Indirect photon interaction in PbS photodetectors

A sensitization process by heat treatment in oxygen atmosphere was used in order to increase the photoconductivity of vacuum evaporated PbS thin films. The Fourier analysis of the (200) PbS X-ray diffraction profile has shown a decrease of the crystallites mean size and an increase of the sensitized PbS lattice distortion because of chemisorption of oxygen at the crystallites surfaces. The crystallites mean size distribution function indicates that the sensitized PbS film is a heterogeneous system of 320 Å size crystallites separated by 160 Å intercrystalline barriers. The optical photoacoustic spectra of the sensitized PbS film shows an absorption structure at low photon energies of the 0.47 eV absorption threshold. The broadening effect observed in the absorption spectrum suggests an indirect photon transitions in the fundamental absorption region.