Calculated Schwoebel barriers on Si(111) steps using an empirical potential.

Abstract

Motivated by the recent investigations on instabilities caused by Schwoebel barriers during growth and their effects on growth or sublimation by step flows, we have investigated, using the Stillinger-Weber potential, how this step edge barrier arises for the two high symmetry steps on 1$\times$1 reconstructed Si(111). Relative to a barrier of 0.97 $\pm$ 0.07 eV on the surface, we find additional (Schwoebel) barriers of 0.61 $\pm$ 0.07 eV and 0.16 $\pm$ 0.07 eV for adatom migration over the [$\overline{2}11$] and the [$\overline{1}\overline{1}2$] steps respectively. The adatom potential energy is found to be strongly correlated with that derived from the local geometry of atoms on the adatom-free surface or step edges. This correlation preserves a strict correspondence between the barrier determining features in the spatial variation of the adatom potential energy and the same derived from the local geometry for the Si(111) surface and the [$\overline{2}11$] step. It is therefore argued that the Schwoebel barrier on the [$\overline{2}11$] step is robust {\it i.e.} a feature that would survive in more satisfactory {\it ab initio} or tight binding calculations. Using a diffusion equation for the adatom concentration the relevance of the barrier to electromigration of steps has been explored. Data from such experiments on Si(111) has been used to place an upper bound on the Schwoebel barrier and a lower bound on the electromigration force.