The phonon modes of self-assembled Ge/Si quantum dots grown by molecular-beam epitaxy in an apparatus integrated with a chamber of the scanning tunnelling microscope into a single high-vacuum system were investigated using Raman spectroscopy. It was revealed that the Ge-Ge and Si-Ge vibrational modes were considerably enhanced upon excitation of excitons between the valence band Λ3 and the conduction band Λ1 (the E1 and E1 + Δ1 transitions). This made it possible to observe the Raman spectrum of very small amounts of Ge, such as one layer of quantum dots with a Ge-layer thickness of  some 10Å. The enhancement of these modes suggested a strong electron-phonon interaction of the vibrational modes with the E1 and E1 + Δ1 excitons in the quantum dot. It was demonstrated that the frequency of the Ge-Ge mode decreased by 10/cm with a decrease in the thickness of the Ge layer from 10 to 6Å; due to the spatial-confinement effect. The optimum thickness of the Ge layer for which the size dispersion of quantum dots was minimal was determined.

The Role of Interdiffusion and Spatial Confinement in the Formation of Resonant Raman Spectra of Ge/Si(100) Heterostructures with Quantum-Dot Arrays. I.V.Kucherenko, V.S.Vinogradov, N.N.Melnik, L.V.Arapkina, V.A.Chapnin, K.V.Chizh, V.A.Yurev: Physics of the Solid State, 2008, 50[10], 1970-7