Strain and Phonon Confinement in Self-Assembled Ge Quantum Dot Superlattices

Raman scattering measurements were carried out in self-assembled Ge quantum dot superlattices grown by molecular beam epitaxy. The characteristics of the Ge-Ge, Si-Ge, Si-Si_LOC and Si-Si peaks were investigated, especially the Ge-Ge optical phonon frequency shift was emphasized, which was tuned by the phonon confinement and strain effects. The experimentally observed frequency shift values of the Ge-Ge peak frequency caused by optical phonon confinement and strain in Ge quantum dots were discussed with quantitative calculations.