Vibrational properties of Si/GaAs superlattices

Raman scattering experiments and first principles phonon calculations have been performed on (Si)m (GaAs)n superlattices grown by molecular beam epitaxy. In spite of the small thickness of the Si layers, folded acoustic modes, confined Si-like and quasi-confined GaAs-like optical modes are clearly observed in the spectra. The experimental frequencies compare well with the calculated ones, confirming that a description of optical phonons in terms of strain- and confinement-induced shifts is appropriate for these novel heterostructures.