A complete microscopic picture of the Ge vacancy was derived, and compared with measurements. First-principles calculations were used to analyze structural relaxations, Jahn-Teller distortions and orbitals for the charge states (++, +, 0, -, --). The formation energies of the various charge states were predicted; as well as the positions of the (++/+), (+/0), (0/-) and (-/--) levels. It was deduced that the vacancy was not an Anderson negative-U system, unlike the Si vacancy. This was suggested to explain the much smaller electron-lattice coupling for the E mode in Ge, as compared with Si.

Microscopic Picture of the Single Vacancy in Germanium A.Fazzio, A.Janotti, A.J.R.Da Silva, R.Mota: Physical Review B, 2000, 61[4], R2401-4