Analysis of strain and intermixing in single-layer Ge/Si quantum dots using polarized Raman spectroscopy

The built-in strain and composition of as-grown and Si-capped single layers of Ge/Si dots grown at various temperatures (460-800 degrees 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 degrees C the observations are in agreement with a model of the Ge/Si dot consisting of a Si-rich boundary region and a Ge-rich core.