It was recalled that there had been recent reports of the electron paramagnetic resonance identification of the atomic and electronic structures of the Te and Cd vacancies. The resolved hyperfine interactions with the nearest Cd or Te neighbors furnished a conclusive identification of the defects. By means of photo-electron paramagnetic resonance investigations, threshold energies were obtained for re-charging of the respective defects. In the case of VTe, its electron ionization transition from the neutral to the positive charge state began at 1.4eV and thus caused the energetic level to be situated at Evb + 0.2eV. It acted as a single donor. The Cd vacancy acted as a double acceptor. In the absence of illumination, VCd was found in its singly negative charge state in samples which had been annealed under a Te over-pressure. Due to the presence of a Jahn-Teller distortion, it was possible to put only an upper limit on its (--/-) level, at lower than Evb + 0.47eV. Neither vacancy was a very common defect in as-grown or donor-doped material. The Te vacancy was observed, only after annealing under vacuum conditions, in concentrations which were well below 1016/cm3. At 400C, the VCd concentration was about 1017/cm3, but was lower (about 5 x 1015/cm3) at room temperature. Cation vacancies were not observed after 2MeV electron irradiation. The low VCd content in as-grown material was attributed to the fact that residual impurities (Cu, Ag) predominantly occupied the Cd sub-lattice. Both were single effective mass-like acceptors and, depending upon the growth method, could be present in concentrations of up to 1017/cm3. Undoped (Cd,Zn)Te and Cl-doped CdTe could be grown so as to have resistivities which were much greater than 1019/cm3. This required the presence of a compensating deep center which was close to the mid-gap. It was suggested that, in material which was grown from Te-rich melts, the anion antisite (TeCd) could be the required center.

B.K.Meyer, P.Omling, P.Emanuelsson: Materials Science Forum, 1994, 143-147, 397-8