Phonons in self-assembled Ge/Si structures

摘要: Abstract We present the results of an investigation dealing with fundamental vibrations in periodical Ge/Si structures small-size Ge quantum dots (QDs) performed using macro- and micro-Raman spectroscopy under resonant off-resonant conditions. Samples different number repetition Si layers contain QDs average dot base size 15 nm a QD height 2 . Periodic oscillations observed low-frequency region Raman spectra are assigned to folded LA phonons superlattices. The measured phonon frequencies good agreement those calculated Rytov model. These superimposed broad continuous emission originating from whole acoustic dispersion branch due breaking up translational invariance. structure single layer reveal series peaks corresponding localized layer. Using wave vectors is obtained. longitudinal-acoustic velocity determined 8365 ms −1 excellent that derived Brillouin study. In optical range, LO TO observed. position shifts downwards increasing excitation energy (from 2.5 2.7 eV ) indicating presence distribution scattering size-selectively enhanced by resonance exciting laser confined excitonic states.