Phonons in Si/Ge superlattices: Theory and experiment

Abstract

The dispersion of longitudinal phonons in Si/Ge superlattices has been calculated using a linear chain model involving first- and second-neighbour interactions. The results of the calculations are compared with the results of Raman experiments on short-period Si/Ge superlattices. The parameters of the model are based on experimental data for bulk silicon and germanium, and on the superlattice parameters determined by X-ray diffraction and Rutherford backscattering spectroscopy. Good agreement between theory and experiment is obtained. The “SiGe” mode observed experimentally is shown to originate from imperfect interfaces.