Radiation Enhanced Silicon Self-Diffusion and the Silicon Vacancy at High Temperatures

We report proton radiation enhanced self-diffusion (RESD) studies on Si-isotope heterostructures. Self-diffusion experiments under irradiation were performed at temperatures between $780°\mathrm{C}$ and $872°\mathrm{C}$ for various times and proton fluxes. Detailed modeling of RESD provides direct evidence that vacancies at high temperatures diffuse with a migration enthalpy of $H_V^{\mathrm{m}}=(1.8\pm 0.5)\mathrm{e}\mathrm{V}$ significantly more slowly than expected from their diffusion at low temperatures, which is described by $H_V^{\mathrm{m}}<0.5\mathrm{e}\mathrm{V}$. We conclude that this diffusion behavior is a consequence of the microscopic configuration of the vacancy whose entropy and enthalpy of migration increase with increasing temperature.