Modification of electrical, optical and crystalline properties of chemically deposited CdS films by thermal diffusion of indium and tin

In a recent work we reported that chemically deposited intrinsic CdS thin films can be converted into n-type with an electrical conductivity of similar to 102 Omega(-1) cm(-1) by solid state diffusion of indium at temperatures of 300-350 degrees C from a thin film of indium deposited by thermal evaporation on the CdS surface. In the present study, we report on the enhancement of grain size accompanying this diffusion process and its correlation with a reduction in the optical bandgap. X-ray powder diffraction patterns show that the typical grain size, similar to 13 nm, of the as-deposited CdS film of 150 nm thickness increases to about 17 nm when the CdS-ln film is heat treated at 350 degrees C for 1 h. There is a corresponding decrease in the optical bandgap from 2.58 eV (as-prepared) to 2.37 eV (heat treated CdS-ln). The heat treatments of CdS only and CdS-Sn films have also led to an increase in the electrical conductivity by a factor of 10(8) and a reduction in the bandgap, but with little effect on grain size.