Cadmium sulphide thin films grown by CBD: the effect of thermal annealing on the structural, electrical and optical properties

Cadmium sulphide (CdS) thin films have been grown by the chemical bath deposition (CBD) tecnnique using cadmium sulfate and thiourea, as the Cd <SUP>2+</SUP> and S<SUP>2-</SUP> ion sources. The chemically deposited films are annealed in air at different temperatures to estimate the effect of the annealing on the structural, optical and electrical properties of the films. These films have been characterized by means of X-ray powder diffraction (XRD), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), four point probe technique and UV-Visible spectrophotometer. From the results it is seen that the electrical resistivity, activation energy and the optical energy band gap are strongly depend on the annealing temperature. The optical band gap energy decreased from 2.43 eV to 2.39 eV with increasing the temperature. The electrical resistivity shows a decrease with the temperature with a minimum of 1.79×10<SUP>3</SUP> Ω-cm at 800 K for the annealed film at 473 K. However, the electrical resistivity shows an increase for 573 K< T < 773 K. With increasing the annealing temperature, the activation energy of the films decreased from 0.23 eV to 0.13 eV at low temperature region, and from 0.67 eV to 0.48 eV at high temperature region. The activation energies obtained from the absorption and resistivity measurements are compared. Also, the temperature coefficients of electrical resisitivity are determined to be between -2.02×10<SUP>-3</SUP>K<SUP>-1</SUP> and -1.72×10<SUP>-3</SUP> K <SUP>-1</SUP>.