Evolution of strain and composition during growth and capping of Ge quantum dots with different morphologies

We follow the growth of islands with different shapes by monitoring the strain relaxation by reflection high energy electron diffraction (RHEED). Comparing a bimodal ensemble of pyramids and domes with a monomodal distribution of C-induced domes, we observe different relaxation pathways and a growth mode change from Stranski-Krastanow to Volmer-Weber. We also study the changes induced by the capping process with Si. Small strains in thin cap layers are revealed by spectroscopic ellipsometry. Raman spectroscopy is employed to probe the built-in strain and silicon intermixing in different types of islands, evidencing that smaller islands are enriched in Si and effectively recompressed, whereas bigger relaxed dots remain substantially unaffected