Optoelectronic and thermoelectric properties in Ga doped β- PbS2 nanostructured thin films

Lead sulphide nanostructured thin films were grown on soda lime glass substrates by chemical bath deposition. The films were then doped with gallium using vacuum evaporation technique. X-ray diffraction (XRD) established the structural type of the host films to be tetragonal β-PbS2 with average grain size of the order of 15 nm. The nanostructure of films was further confirmed from scanning electron and atomic force micrographs. The shift in the binding energies of the 4f and 4d states of lead, 2p state of sulphur and the 2p states of Ga from their elemental binding energy values, determined from X-ray photoelectron spectroscopy (XPS), indicated intact chemical bonding in the compound. Compositional analysis showed about 0.01% doping of Ga into PbS2. Low temperature thermopower measurements indicated p-type conductivity for the films with Fermi level positioned at about 0.017 eV above the maxima of valence band. Optical absorption studies in conjunction with photo sensitivity measurements established its pertinence in junction formation in photovoltaic applications due to the blue shift in the band gap to 2.37 eV and the increased photoconductivity of the films.