Improved model for surface shunt resistance due to passivant for HgCdTe photoconductive detectors

We present the results of calculations for surface shunt resistance due to the passivant fixed charge density (Qss) in n-HgCdTe photoconductive (PC) detectors. To the best of our knowledge, this is the first detailed calculation involving the actual majority carrier profile at the accumulated surface. The effect of surface field (or potential) due to heavily accumulated density of majority carriers on surface mobility (μs) has been investigated in detail by employing the Schrieffer and Goldstein models using random diffuse scattering. Additionally, the effect of lateral field (applied to these devices) on surface mobility is included by invoking the model of Yoo et al. The above effects were not taken into account in previous simplified models. For narrow-band, n-type HgCdTe the effects of carrier degeneracy and band non-parabolicity cannot be neglected. In this work, a one-dimensional model including these effects has been developed to evaluate the detector resistance and responsivity. A proper two-layer (bulk and surface) responsivity model is developed. The results are compared with the widely-used approximate one-layer model of Reine and with the step model proposed by Bhan and Gopal. It is shown that, for the Reine model, the agreement with the present model depends on the value of μs chosen. The trend of the step model agrees with the Reine model, but both models show disagreement with the present one-layer and two-layer profile models for Qss ≈ (1010–1012) cm−2.