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A study of nano crystalline Cd1-XCoXS thin composite films deposited by a liquid phase chemical bath deposition

Santosh T.Mane, Pandurang C.Pingale, Shrishail S. Kamble, Vikram S. Karande and Lalasaheb P. Deshmukh

A modified liquid phase chemical bath deposition (LPCBD) process set for its deposition conditions was used to synthesize CdS and Cd1-x Cox S ternary thin films. The deposition was carried out from a complex liquid phase formed by equimolar volumes of cadmium sulphate, triethanolamine, thiourea and cobalt sulphate. With the appropriate concentration and volume (x) of cobalt sulphate the initial film deposition compositions (0 ≤ x ≤ 0.5) were chosen. The growth kinetics was studied for various deposition time, temperature, resulting bath pH and speed of the substrate rotation and the reaction mechanism is suggested. It has been found that good quality samples (thin, uniform, tightly adherent, smooth, and diffusely reflecting) with colour changing from orange red to dark chocolate are obtained at 56 0C, 80 minutes deposition time, 70 rpm and pH equal to 11. The film thicknesses were measured by an interference technique. The chemical composition of the deposits was determined by an EDS analysis technique and it revealed that the films are Cd-rich. The XRD analysis of the as-grown CdS (2θ = 200-800) showed hexagonal wurtzite structure with a good match of d-values, intensities of reflections and the lattice parameters with the JCPD data. With the introduction of Co+2 in the lattice of CdS, the interplanar distances and the lattice parameters (a and c) have been found to be decreased continuously with the increase in x up to a value of x=0.1. The ratio c/a is almost constant. The average crystallite size, as-determined using FWHM method, is in the nano-range and increases typically from 11.77 nm to 17.37 nm upto x=0.1, then decreases for higher values x. A homogeneous solid solution of the Cd1-x Cox S type has been observed for these composites up to a value of x equal to 0.1. Spectral studies were performed on these films in the range of wavelengths between 500 nm to 1300 nm. Absorption by the film material is high (104-105cm-1) and the estimated bandgap decreased from 2.42 eV to 1.94 eV as x was varied from 0 to 0.5. Electronic transitions are of the direct type (m ≈ 0.5).