DIFFUSION INSTABILITY OF HOMOGENEOUS DISTRIBUTION OF MERCURY IN CADMIUM MERCURY TELLURIDE

A mechanism of formation of inhomogeneities in the alloy CdxHg1-xTe du ring either post-growth cooling or low-temperature annealing is propos ed, based on a diffusion instability in the interacting system which i ncludes cations in lattice sites, mercury interstitials and cation vac anies. The principal points of the mechanism are: (i) vacancies follow local variations of alloy composition, being always in local equilibr ium; (ii) their concentration depends superlinearly on local compositi on. The uniform distribution of composition and the native dopants bec omes unstable under a condition that is likely to be satisfied at temp eratures below 200-degrees-C in samples enriched with mercury intersti tials. We show that the instability should result in the formation of a 'layered' doping profile where the concentration of mercury intersti tials varies by a factor of 2-3 while the variation of composition is of the order of 10%. Possible consequences of this effect for the elec trophysical properties of the alloy are discussed.