Diffusion of As into Ge from a GaAs overlayer deposited on p-type Ge substrates has been studied by means of secondary ion mass spectrometry. A concentration-dependent diffusion of As atoms was observed in addition to the concentration-independent diffusion of Ga and As atoms. The concentration dependence is explained by a Fermi-level-dependent diffusion model. Arsenic atoms are shown to diffuse through Ge vacancies with the charge states 2− and 0. No presence of the singly negatively charged vacancies was observed, indicating that Ge vacancy could be a negative U center.
Vainonen-Ahlgren, E., Ahlgren, T., Likonen, J., Lehto, S., Keinonen, J., Li, W., & Haapamaa, J. (2000). Idenfication of vacancy charge states in diffusion of arsenic in germanium. Applied Physics Letters, 77(5), 690 - 692. https://doi.org/10.1063/1.127087