An experimental and theoretical study on soft chemically grown CuS thin film for photosensor application

Abstract

Herein we report, the photosensitivity of in-situ chemical bath deposition (CBD) grown CuS thin film for the first time, also comparatively very short deposition time of 40min and much lower bath temperature i.e. 45°C are reported. The structural, surface topographical, optical, electronic and electrical properties of as-grown CuS thin film have been investigated. The XRD analysis revealed the formation of Orthorhombic (Covellite) structure with preferential growth along [113] direction having ~14nm average crystallite size. Raman spectrum indicating a sharp peak at 474cm−1 confirms the formation of CuS covellite structure. Polycrystalline nature of the film has been confirmed from the concentric ring pattern obtained from TEM–SAED and AFM revealed the rough surface topography with RMS roughness of ~27nm. The bond lengths of Cu(1)-S(1) and S(1)-S(1) were obtained from the DFT calculations based on GGA approximation, suggest S-S bond is much stronger as compared to Cu-S bond; these results are in good agreement with the Raman result. The film shows higher absorbance in the visible region with a band gap of 2.2eV. The electrical properties show a drastic increase in current after light illumination of 50 W which increases with increasing light intensity and tends to attain a saturation state around 200 W. The highest photosensitivity of ~66% has been calculated for 200 W with fast response time of ~34s and a complete recovery. These results represent CuS thin films promising candidature for photosensor application.