Native Defect Formation and lonization Energies in Cadmium Telluride

摘要

Deep intrinsic energy levels near the middle of the band gap in CdTe have been reported in a number of experiments. Based on earlier defect-supercell electronic structure calculations, at least some of these features have been attributed to the second ionization level of the Cd vacancy, while the Te_(Cd) antisite, possibly complexed with a Cd vacancy, has also been suggested to account for some midgap levels. Using high-accuracy LDA calculations with full lattice relaxation out to third neighbors, we find that (ⅰ) both acceptor states of the Cd vacancy are shallow, (ⅱ) the donor states of an isolated Te_(Cd) are both more than 1 eV above the valence band maximum, (ⅲ) the Te_(Cd)-V_(Cd) complex does indeed have acceptor states near midgap in CdTe and probably accounts for the native defect states in that energy range.