Effect of selenium doping on the deposition and properties of cadmium sulfide thin films grown by a chemical bath deposition technique

Abstract

The present study highlights the changes in various physical properties of cadmium sulfide (CdS) thin films induced by doping with the chalcogenide ion Se. The films were obtained by a chemical bath deposition technique at low temperature, good quality thin films were synthesized, with the advantage of doping in-synthesis without the need for additional step. The structural analysis was carried out using grazing incidence X-ray diffraction, revealing that the incorporation of selenium led to the formation of two crystalline phases of CdS and CdSe, and a decrease in their crystallite size. The transmittance spectrum shows that the added selenium shifts the transmission region to higher wavelengths and reduces the transmittance. The films composition was determined by wavelength-dispersive X-ray fluorescence, revealing a lower fraction of selenium in the films than in the bath solution. By the oscillations in transmittance the film thicknesses were estimated, and it was found that they are reduced by the incorporation of selenium, this is in accordance with the decrease of the intensity of the X-ray diffraction and X-ray fluorescence peaks. The photoluminescence study shows that the higher energy emissions (close to 2.0 and 2.2 eV) are reduced and eliminated with the incorporation of Se into the material. This is attributed to shallow electron traps induced by the metal ion selenium. The characterization of the films indicates that incorporating selenourea into the chemical bath, using the specified working conditions, modifies the film deposition process and results in a red-shift of the absorption region.