CdS thin films doped with metal-organic salts using chemical bath deposition

CdS thin films doped with metal-organic salts were grown on glass substrates at 90 °C by the chemical bath deposition technique. Metal-organic salts such as zinc acetate, chromium acetylacetonate, ammonium fluoride, aluminum nitrate, tin acetate and indium acetate were used. The chemical bath was prepared with cadmium acetate, ammonium acetate, thiourea and ammonium hydroxide. In the case of un-doped films, the S/Cd ratio was varied by changing the thiourea in the range 1–12. The best optical, structural and electrical properties were found for S/Cd = 2. The doped films were prepared by always keeping the ratio S/Cd constant at 2. The band gap (Eg) of doped and un-doped films was evaluated from transmittance spectra, where films with lower sulfur concentration exhibited higher Eg. X-ray analysis showed that both un-doped and doped films were polycrystalline with preferential orientation along the (111) direction and with the zincblende structure in all cases. The dark electrical results showed that CdS doped with Zn (1 at.%) exhibited the lowest resistivity values of 10 Ω cm.