Analysis of strain and intermixing in single-layerGe∕Siquantum dots using polarized Raman spectroscopy

The built-in strain and composition of as-grown and Si-capped single layers of $\mathrm{Ge}∕\mathrm{Si}$ dots grown at various temperatures $(460–800°\mathrm{C})$ are studied by a comparative analysis of the Ge-Ge and Si-Ge modes in the polarized Raman spectra of the dots. A pronounced reduction of the strain and Ge content in the dots after deposition of the cap layer at low temperatures is observed, indicating that strain-induced Si diffusion from the cap layer is occurring. For large dots grown at $700–800°\mathrm{C}$ the observations are in agreement with a model of the $\mathrm{Ge}∕\mathrm{Si}$ dot consisting of a Si-rich boundary region and a Ge-rich core.