Perturbed-angular-correlation Studies of In-vacancy Pairs in Hg1−xCdxTe

The interaction of vacancies with In111 atoms is studied in Hg1−xCdxTe compounds via perturbed-angular correlation (PAC) experiments, for x=0.065, 0.21, 0.44, and 0.95. In the low-x (Hg-rich) compounds, Hg vacancies are created by heating in vacuum. For the x=0.21 alloy, we have previously shown that InC-vacC pairs (A centers consisting of an In atom on a cation site and a vacancy at a neighboring cation site) are abundant after quenching from elevated temperatures. These defects are characterized by two PAC signals with quadrupole interaction frequencies νQ1=83 MHz and νQ2=92 MHz, and asymmetry parameters η1=η2=0.08. For the x=0.065–0.44 alloys, the data presented in this article show that the fractions f1 and f2 of In atoms associated with these two frequencies vary with x according to whether one or two Hg atoms are nearest neighbors to the Te atom that is bound to the In atom and the vacancy. The data are explained by the polarizable point-ion model. For the x=0.95 compound, PAC signals are observed only when stable In is added to the compound, indicating that the presence of In creates vacancies, and that self-compensation via A centers is dominant. In this case, the well-known frequencies νQ4=100 MHz and νQ5=112 MHz are seen for samples quenched from several different temperatures between 325 and 525 °C, or slow cooled from 475 °C or below. In contrast, for a sample slowly cooled from 525 °C, the frequency νQ6=60 MHz was dominant. This signal could be due to InC−vacC pairs in which the vacancy is singly charged, or to In-group I pairs. We attribute the frequencies νQ4=100 MHz and νQ5=112 MHz, like νQ1 and νQ2, to InC-vacC pairs having doubly charged vacancies.