Enhanced diffusion and interdiffusion in HgCdTe from Fermi-level effects

Excessive dopant or compositional mixing (interdiffusion) during the proces sing of HgCdTe photodiodes can lead to significant reductions in device per formance. With the advent of multi-color and wider bandgap detectors, proce sses developed for single color LWIR and MWIR devices may not be transferab le to the more complex structures. An important factor to account for in pr ocessing multicolor and wider gap HgCdTe is the effect of the Fermi level o n point defect (PD) concentrations. In general, the density of PDs that hav e donor states in the band gap will be boosted in the presence of accepters through the energy gained by the donor state electrons dropping into the v acant acceptor states. The density of PDs that have acceptor states in the band gap will be boosted in the presence of donors through a similar compen sation mechanism. This Fermi-level effect is increasingly more important as the band gap is widened. Since almost all diffusion is mediated by either native and/or dopant point defects, and the intrinsic carrier concentration is relatively low at typical processing temperatures, significant broadeni ng of composition and dopant profiles can occur in moderately and heavily d oped HgCdTe. In this paper, we illustrate the Fermi-level effect on diffusi on with two examples: compositional interdiffusion in multicolor detectors and diffusion of indium in MWIR and SWIR detectors.