We have calculated the lowest-energy configurations, stability, and electronic structures of vacancy aggregates (Vn) containing up to n=7 vacancies. The calculations were done using first-principles tight-binding molecular-dynamics simulations (in periodic supercells) and at (and near) the ab-initio Hartree-Fock level (in molecular clusters). The results show that the reaction Vn-1+ V1 → Vn is exothermic at least up to n=7. The most stable aggregate, by far, is the ring-hexavacancy (V6) which has remarkable properties. In contrast to the other Vn's, it is not vacancy-like: It has no deep level in the gap and its dipole moment is extremely small. It is sufficiently stable to survive high-temperature annealing. V6 is a small trigonal void which is likely to be a gettering center and is a plausible nucleus for a range of extended defects.
|Number of pages||6|
|Journal||Materials Science Forum|
|Issue number||PART 1|
|State||Published - 1997|