Effects of blocking contacts on generation-recombination noise and responsivity in intrinsic photoconductors

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Abstract
A theory is presented of generation‐recombination (g‐r) noise, responsivity, and detectivity D* in intrinsic photoconductors, including for the first time the effects of recombination at the contacts as a variable parameter. The contacts are described using a contact recombination velocity. Increasing the blocking at the contacts can significantly increase the responsivity, and also push the detectivity toward the background limited value since blocking contacts increase responsivity and the background contribution to the noise voltage faster than the thermal contribution. Blocking contacts also cause both the responsivity and g‐r noise voltage to roll off at lower frequencies. Numerical calculations are presented for X∼0.2 HgCdTe photoconductors. Blocking contacts are found to increase the range of material parameters which can be used to make detectors. For example, under typical conditions, to reach responsivities of 105 V/W and detectivities of 6×1010 cm(Hz)1/2/W at T=77 °K, blocking contacts can increase the maximum allowed carrier density from about 4×1014 to about 2×1015 cm−3, and enlarge the required composition window from about 0.200<xx<0.212 for typical device geometries.