Microscopic Theory of Atomic Diffusion Mechanisms in Silicon

We report self-consistent Green's-function total-energy calculations which provide, for the first time, a firm theoretical framework for understanding the microscopic mechanisms of atomic diffusion in Si. We find that the self-interstitial has negative-U properties, roughly the same formation energy at several sites, small migration barriers, and charge-state instabilities that allow athermal migration along several paths. We also find that both vacancies and interstitials mediate self-diffusion and reconcile contrasting low- and high-temperature data.