Thermodynamic description of metal Hg(Cd)Te systems

Abstract

The interactions of Hg(Cd)Te with metals used as potential contacts have been shown to be quite complex, both in terms of electrical as well as metallurgical properties. In an attempt to model such behavior the use of a concept of a metals ‘‘reactivity’’ toward Hg(Cd)Te has been suggested. In this article we investigate the ternary or quaternary phase diagrams of metal Hg(Cd)Te systems and show that a much better understanding of these systems is possible using such diagrams rather than the somewhat ambiguous concept of reactivity. For most metals three basic types of ternary diagrams describe the M–Hg–Te system. In principal, all metals for which there is not a metal–HgTe tie line would be considered reactive. Indeed, the only common metal for which there is a M–HgTe tie line is Au. However, even in this case, Au deposition onto a room temperature free surface may lead to Hg evaporation due to the extra RT ln PHg term in ΔG unless there is a sufficient Hg overpressure. Low deposition temperatures can be used to mitigate this effect, however. The ‘‘reactive’’ systems fall into two categories, one where the elemental Hg/metal telluride couple is stable and one for which the Hg metal compound/metal telluride couple is stable. Al, In, Cd, Ti, and possibly Cu and Ge, fall into the former category whereas Pt, Pd, and possibly Ag, fall into the latter.