Trivacancy and trivacancy-oxygen complexes in silicon: Experiments and ab initio modeling

A center from the family of fourfold coordinated (FFC) defects, previously predicted theoretically, has been experimentally identified in crystalline silicon. It is shown that the trivacancy (V-3) in Si is a bistable center in the neutral charge state, with a FFC configuration lower in energy than the (110) planar one. V-3 in the planar configuration gives rise to two acceptor levels at 0.36 and 0.46 eV below the conduction band edge (E-c) in the gap, while in the FFC configuration it has trigonal symmetry and an acceptor level at E-c-0.075 eV. From annealing experiments in oxygen-rich samples, we also conclude that O atoms are efficient traps for mobile V-3 centers. Their interaction results in the formation of V3O complexes with the first and second acceptor levels at E-c-0.46 eV and E-c-0.34 eV. The overall picture, including structural details, relative stability, and electrical levels, is accompanied and supported by ab initio modeling studies.