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 p lane arrays (FPAs). One key technical issue is high dislocation densities i n HgCdTe epilayers grown on alternative substrates. This is particularly im portant with regards to the growth of HgCdTe on heteroepitaxial Si-based su bstrates, which have a higher dislocation density than the bulk CdZnTe subs trates typically used for epitaxial HgCdTe material growth. In the paper a simple model of dislocations as cylindrical regions confined by surfaces wi th definite surface recombination is proposed. Both radius of dislocations and its surface recombination velocity are determined by comparison of theo retical predictions with carrier lifetime experimental data described by ot her authors. It is observed that the carrier lifetime depends strongly on r ecombination velocity; whereas the dependence of the carrier lifetime on di slocation core radius is weaker. The minority carrier lifetime is approxima tely inversely proportional to the dislocation density for densities higher than 10(5) cm(-2). Below this value, the minority carrier lifetime does no t change with dislocation density. The influence of dislocation density on the R(o)A product of long wavelength infrared (LWIR) HgCdTe photodiodes is also discussed. It is also shown that parameters of dislocations have a str ong effect on the R(o)A product at temperature around 77 K in the range of dislocation density above 10(6) cm(-2). The quantum efficiency is not a str ong function of dislocation density.