Trivacancy and trivacancy-oxygen complexes in silicon: Experiments andab initiomodeling

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 ${E}_{c}\ensuremath{-}0.075\text{ }\text{eV}$. 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 ${V}_{3}\text{O}$ complexes with the first and second acceptor levels at ${E}_{c}\ensuremath{-}0.46\text{ }\text{eV}$ and ${E}_{c}\ensuremath{-}0.34\text{ }\text{eV}$. The overall picture, including structural details, relative stability, and electrical levels, is accompanied and supported by ab initio modeling studies.