First-principles calculations were performed in order to explore the diffusion of excess Si vacancies in the rare-earth silicide ErSi2−x. Nudged elastic band calculations showed that Si vacancies diffused quickly within the Si planes via a site-exchange mechanism with neighboring Si atoms; with a barrier of 0.67eV. Vacancy diffusion across Er planes was more difficult, since the barrier height was nearly 4.4 times larger. This led to a marked anisotropy in Si vacancy diffusion in these 2 directions. When ErSi2−x was grown hetero-epitaxially onto Si(001), the formation energy of a Si vacancy decreased by 22% due to an in-plane expansion of the lattice. The barrier height for vacancy diffusion within Si planes increased by 27% due to the epitaxial strain, while in-plane Si vacancy diffusion was hardly affected. On the other hand, the slower out-of-plane diffusivity was enhanced by the strain but remained small.

First-Principles Simulations of Si Vacancy Diffusion in Erbium Silicide. G.W.Peng, Y.P.Feng, M.Bouville, D.Z.Chi, A.C.H.Huan, D.J.Srolovitz: Physical Review B, 2007, 76[3], 033303 (4pp)