Band gap engineering in PbS nanostructured thin films from near-infrared down to visible range by in situ Cd-doping

In this paper, we report on the modification of optical band gap of PbS nanostructured films over a wide spectral range (∼475-1000 nm) due to in situ Cd-doping and size confinement. The films investigated in this study are grown by chemical bath deposition (CBD) at different temperatures and the doping was conducted for a fixed impurity concentration. The PbS films grown under optimal deposition conditions are found to crystallize in face centered cubic (fcc) structure with an average crystallite size in the range of 22-27 nm. The estimated optical band gap was in the range of 1.22-1.42 eV, for films grown at different temperatures. Doping was found to influence the film growth and results in a reduction of crystallite size (down to 9 nm). Consequently, quantum size effect becomes pronounced in the Cd-doped PbS films, which lead to a significant enhancement in the optical band gap (up to 2.61 eV). X-ray photoelectron spectroscopy analysis confirms the substitutional doping of Cd into PbS lattice. Band gap modification due to quantum confinement and formation of ternary PbCdS are addressed.