varying substrate temperatures. ZnS thin-films were deposited on soda lime glass (SLG) substrates using radio frequency (RF) magnetron sputtering. Room temperature (RT), 150° C, 300° C were taken as substrate temperature variants with RF power and argon (Ar) flow rate remained fixed at 100W and 20 SCCM respectively for all depositions. Structural properties were confirmed by XRD and optical properties were probed by UV-Vis NIR spectroscopy. It was found from structural studies that most of the films were crystallographically cubic type lattice, oriented along (111) plane with Bragg's diffraction angle at 28.95°. The average optical transmittance were found around 87% (invisible and near infrared regions of spectrum). The optical band gaps as obtained were in decreasing nature from 3.96eV to 3.71eV as substrate temperature increased from room temperature to 300°C, were in good agreement with Urbach energy analysis. Although the findings of optical properties are potentially positive, prior to apply ZnS thin-film as a buffer layer in full TFSC fabrication, more investigations will be required on electrical and morphological properties with the same investigated recipe.