Effect of deposition temperature on the morphological, optical, and photodetection properties of CdS thin films

The influence of deposition temperature on the structural, optical, dielectric, and UV–visible photo-sensing properties of CdS thin films was investigated. A cadmium dithiocarbamate single solid-source precursor was synthesized and confirmed by particle-induced X-ray emission (PIXE) to contain cadmium and sulfur. CdS thin films were deposited via metal–organic chemical vapor deposition (MOCVD) at temperatures between 360 and 450 °C and subsequently characterized using Rutherford backscattering spectroscopy (RBS), scanning electron microscopy (SEM), and UV–visible spectroscopy. RBS analysis revealed a temperature-dependent variation in thin film stoichiometry, with a decrease in the Cd/S ratio at higher deposition temperatures. SEM micrographs showed pronounced morphological evolution, including grain refinement and reduced porosity with increasing temperature. Optical measurements indicated strong absorption in the UV-visible region and a direct optical band gap that decreased from 2.40 to 2.34 eV with increasing deposition temperature, accompanied by an increase in Urbach energy. Dielectric analysis revealed dispersive behavior of the real and imaginary parts of the dielectric constant with photon energy, while optical conductivity exhibited strong photon-energy dependence. Photo-sensing measurements under mercury, fluorescent, and tungsten illumination showed peak photoresistance at wavelengths corresponding to the optical band gap, confirming band-edge-dominated photoresponse. Overall, the results establish deposition temperature as an effective parameter for tuning the optoelectronic and photo-sensing performance of MOCVD-grown CdS thin films, highlighting their potential for application in photodetectors and other optoelectronic devices.