The electronic and geometrical structure of impurity-vacancy complexes in Si and Ge were examined. It had already been suggested that, in Si, the pairing of Sn with the vacancy produced a complex with the Sn-atom at the bond center and the vacancy split into 2 half-vacancies on the neighboring sites. Within the framework of density-functional theory, 2 complementary ab initio methods were used: the pseudopotential plane-wave method and the all-electron Kohn-Korringa-Rostoker method, to investigate the structure of vacancy complexes with 11 different sp-impurities. For the case of Sn in Si, the split configuration was confirmed and good agreement with the electron paramagnetic resonance data of Watkins was obtained. In general it was found that all impurities of the 5sp and 6sp series in Si and Ge prefer the split-vacancy configuration, with an energy gain of 0.5–1eV compared to the substitutional complex. On the other hand, impurities of the 3sp and 4sp series form a (slightly distorted) substitutional complex. Al impurities showed an exception from this rule, forming a split complex in Si and a strongly distorted substitutional complex in Ge. A strong correlation of these data with the size of the isolated impurities was found, being defined via the lattice relaxations of the nearest neighbors.

Vacancy Complexes with Oversized Impurities in Si and Ge. H.Höhler, N.Atodiresei, K.Schroeder, R.Zeller, P.H.Dederichs: Physical Review B, 2005, 71[3], 035212 (7pp)