Theory of generation-recombination noise and responsitivity in overlap structure photoconductors

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Abstract
A rigorous theory of both responsitivity and generation‐recombination noise in overlap structure photoconductors is presented. Because generation‐recombination noise dominates under typical operating conditions, these results combine to give the detectivity D*. It is found that both responsivity and D* can be improved by use of the overlap structure. The dependence of the optimum device geometry on the operating conditions, such as bias conditions, and on the parameter to be maximized (e.g., responsivity or D*), is derived. Symmetric and asymmetric overlap structure are compared, and it is found that, except at very small bias fields, an asymmetric structure gives the largest improvement in both the responsivity and D*. Both responsivity and noise voltage are found to roll off at lower frequencies for the overlap structure than for the standard design, but become equal to the standard design values at high frequencies. Numerical results for x≊0.21 HgCdTe detectors are presented. Using an asymmetrical overlap structure the theory predicts that, under usual operating conditions, the responsivity can be more than doubled and simultaneously D* increased by over 15%. Under optimum conditions D* for the overlap structure photoconductor can equal the usually quote value of D*BLIP for a photovoltaic device; that is, it can exceed the usually quoted value of D*BLIP for a photoconductor by as much as a factor of .