Photoconductive extrinsic semiconductors, the photon energy is

Photoconductive detectors mechanism produce the conductance change of PV when IR is incident on it. In PC detectors, the free charge carriers produced by the light energy cause increase of the conductance of photoconductive material under the influence of applied constant electric field.

The detector material can be either an intrinsic or an extrinsic semiconductor. The spectral response of a semiconductor material can be controlled by the doping of the intrinsic semiconductor to make PC detectors applicable in LWIR detection. In the case of intrinsic semiconductor, the incident IR radiation is absorbed by semiconductor to generate holes and electrons. In the case of extrinsic semiconductors, the photon energy is absorbed by the impurity, and only the majority carriers are excited. Under the applied constant bias, the resultant current level is proportional to the incident photon flux. In PC detectors, the photoconductive gain is defined as the ratio of carrier lifetime to detector transit time.

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The gain usually varies from 0.5 to greater than unity. If carrier lifetime is longer than transit time, the free carriers can transit across the detector without recombination and the current gain is greater than one. Since the current flows under a constant electric field, thephotoconductive detector consumes power and generates heat. This makes it unsuitable for large IR