Some properties of a double acceptor center in CdTe

Abstract

When CdTe and other II-VI semiconducting compounds are heat treated with an excess of the cation component or are subjected to high-energy electron bombardment, a double acceptor is produced that has its second charged state close to the conduction band. The defect is characterized by its unique properties manifested in electrical transport and photoconductivity measurements. This paper deals with this imperfection in CdTe. It is shown that all of the observed properties associated with the defect are consistent with the double acceptor model. The energy of the doubly ionized state is 0.06 eV below the conduction band minimum. In this state the defect is an effective hole trap at low temperatures. Electrons are strongly inhibited from recombining at the singly ionized center by an effective "barrier" of 0.27 eV. At moderately low temperatures (T85°K), this phenomenon leads to marked departures from electronic equilibrium. On the basis of the preparative conditions leading to the center's production, it is suggested that the imperfection involves a native defect, most probably a vacancy, associated with a chemical impurity. Another defect with a level 0.6 eV below the conduction band, reported earlier by deNobel in heavily doped material, is found to be produced in samples fired under moderately low cadmium pressure. From the firing conditions and the Hall data it is inferred that this level is also due to an intrinsic imperfection. © 1964 The American Physical Society.