Si1−xGexgrowth instabilities on vicinal Si(001) substrates: Kinetic vs. strain-induced effects

Abstract

A comparative study of kinetically and thermodynamically driven instabilities on vicinal Si(001) surfaces during overgrowth with ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ is reported. We mapped out a wide range of the multidimensional growth parameter space and found, in contrast to previous reports, no evidence for strain-induced step bunching. At low Ge concentrations strain is insufficient to promote strain-induced step bunching, and the modified surface kinetics in the presence of segregated Ge leads to a smoother rather than rougher morphology. High Ge concentrations around 50% could be expected to provide enough strain, but near equilibrium hut cluster formation is the more effective strain-relaxation mechanism. We found the characteristically rippled step-bunching morphology only in a kinetically limited growth regime, where strain is of limited relevance, and in experiments where the SiGe layers replicate an underlying ripple morphology.