Effect of sputtering process parameters on structural and optical properties of CdS thin films

We have studied the effect of sputtering process parameters; substrate temperature, deposition pressure and sputtering power on structural and optical properties of cadmium sulfide (CdS) thin films. CdS thin films were deposited on glass substrate by radio frequency (RF) magnetron sputtering technique at various sputtering process parameters. Deposited CdS thin films were characterized by using x-ray diffractometer (XRD), Field emission scanning electron microscope (FE-SEM), Energy dispersive x-ray spectroscopy (EDX), Atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and optical spectroscopy for their microstructural and optical properties, respectively. Crystalline hexagonal structured CdS thin films have been successfully achieved at 200 degrees C deposition temperature, 1.33 Pa deposition pressure and 50 W sputtering power. Optical constant, refractive index and extinction coefficient have been studied using spectroscopic ellipsometry for all optimized samples. Chemical bonding state of Cd (3d(5/2) & 3d(3/2)) and S (2p(3/2) & 2p(1/2)) have been confirmed using XPS spectra. The band gap of the optimized samples was analyzed using ellipsometry and UV spectrophotometer. The maximum root mean square (RMS) roughness of CdS films is found to be similar to 8 nm. The band gap of the optimized samples is achieved in the range of 2.3-2.5 eV. The successfully grown cytalline CdS thin films with higher bandgap, surface roughness, and higher refractive index can be used in solar cell and other optoelectronic devices.