Effect of Cd/S ratio on growth and physical properties of CdS thin films for photosensor application

In the present work, we have successfully deposited cadmium sulfide (CdS) thin films with quantum dot size on a silica glass substrate by using simple and commercial chemical bath deposition (CBD) with varying the concentration of the solution at ~ 50 °C bath temperature, where we found that the deposition parameters such as the precursor ratio of cadmium and thiourea strongly influence the morphology, physical properties, and photoresponse. There has been a disparity in the proportion of the equivalent elements of the precursors, where the stoichiometric ratio of Cd/S of the precursor was changed, which allows us to understand more about the conditions and influences on growth. There was a match when comparing standard Joint Committee on Powder Diffraction Standards (JCPDS) data with the study of X-ray diffraction and confirming the formation of a hexagonal crystal structure for CdS where is observed the size of the crystal varied and it was found that the estimated average of the CdS varied with the varying concentration and resulted in the least crystallite size of ~ 2.9 nm for the ratio of 0.01 M for cadmium and 0.02 M for sulfur. The field emission scanning electron microscopy (FE-SEM) images show the formation of nanosheets having micrometer-sized petals which got uniformity with varying Cd/S ratio. It can be seen absorption spectra near band edge ~ 400 nm with a slight deviation and presence of an excitonic peak for all samples with an estimated bandgap of CdS Quantum Dot (QD) thin films found to be varying from ~ 3.124 to ~ 3.11 eV. The photosensitivity was calculated for all CdS QD thin films and it was found that the photosensitivity increases with an increase in the Cd/S ratio.