Some structral, electrical and optical properties of Cd1-xCoxS thin films prepared by chemical bath deposition technique

In this study, the effects of the doping cobalt on the CdS thin films, which are II-VI group semiconductor, have been investigated. Cd1-xCoxS (0  x  0,1) thin films were prepared on glass substrates by chemical bath deposition technique. The structural, electrical and optical properties of these thin films were investigated. The thickness of the thin films were about 152–130 nm. The crystal structure of prepared samples had the mixed phase. The grain size of the samples decreased from 200 nm to 100 nm with cobalt doping. Stoichiometry of the samples deteriorated with the doping concentration increases. Cobalt doping decreased the optical transmittance of the samples from 85% to 65%. Cd1-xCoxS thin films had two band gap, which are belong to cubic and hexagonal phase. The band gap of the hexagonal phase decreased from 2,97 eV to 2,88 eV as the band gap of the cubic phase increased from 2,37 eV to 2,41 eV with cobalt doping. The carrier concentration and the electron mobility of the samples decreased, and the resistivity of the samples increased with Co doping. Several thin films were annealed at 473, 573 and 673 K for 20 minutes in the vacuum of 210–2 torr. In the XRD patterns of the annealed samples were not appeared a new peak. The crystal structure of the annealed samples had the mixed phase. The grain size of Co doped samples for x = 0,075 and x = 0,1 ratios was not changed after the annealing. The grain size of the other samples increased with annealing. Stoichiometry of the annealed samples was improved. For all samples the band gap of the hexagonal phase increased as the band gap of the cubic phase decreased after the annealing. The carrier concentration and the electron mobility of the annealed samples decreased, and the resistivity of the annealed samples increased.