Early stage donor-vacancy clusters in germanium

There is considerable experimental evidence that vacancies in Ge dominate several solid state reactions that range from self-diffusivity to metal and dopant transport. It is therefore vital that we fully understand how vacancies interact with other point defects in Ge. Here we have a look at the properties of small donor-vacancy (Sb(n) V(m) with m,n <= 2) complexes in Ge by ab-initio density functional modeling. Particular attention has been payed to binding energies and to the electronic activity of the complexes. We found that all aggregates may contribute to the n -> p type conversion that is typically observed under prolonged MeV irradiation conditions. In general, Sb(n) V (m) defects are double acceptors. It is also suggested that spontaneous formation of Sb(3)V complexes may limit the activation level of donors introduced by ion implantation.