EFFECT OF DOPING CONCENTRATION ON THE OPTICAL PROPERTIES OF NANOCRYSTALLINE Zn DOPED PbS THIN FILMS DEPOSITED BY CBD METHOD

Nanocrystalline PbS and Zn doped PbS thin films have been deposited on glass substrates by chemical bath deposition (CBD) method. The as deposited thin films were found to be crystalline having cubic phase structure. The optical properties of the undoped and Zn doped PbS thin film have been studied. The chemically prepared Zn doped and undoped nanocrystalline PbS films have high absorbance in the UV-visible region. The linear nature of (αhν)2 vs (hν) plots of PbS thin films confirmed that the transition is direct and the optical band gap energy of PbS films is found to increase from 1.90 eV to 2.28 eV with decreasing crystallite size from 29 nm to 15 nm and these obtained band gap values are higher than the bulk value (0.40 eV). The increase in optical band gap supports the quantum confinement effect in the PbS thin films prepared by CBD technique. The optical band gap of Zn doped PbS films are found to increase with increase in dopant concentrations.