Fermi-level dependent diffusion of ion-implanted arsenic in germanium

The diffusion of arsenic has been studied in <100> Ge, implanted with 1·1015, 120-keV 75As+ ions/cm2. The implanted samples were subjected to annealing in argon atmosphere in the temperature range of 450-550 deg. C. The annealing times varied between 0.5 and 91 h. The As concentration profiles were measured by secondary ion mass spectrometry. A Fermi-level-dependent diffusion of As atoms was observed and quantitatively explained by diffusion via Ge vacancies with charge states 0 and 2-. The activation energies and pre-exponential factors for As diffusion through neutral Ge vacancies was found to be 3.4±0.3 eV and 2.02x1020 nm2/s, respectively, and through doubly negatively charged vacancies 2.9±0.3 eV and 1.89x1016 nm2/s, respectively. The solid solubility limit of As increases with temperature from about 1x1019 cm-3 at 450 deg. C to about 5x1019 cm-3 at 550 deg. C