Properties of PbS thin films grown on glass and layered GaSe crystal substrates by chemical bath deposition

PbS thin films were grown on glass and GaSe crystal substrates by chemical bath deposition and their structural, morphological, optical, and electrical properties were investigated. PbS films grew in cubic structure with lattice constants equal to 5.9315 angstrom and 5.9362 angstrom for films grown on glass and GaSe crystal, respectively. The band gaps of the PbS films were determined to be 1.60 eV. The long wavelength tails of absorption spectra showed exponential dependence on the incident photon energy according to the Urbach-Martiensen model. Electrical properties of PbS films were investigated by the van der Pauw method, which showed that PbS films were p and n type depending on the temperature. At low temperatures, the p-type conductivities of PbS thin films grown on glass and GaSe substrates were found to be due to the ionization of acceptor centers with energies of 94.50 meV and 36.50 meV, respectively, while at higher temperatures the n-type conductivities were found to be determined by the ionization of donor centers with energies of 226.50 meV and 310 meV, respectively. The sheet charge carrier concentration and mobility of PbS film grown on GaSe substrate were, in general, higher than those of films grown on glass substrate.