Epitaxial Lead Sulfide Photovoltaic Cells and Photoconductive Films

Single-crystal lead sulfide photovoltaic cells and photoconductive films were prepared using epitaxial growth techniques. The spectral response of the photovoltaic cells is characterized by a sharp peak at wavelengths just short of the energy gap of PbS. The photoconductive films were grown with carrier concentrations as low as 3×1016 cm−3 and exhibit two large, distinct photoconductive signals when cooled to 77 °K. One response is characterized by a time constant > 50 msec and is attributed to photoexcitation of electrons from oxygen-induced surface traps. The second response has a time constant of 32 μ sec and is attributed to intrinsic photoconductivity of lead sulfide.