Calculated phonon spectra of Si/Ge (001) superlattices: Features for interface characterization

We present a model calculation or phonon spectra of Si/Ge superlattices along the (001) growth direction. The most relevant result for structural characterization is that interface modes involving the SiGe bonds at the interface are predicted only in the transverse and not in the longitudinal polarization. The detection of such modes between the Si-like and Ge-like optical modes in backscattering Raman spectra from the (001) surface must then be ascribed to interface disorder or alloying.