Step-motion-imposed asymmetry during molecular-beam epitaxy on vicinal surfaces.

Abstract

Epitaxial crystal growth by molecular-beam epitaxy is frequently described using a modified Burton, Cabrera, and Frank model. Step motion is included in this model through the addition of a convection term and results in an asymmetric density profile across the terraces. The use of macroscopic absorbing boundary conditions at the steps represents an overconstraint since both the kinetics and adatom densities are then equal on both sides of the steps. We make use of a microscopic boundary condition that allows us to properly account for the asymmetry when the steps are absorbing. In the case where the adatom densities at both sides of the steps are equal we determine the relationship that then constrains the step kinetics and obtain specific results for the case where the upstream step is absorbing and the Peclet number is less than 1.