Baljinder Singh^1,, Mayank Arora², Krishan Kumar³

This work presents the fabrication and comprehensive characterization of a self-powered, high-speed photodetector based on an FTO/nanocrystalline CdS:Sn 5% heterojunction. Tin-doped CdS thin films were deposited onto FTO-coated glass substrates using thermal evaporation coupled with inert gas condensation. XRD analysis revealed the polycrystalline nature of the nc-CdS:Sn 5% thin films with peaks corresponding to the hexagonal CdS phase. Raman spectroscopy showed characteristic phonon modes of CdS, while FE-SEM displayed densely packed grains with uniform morphology. EDAX confirmed the elemental composition with Cd, S, and Sn in the desired stoichiometric ratios. The resulting device exhibited pronounced rectifying behavior in the dark, alongside significant photovoltaic effects under illumination. Key device metrics included a sensitivity of 0.25, a responsivity of 1.62 µA/W, and a detectivity of 1.51 × 10⁶ Jones at zero bias, measured under white light irradiation. Dynamic response evaluation revealed reproducible operation up to 700 Hz, with fast rise and fall times of 0.07 µs and 2.56 µs, respectively. These findings underscore the promising potential of the FTO/CdS:Sn 5% heterojunction for high-speed optical communication, self-powered optical switching, and advanced optoelectronic applications.

nanocrystalline CdS, FE-SEM, heterojunction, self-powered photodetector, optoelectronics