It was recalled that the cation vacancy in this material was commonly used for p-type doping. However, the energy levels of the vacancy acceptor were not known. It was suggested that the vacancy was a negative-U center, with inverted energy levels. A comparison with a similar vacancy in Si indicated that the (Cd,Hg)Te vacancy was also likely to be of negative-U type. A minority carrier recombination rate which involved gap levels of the vacancy was expected to exhibit a quadratic dependence upon the vacancy concentration. It was proposed that the deep levels of a negative-U vacancy would be particularly suitable as recombination centers, due to their location near to the middle of the gap.

D.E.Cooper, W.A.Harrison: Journal of Vacuum Science and Technology A, 1990, 8[2], 1112-5