Influence of film thickness and In-doping on physical properties of CdS thin films

• Fabrication of polycrystalline CdS thin films by Close Spaced Sublimation technique.
• The direct band gap of 2.44 eV and the electrical resistivity in the order of 106–108 Ω cm was measured.
• Resistivity was reduced to the order of 10–2–101 Ω m by the thermally diffusion of indium into CdS films.

Polycrystalline CdS thin films were deposited on glass substrates by close spaced sublimation technique. Samples of various thicknesses, ranging from 250 to 940 nm were obtained. The optical and electrical properties of pure CdS thin films were studied as a function of film thickness. The resistivity of as-deposited CdS films was in the order of 106–108 Ω cm, depending upon the film thickness. In the high temperature region, carriers are transported over the grain boundaries by thermionic emission. Resistivity was reduced to the order of 10−2–101 Ω cm by the thermally diffusion of indium into CdS films, without changing the type of carriers. The annealing temperature dependence of structural, optical and electrical properties of In-doped CdS films showed that the samples annealed at 350 °C and 400 °C exhibited better results.