|AVS 54th International Symposium|
|Thin Film||Tuesday Sessions|
|Session:||Aspects of Thin Films Poster Session|
|Presenter:||A.K. Jones, University of British Columbia, Canada|
|Authors:||A.K. Jones, University of British Columbia, Canada
A. Ballestad, University of British Columbia, Canada
S. Cheng, University of British Columbia, Canada
T. Li, University of Illinois, Urbana
J. Rottler, University of British Columbia, Canada
T. Tiedje, University of British Columbia, Canada
|Correspondent:||Click to Email|
In order to understand which atom scale processes are important in controlling macroscopic shapes in epitaxial crystal growth, we have simulated the epitaxial growth process numerically, using a kinetic Monte Carlo (kMC) simulation of a restricted solid-on-solid model. Step edge potential barriers (Ehrlich-Schwoebel or ES barriers) are a well-known example of an atomistic property which has an important effect on macroscopic surface morphology. Most theoretical work has concentrated on the effects of positive ES barriers, which are commonly found in metals, and which lead to spontaneous mound formation. In the case of GaAs and probably other III-V semiconductors, epitaxial growth is found to be stable, suggesting a negative ES barrier. In this paper we consider epitaxial growth dynamics for vicinal surfaces with negative ES barriers. In kMC simulations as a function of surface slope we find a "magic slope" with a step density minimum. The step density minimum is caused by the fact that linear arrays of steps are more efficient at capturing adatoms than step edges in the form of loops, thereby reducing island nucleation and step density for small vicinal angles. We show that the step density minimum produces a preferred macroscopic slope similar to a crystal facet but with a different physical origin, in the smoothing of patterned substrates during epitaxial growth. Conventional wisdom1 suggests that in the absence of nucleation, negative ES barriers lead to unstable step edges (step bunching) for 1D vicinal 'surfaces' and positive ES barriers lead to stable step edges (equally spaced steps). In kMC simulations on 2D vicinal surfaces we find a contrary result. In the case of negative ES barriers the steps become evenly spaced and the growth is stable, with or without nucleation. For 2D vicinal surfaces with positive ES barriers, at low temperatures nucleation on top of monolayer islands eventually leads to mounds and unstable growth. If nucleation is turned off, above a critical value of the ES barrier, step edge wandering eventually produces enclosed regions (pits) which do not fill in, which also leads to unstable growth.
1J. Villain, J. de Physique, 1 1991.