Optical and electrical studies of CdS thin films with thickness variation

Abstract

Cadmium sulphide (CdS) is the n-type, wide band gap II-VI semiconducting material by offering applications in photovoltaics. Among the range of applications offered by CdS thin films, it has found application as a window layer in second generation solar cells by creating photon traps, thereby quantum efficiency. Closed space sublimation (CSS) offers a trivial yet effective approach for the synthesis of thin films for solar cell applications at moderate temperatures. CdS thin films of controlled thicknesses were synthesized by CSS technique by varying exposure time. X-rays diffraction data of these thin films revealed polycrystalline nature with a preferred orientation along (002) direction. The scanning electron microscopy (SEM) based morphological studies showed grain size variation with an increase in thickness of deposited thin films in the range of 300–500 nm. The electrical studies revealed high resistivity of the order of 106 Ω-cm. Spectrophotometric studies performed for CdS thin films concluded with the calculation of the optical parameters such as refractive index, absorption coefficient employing the Swanepoel model, and energy band gap of ∼2.42 eV using the Tauc relation in addition to thin film thickness confirmation. The variations in thickness affect the structure, surface, optical (Khan et al. 2018), electrical properties.