Theory of Ge diffusion during the oxidation of Si/SiGe nano-fins

Recent experimental studies led to the detection of a novel, rapid diffusion of Ge down the sidewall of a Si/SiGe nano-fin structure during high-temperature oxidation. Specifically, the diffusion coefficient for Ge motion along the sidewall is up to five orders of magnitude larger than for Ge diffusion into bulk Si. This enhanced diffusion process can result in the formation of single-crystal Si nanowires embedded in a defect-free SiGe matrix. In this presentation, density-functional-theory calculations are combined with experimental observations to elucidate the atomic-level processes involved in the observed enhanced Ge motion. The calculated energy barriers for Ge motion along the oxidizing interface followed by a reintroduction into the crystalline Si, which results in the formation of SiGe, are consistent with the experimental values.