Field-effect modulation of detectivity in PbS photoconductors

Abstract
Results obtained with lead sulfide photoconductive insulated‐gate field‐effect transistors (photo‐IGFET’s) are presented. Detectivity modulation is provided by the gate electrode. The n‐type PbS film was depleted of carriers by applying a negative gate potential, and the detectivity was increased by a factor of 200 while the noise remained constant. Detectivities of 2×1010 cm Hz1/2/W were obtained at 173 °K and 500 Hz for a 180° field of view and a 300 °K background. The devices exhibited stable operating characteristics and showed no significant performance change after 18 months under ambient laboratory conditions. They were fabricated entirely by vacuum deposition in a single pumpdown, and the various conducting, insulating, and semiconducting films were deposited successively through accurately registered metal shadow masks.

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