Characterization of chemical bath deposited CdS thin films doped with methylene blue and Er3+

The optical, electrical, and structural properties of CdS thin films grown by chemical bath deposition and simultaneously doped with methylene blue (MB) and Er³⁺ were studied. Doping was achieved by adding a constant volume of an MB aqueous solution to the chemical bath while the relative volume (V_R) of the Er aqueous solution varied within the range 0–10% of the total growing solution. X-ray diffractograms displayed the zincblende crystalline structure for all the CdS samples, with a remarked preferred orientation along the (111) direction. The interplanar distance among the (111) planes decreased for low doping leves of Er³⁺, while for high doping concentrations such distance increased to saturation. Measurements on the carriers density indicated that the CdS thin films doped with Er³⁺ at 6% V_R presented the maximum value. In addition, the band gap energy (Eg) resulted higher for CdS:MB films with low Er³⁺ doping levels than for undoped films; however, Eg decreased until stabilization for increasing Er³⁺ concentrations.