Optical and electrical characterization of chemical bath deposited Cd–Pb–S thin films

Abstract

CdzPbyS thin films have been deposited on glass substrates using inexpensive chemical bath deposition technique. The aqueous solution containing precursors of Cd2+ and Pb2+ has been used to obtain good quality deposits at optimized preparative parameters. The thin film samples have been characterized through optical absorption, electrical conductivity and thermoelectric power measurement techniques. From optical studies, the absorption coefficient ‘α,’ is found to be of the order of 104cm−1. The optical absorption studies revealed direct band to band transition. The band gap energy is found to vary nonlinearly from 2.47eV (CdS) to 0.49eV (PbS) as the composition parameter ‘x’ was increased from 0 to 1. The electrical characterization revealed increased conductivity (σ) with the increased composition parameter up to x=0.175. The electrical conductivity measurements indicate two types of conduction mechanism, namely grain boundary scattering limited and variable range hopping conductions. The activation energies of the films of different compositions were determined at low and high temperature regions. The activation energies were observed to be in the range of 0.168–0.240eV and 0.514–0.711eV respectively. Thermoelectric power measurements highlighted n-type behavior of the as-grown thin film samples.