EFFECTS OF BUFFER SALT CONCENTRATION ON THE DOMINATED DEPOSITION MECHANISM AND OPTICAL CHARACTERISTICS OF CHEMICALLY DEPOSITED CADMIUM SULFIDE THIN FILMS

Abstract

Effects of buffer salt concentration on the rate of deposition, dominated deposition mechanism and subsequently the structural, morphological, and optical properties of cadmium sulfide (CdS) thin films deposited by chemical bath deposition (CBD) on glass substrate were investigated. The precursors were chosen to be cadmium chloride (CdCl2) as the cadmium source, thiourea (CS(NH[Formula: see text]) as the sulfur source, ammonium nitrate (NH4NO3) as the buffer salt and ammonia as the complexing agent and the pH controller. The influence of the NH4NO3 concentration on the structure, morphology, film uniformity, stoichiometry and optical properties of CdS thin films was also studied by X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM), energy dispersive X-ray (EDX) spectroscope, uv–visible and photoluminescence (PL) spectroscopes. The XRD studies revealed that all the deposited films exhibited a (002)h/(111)c preferred orientation. The crystallite size was increased from 20[Formula: see text]nm to 30[Formula: see text]nm by the increase of concentration of NH4NO3 from 0.5[Formula: see text]M to 2.5[Formula: see text]M. The morphology of CdS thin films were agglomerated spherical particles consisted of smaller particles. The surface of thin films deposited at the NH4NO3 concentration of 0.5[Formula: see text]M was compact and smooth. The increase of the concentration of NH4NO3 decreased the packing density of the films. The optical band gap was in the range of 2.25–2.4[Formula: see text]eV, which was decreased by the decrement of packing density. The PL spectra showed two peaks centered at 400[Formula: see text]nm and 500[Formula: see text]nm which are attributed to violet and band-to-band emissions, respectively.