Photoconductivity of Lead Sulfide Films

The dark conductivity as a function of temperature, the photoconductivity as a function of temperature and irradiance, and the spectral response of chemically deposited PbS films have been investigated under dc conditions. The measurements indicate that a barrier model with a photoinduced change in carrier concentration accounts for the photoconductivity of the films, but that a model in which the barrier height is modified by illumination does not. A proposed physical model, based on the method of preparation of the films, predicts a change in the Fermi levels for holes and electrons on illumination to explain the experimentally determined dependence of photoconductivity on irradiance and temperature. The variation of photoconductivity and the equality of dark and light Hall mobility at dc and microwave frequencies found by Snowden and Portis can also be interpreted in terms of the model.