Evaporation and impingement effects on drift-induced step instabilities on a Si(001) vicinal face

Abstract

We theoretically study the effect of evaporation and impingement of atoms on step wandering induced by the drift of adatoms. With a Si(001) vicinal face in mind, the anisotropy in diffusion coefficient is assumed to alternate on consecutive terraces. Without evaporation, steps wander in-phase with step-up drift and grooves perpendicular to the steps appear. The form of the wandering steps is sinusoidal with the width increasing in time as ${t}^{1∕2}$. Evaporation of adatoms suppresses the step wandering and introduces two surface diffusion lengths. When they are longer than the step distance, the step width still increases in proportion to ${t}^{1∕2}$, but with a smaller coefficient than that in the case without evaporation. When one of the surface diffusion lengths is comparable or shorter than the step distance, the saturation of the step width occurs. Impingement of atoms, on the other hand, changes the form of the wandering steps: their front becomes flat and wide and the grooves become steep and narrow. The growth rate of the step width becomes small, but the step width increases with the same exponent $1∕2$.