CALCULATION OF ENERGIES AND RAMAN INTENSITIES OF CONFINED PHONONS IN SI-GE STRAINED LAYER SUPERLATTICES

We present a fully three-dimensional calculation for the frequencies and the Raman intensities of confined phonons in Si-Ge [001] strained layer superlattices, on a silicon substrate. We take account of the strain in the calculation. The valence force method is used to calculate the phonon frequencies and the related bond polarizability method to calculate the Raman intensities. We predict the fall off of Raman intensity for higher order confined phonons, within both the silicon and germanium layers. We find coupling of transverse interface phonon modes of neighbouring interfaces into even and odd pairs for sufficiently narrow layers. We find that the experimental shape of the Raman spectrum of the interface phonon modes is similar to the density of phonon states. This indicates that interface roughness destroys the k conversation for Raman scattering in the region of the interface phonon modes, similar to Raman scattering from phonons in amorphous materials.