CALCULATED PHONON SPECTRA OF Si/Ge SUPERLATTICES : ANALOGIES WITH OTHER SYSTEMS AND NEW FEATURES

Abstract

The phonon spectra of Si/Ge superlattices are calculated along the growth direction. Besides folded and confined modes, as in the more studied case of GaAs/AlAs systems, along (001) they show interface modes in the transverse polarization and resonant modes in the longitudinal one at frequencies just below the edge where the Si and Ge bulk modes start overlapping. The thickness dependence, dispersion and displacement patterns of the latter modes show their similarities to proper confined modes