Effect of built-in electric field on crosstalk in focal plane arrays using HgCdTe epilayers

Abstract

A simple two-dimensional model, for calculating the effect of the built-in electric field arising in HgCdTe epilayers due to the composition gradient that occurs in LPE growth, on the crosstalk is developed for the case of a back illuminated focal plane array. The calculations predict that the crosstalk does not decrease monotonically with increasing electric field (i.e., weak peaks occur), unlike in the simple one-dimensional model of Kamins and Fong. The zero-field crosstalk varies between 1% and 10%, depending upon the material parameters. For electric fields in the range of 1–10 V cm −1, the crosstalk is reduced to negligible values (<0.01%). The model is approximate to the extent that the effect of the electric field in reducing the crosstalk is somewhat overestimated. The crosstalk depends strongly on the diffusion length and on the absorption coefficient, but very weakly on the diffusion velocity of carriers. The effects of diode size and dead space are similar to those of other models. The effect of the CdTe–HgCdTe interface recombination velocity has been taken into account, whereas that of the top surface recombination velocity has been neglected. The crosstalk to the second nearest neighbour diode is an order of magnitude smaller than that to the first neighbour diode. It goes to zero at a much smaller electric field. The crosstalk is shown to be slightly higher in medium wavelength IR arrays (MWIR) than in long-wavelength IR (LWIR) arrays.