Influence of Crystal Size on the Spectral Response Limit of Evaporated PbTe and PbSe Photoconductive Cells

Photoconductive layers of have been formed by evaporation on substrates at different temperatures. The size of crystals in the layers has been estimated from electron micrographs and x‐ray diffraction, and a correspondence has been obtained between crystal size and the limit of spectral response. Sensitivity up to the long wave‐length limit set by the energy gap is not achieved unless the crystals are greater than a critical size; for lead telluride this is about a quarter of a micron. A similar effect has been shown to occur with .