Optical phonons in self-assembled Ge quantum dot superlattices: Strain relaxation effects

Abstract

We present Raman scattering by optical phonons in self-assembled Ge quantum dot superlattices grown by solid-source molecular beam epitaxy. The Ge quantum dots are vertically correlated and have different average sizes and dot morphologies. The GeGe optical phonon frequency was mainly caused by strain relaxation effects. Experimentally observed GeGe optical phonon modes were compared with calculated values using the deformation potential theory, indicating that the strain relaxation of Ge quantum dot superlattices arises not only from atomic intermixing but also from the morphology transition in dot formation.