Baljinder Singh^1,, Rekha Rani¹

Silver (Ag, 1%) and tin (Sn, 1%) doped nanocrystalline cadmium sulfide (CdS) thin films were deposited on fluorine-doped tin oxide (FTO) glass substrates using vacuum evaporation aided by inert gas condensation (IGC) at room temperature (300 K). A hexagonal wurtzite phase with preferential orientation along the (002) plane and high crystalline purity was established by X-ray diffraction and Raman spectroscopy. Optical transmission investigations exhibited a red shift in the band gap to 2.23 eV (Ag) and 2.25 eV (Sn) from bulk CdS (2.42 eV) due to dopant-induced defect states resulting in band tailing. Electrical characterisation exhibited Schottky-type diode behaviour with increased rectification ratio and decreased series resistance for Ag-doped films. Ag-doped and Sn-doped devices illustrated better short-circuit current and fill factor from photovoltaic analysis, and double the sensitivity with ultrafast rise time of photoresponse (rise time ≈ 1.74 µs) in Sn-doped films. The results demonstrate dopant-dependent optimisation of structural and optoelectronic properties in nc-CdS films and suggest Ag doping for photodetectors with high sensitivity and Sn doping for ultrafast optoelectronic switching devices.

nanocrystalline, vacuum evaporation, Schottky-type diode, photodetector, optoelectronic switching devices