Analysis of surface leakage currents due to Zener tunnelling in HgCdTe photovoltaic diodes

A model is presented to calculate the surface leakage currents due to Zener tunnelling in n+-p mercury cadmium telluride (MCT) photovoltaic (PV) diodes. The expressions describing the effect of fixed interface charge density (Qf) on zero-bias resistance-area product (R0A) are developed for situations where the interface charges due to passivant accumulate the MCT surface. Calculations for detectors with 9.55, 10.60 and 11.55 mu m cut-off wavelengths operating at liquid-nitrogen temperature show that I-V characteristics, and thus R0A products, of these diodes have a strong dependence on Qf. For example, on p-type MCT, with carrier concentration (NA) of up to 5*1016 cm-3, the passivant with Qf of greater than 3.2*1010 cm-2 would degrade the performance of these detectors significantly. The experimental results agree reasonably well up to moderate fields (i.e. up to 400-500 mV of reverse bias) with the predictions of this model.