Density functional modelling studies of the single vacancy in large Ge clusters were made. A careful assessment was made of the origin of Jahn–Teller instabilities as a function of the vacancy net charge; resulting in various structural relaxations. By comparing the electron affinities of the vacancy with those of defects with well-established gap states, it was possible to estimate three acceptor states for the vacancy as being: E(-/0) = Ev+0.2eV, E(=/-) = Ec-0.5eV and E(≡/=) = Ec-0.3eV. As opposed to the Si vacancy, the defect in Ge was not a donor. It was also shown that these dissimilarities had fundamental implications for the electronic/atomic nature of other centres; such as transition metals in Ge crystals.

Electronic Structure and Jahn–Teller Instabilities in a Single Vacancy in Ge. J.Coutinho, R.Jones, V.J.B.Torres, M.Barroso, S.Öberg, P.R.Briddon: Journal of Physics - Condensed Matter, 2005, 17, L521-7