Effect of Annealing on CdS-Bi₂S₃ Composite Thin Films Deposited by Modified Chemical Bath Deposition Technique

CdS-Bi₂S₃ composite thin films were deposited using the modified chemical bath deposition (MCBD) technique. The preparative parameters such as concentration, pH of cationic and anionic precursor, adsorption reaction and rinsing time, etc. were optimized to get good quality CdS-Bi₂S₃ composite thin films of terminal thickness 0.14 μm. These films were annealed in air at 300°C for 1h. The effect of annealing on structural, optical and electrical properties were studied. The XRD study reveals that the as deposited films turns from amorphous to polycrystalline after annealing and films are of CdS-Bi₂S₃ composite with individual CdS and Bi₂S₃ phases. Uniform surface morphology is been seen from SEM studies. From AFM, the grain size was observed to be ∼ 257nm. The elemental compositional analysis was done by EDAX studies, which showed that the composition of Cd, Bi, and S have nearly same composition for initial and final phase of the film. The optical band gap was estimated to be 2.15 eV and 2.00 eV for as-deposited and annealed films respectively which lies between band gaps of CdS and Bi₂S₃. The room temperature dark electrical resistivity for composite thin films is found to be of the order of 10⁴Ω-cm with n-type electrical conductivity was confirmed from thermoemf studies.