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The Effect of Thermal Annealing on the Optical Band Gap of Cadmium Sulphide Thin Films, Prepared by the Chemical bath Deposition Technique
Cadmium sulphide thin films have been prepared by the chemical bath deposition technique (pH 11, 70oC). Two different sets of films were prepared under varied conditions and concentrations of their ions sources (Cd2+ from cadmium nitrate, S2- from thiourea) and Na2EDTA as a com-plexing agent. A UV mini Schimazu UV –VIS Spectrophotometer was used to determine the opti-cal absorbance of the films as a function of wavelength at room temperature over the wavelength range 200 – 600 nm. The samples were then thermally annealed for thirty (30) minutes, at tem-peratures of 100°C, and 200°C, after which the absorbance of the films were again recorded. The band gap values obtained for the sample with 0.5 M CdS as deposited, annealed at 100oC and annealed 200oC were 2.1 eV, 2.2 eV and 2.3 eV respectively. Whilst the values obtained for the sample 0.15M CdS as deposited, annealed at 100oC and annealed at 200oC were 2.0 eV, 2.01eV and 2.02 eV respectively. The increase in band gap with annealing temperature might be attributed to the improvement in crystallinity in the films.