  We used Raman scattering for study the phonon modes of self-organized Ge/Si
quantum dots, grown by a molecular-beam epitaxy method. It is revealed, that
Ge-Ge and Si-Ge vibrational modes considerably intensify at excitation of
exciton between the {Lambda}3 valence and {Lanbda}1 conduction bands
(transitions E1 and E1+{Delta}1), that allows to observe Raman scattering
spectrum from extremely small volumes of Ge, even from one layer of quantum
dots with the layer thickness of ~ 10 A. It is shown that Si diffuses into the
Ge quantum dots from the Si spacer layers forming Ge_xSi_{1-x} solid solution,
and Si concentration was estimated. It is revealed, that the frequency of Ge-Ge
mode decreases in 10 1/cm at decreasing of the Ge layer thickness from 10 up to
6 A as a result of phonon size confinement effect.
