Confinement and electron-phonon interactions of the $E_1$ exciton in self-organized Ge quantum dots

We have utilized resonant Raman scattering to investigate the phonon modes of self-organized Ge quantum dots grown by molecular-beam epitaxy. Both Ge-Ge and Si-Ge phonon modes are found to exhibit strong enhancements at the $E_1$ exciton. The strain in the quantum dots deduced from the phonon energies is consistent with the results of high-resolution transmission electron microscopy. An upper bound on the confinement energy of the $E_1$ exciton in quantum dots was deduced. The enhancement strength in the Si-Ge phonon indicates strong interaction between this mode and the $E_1$ exciton of the Ge dots.