Radiation enhanced diffusion in germanium

Ge isotope heterostructures were irradiated with 2.5 MeV protons at temperatures between 550°C and 640°C. The applied proton flux was varied up to 3.8 μA per cm². Secondary ion mass spectroscopy (SIMS) was utilized to record concentration profiles of the Ge-isotopes after the irradiation treatment. The SIMS profiles show a homogenous broadening of the multilayer structure. Continuum theoretical simulations were performed which are based on diffusion models that consider the formation of Frenkel-defects and their annihilation. Best fits to the experimental profiles are obtained when the boundary conditions for vacancies and self-interstitials are assumed differently. Ge self-interstitials are reflected at the surface, whereas the concentration of Ge vacancies approaches the thermal equilibrium value. To check these boundary conditions, experiments on the diffusion of n-type dopants under irradiation were performed.