Experimental evidence for the third level (А+) of Hg vacancy in Hg1−xCdxTe

Mercury vacancy in Hg1-xCdxTe is not a two-level (as it was supposed until now), but a three-level acceptor. A third, most shallow (1–1.5 meV) level (А+ state) appears due to a capture of a third hole by a neutral acceptor, after the two deeper vacancy levels (A− and А0 states) are already occupied by holes. Due to a capture of nonequilibrium holes by neutral mercury vacancies (under radiation) a positive space charge region arises near an irradiated surface. This causes the anomalies of photoelectromagnetic effect, observed in р-Hg1−xCdxTe at T < 10–12 K.