A comprehensive study on Co-doped CdS nanostructured films fit for optoelectronic applications

This research explores the novel photo-response properties of cobalt (Co) doped cadmium sulfide (CdS) thin films developed using a facile and cost-effective spray coating technique. The microstructural parameters were evaluated using XRD patterns and the estimated values of crystallite sizes, lattice strains, dislocation densities and induced stress were found to be in the range of 16.1–25.9 nm, 5.9 × 10−3-3.4 × 10−3, 3.8 × 10−3-1.4 × 10−3 and 3.4–1.9 (GPa) for undoped and Co:CdS films, respectively. The optical band gap energies were found to be 2.369, 2.454, 2.469, and 2.501 eV for undoped, 1 wt. %, 3 wt. %, and 5 wt. % Co: CdS films, respectively using Tauc's plots. The values of extinction coefficient (k) and refractive index (n) were observed in the range of 0.45–0.69 and 2.72–3.05 for as-prepared thin films. Photocurrent (Iph)-applied voltage (V) characteristic of the prepared thin films was measured under visible light condition of low power densities (0.15, 0.25, 0.50, 1.57, 2.50 and 5.0 mW/cm2). A remarkable photosensitivity of 0.165–8.842 × 103 (mW/cm2) at 5.0 mW/cm2 was observed. Saturated surface resistivity of as-prepared thin films was measured for pure CdS, which decreases by increasing Co content. External quantum efficiency (EQE) and Detectivity (DET) were enhanced with Co contents. The values of EQE and DET were found to be 1.0 × 103-2.47 × 1012 and 9.88 × 1012 -2.41 × 1012 for 5.0 wt. % Co: CdS films, respectively at power densities (0.15, 0.25, 0.50, 1.57, 2.50 and 5.0 mW/cm2). Our findings proposed the major role of such prepared films in the fabrication of advanced photodetectors suitable for optoelectronic devices developments.