TIGHT-BINDING STUDIES OF CRYSTAL STABILITY AND DEFECTS IN BI2TE3

The stability of the crystal structure and the electronic state of iso lated point defects have been studied in Bi2Te3. The structure is rela ted to p-bonding, giving a basic cubic cell further stabilized by the formation of units of five layers of planes along the [111] axis of th e cubic cell. The impurities are treated via the Lifshits-Koster-Slate r method- Antistructure defects appear as single donors (Te(Bi)) or si ngle acceptors (Bi(Te)). Vacancies are strong perturbations: V(Te) are double donors and V(Bi) are triple acceptors. The impurities of colum n IV when substituted for Te give a resonance (or bound state) close t o the gap. Their electrical activity may then vary from double accepto r to inactive.