Abstract
Self-organized Ge quantum dot (QD) superlattices havingproperties of two- and zero-dimensional structures were investigatedby Raman spectroscopy. Longitudinal optical (LO) Ge phonons, longitudinal(L) Ge-Si phonons and folded longitudinal acoustic (LA) phononssuperimposed on a strong continuous emission were studied underresonant conditions. The measured phonon frequencies of folded LAphonons up to 15th order are in good agreement with thosecalculated using the Rytov model applied usually to planarsuperlattices. The low-frequency continuous emission can beexplained in terms of a breakdown of crystal momentum conservationfor resonant Raman processes involving acoustic phonons. Afrequency enlargement of the continuous emission band and a downwardshift of the LO Ge phonons with increasing excitation energy(2.54-2.71 eV) are attributed to electron and phonon sizeconfinement in the small Ge QDs resonantly contributing to thescattering process. The size of the QDs involved in the process isestimated from analysis of the frequency position of their opticalphonons.
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