Effect of dislocations on performance of LWIR HgCdTe photodiodes

The epitaxial growth of HgCdTe on alternative substrates has emerged as an enabling technology for the fabrication of large-area infrared (IR) focal plane arrays (FPAs). One key technical issue is high dislocation densities in HgCdTe epilayers grown on alternative substrates. This is particularly important with regards to the growth of HgCdTe on heteroepitaxial Si-based substrates, which have a higher dislocation density than the bulk CdZnTe substrates typically used for epitaxial HgCdTe material growth. In the paper a simple model of dislocations as cylindrical regions confined by surfaces with definite surface recombination is proposed. Both radius of dislocations and its surface recombination velocity are determined by comparison of theoretical predictions with carrier lifetime experimental data described by other authors. It is observed that the carrier lifetime depends strongly on recombination velocity; whereas the dependence of the carrier lifetime on dislocation core radius is weaker. The minority carrier lifetime is approximately inversely proportional to the dislocation density for densities higher than 105 cm−2. Below this value, the minority carrier lifetime does not change with dislocation density. The influence of dislocation density on the R0A product of long wavelength infrared (LWIR) HgCdTe photodiodes is also discussed. It is also shown that parameters of dislocations have a strong effect on the R0A product at temperature around 77 K in the range of dislocation density above 106 cm−2. The quantum efficiency is not a strong function of dislocation density.