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 (Q_f) 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 Q_f. For example, on p-type MCT, with carrier concentration (N_A) of up to 5*10¹⁶ cm^-3, the passivant with Q_f 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.