Special features of hopping conduction in p-Hg0.78Cd0.22Te crystals under conditions of dual doping

Abstract

At T=4.2–125 K, the electrical conductivity and Hall effect were studied in p-Hg0.78Cd0.22Te crystals that contained 3×1016 cm−3 Cu atoms and 1.83×1016 cm−3 of Hg vacancies (either simultaneously or independently of each other). In such crystals, the ɛ1 conductivity over the valence band is dominant at temperatures above 10–12 K, whereas the hopping conduction is prevalent at temperatures below 8–10 K. In the samples containing copper atoms and mercury vacancies simultaneously, conductivity with variable-range hopping is observed. It is found that the ɛ1 conductivity of the copper-doped crystals is independent of the presence of mercury vacancies, whereas the hopping conductivity increases appreciably if these vacancies are introduced into the undoped crystal. This phenomenon is attributed to attachment of holes to the neutral mercury vacancies. The energy of this attachment is calculated, and it is found that this energy is equal to 3.7 meV for the ground state. The fluctuation-related broadening of the impurity band in the solid solutions gives rise to the overlap of the impurity bands formed by the copper acceptor levels and by the levels of holes attached to vacancies.