Inhomogeneous low temperature epitaxial breakdown during Si overgrowth of GeSi quantum dots

TL;DR

This study investigates how inhomogeneous strain, surface roughness, and growth orientation affect low temperature epitaxial breakdown during Si overgrowth of GeSi quantum dots, revealing facet-dependent stability and mound formation effects.

Contribution

It provides new insights into the mechanisms of epitaxial breakdown on strained surfaces, emphasizing the role of surface facets and mound formation at low temperatures.

Findings

Higher-index facets like {113} reduce breakdown thickness

Surface roughness and mound formation influence stability

Local strain up to 2% has negligible effect

Abstract

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.