Characterization of chemically-deposited aluminum-doped CdS thin films with post-deposition thermal annealing

Aluminium-doped CdS thin films were grown, using chemical bath deposition, on glass substrates in an ammonia-free system, with post-deposition thermal annealing at 300 ° C in air atmosphere. Their structural, morphological, mechanical, electrical and optical properties were studied by X-ray diffraction (XRD), atomic force microscope (AFM), nanoindentation, four-point probes method and UV-Vis spectrophotometer, respectively. XRD patterns show that doped CdS films have an hexagonal structure, with preferred orientation along the (0 0 2) plane, and their average crystallite size start to decrease when Al content reaches a certain value. The AFM studies reveal that surface roughness decreases with thermal annealing. Additionally, we found that the Young's modulus and hardness of the films decreases with increasing Al doping, and the electrical resistivity decreases with thermal annealing. The band gap was found to be in the range of 2.39-2.49 eV for as-deposited films and 2.33-2.39 eV for annealed films. Current-voltage (I-V) measurements were also carried out to the films, which showed rectifying behavior with Ag contacts for some doping levels.