Diffusion instability of homogeneous distribution of mercury in cadmium mercury telluride

A mechanism of formation of inhomogeneities in the alloy Cd_xHg_1-xTe during either post-growth cooling or low-temperature annealing is proposed, based on a diffusion instability in the interacting system which includes cations in lattice sites, mercury interstitials and cation vacancies. The principal points of the mechanism are: (i) vacancies follow local variations of alloy composition, being always in local equilibrium; (ii) their concentration depends superlinearly on local composition. The uniform distribution of composition and the native dopants becomes unstable under a condition that is likely to be satisfied at temperatures below 200 °C in samples enriched with mercury interstitials. We show that the instability should result in the formation of a 'layered' doping profile where the concentration of mercury interstitials 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 electrophysical properties of the alloy are discussed.