Fluorine codoping in germanium to suppress donor diffusion and deactivation

Electronic structure calculations are used to investigate the stability of fluorine-vacancy (FnVm) clusters in germanium (Ge). Using mass action analysis, it is predicted that the FnVm clusters can remediate the concentration of free V considerably. Importantly, we find that F and P codoping leads to a reduction in the concentration of donor-vacancy (DV) pairs. These pairs are responsible for the atomic transport and the formation of DnV clusters that lead to a deactivation of donor atoms. The predictions are technologically significant as they point toward an approach by which V-mediated donor diffusion and the formation of inactive DnV clusters can be suppressed. This would result in shallow and fully electrically active n-type doped regions in Ge-based electronic devices.