Contribution of dislocations to the zero-bias resistance-area product of LWIR HgCdTe photodiodes at low temperatures

Dislocations in the base material are shown to significantly influence zero-bias impedance of long wavelength infrared HgCdTe photodiodes by acting as a shunt, and by influencing their minority carrier lifetime. Consequently, temperature dependence of zero-bias resistance-area product (R₀A) of these photodiodes can be described very well over a broad temperature range, down to 25 K, after taking into account the temperature and dislocation dependence of the minority carrier lifetime in addition to the shunt resistance contribution of dislocations. Further, based on the theoretical prediction that the shunt resistance contribution of a dislocation is a sensitive function of the magnitude of the charge around its core, it is proposed that the scatter of the R₀A experimental data in diodes with dislocation densities of less than 1×10⁷ cm^-2 could be the result of statistical variations in the charge around the core of dislocations. Interaction of dislocations among themselves may be responsible for deviations above dislocation densities of 1×10⁷ cm^-2.