  Low temperature epitaxial breakdown of inhomogeneously strained Si capping
layers is investigated. By growing Si films on coherently strained GeSi quantum
dot surfaces, we differentiate effects of surface roughness, strain, and growth
orientation on the mechanism of epitaxial breakdown. Using atomic force
microscopy and high resolution cross-sectional transmission electron microscopy
we find that while local lattice strain up to 2% has a negligible effect,
growth on higher-index facets such as {113} significantly reduces the local
breakdown thickness. Nanoscale growth mound formation is observed above all
facet orientations. Since diffusion lengths depend directly on the surface
orientation, we relate the variation in epitaxial thickness to the low
temperature stability of specific growth facets and on the average size of
kinetically limited growth mounds.
