Raman Scattering From Zone-Folded Acoustic Phonons In Periodic And Quasiperiodic Superlattices

Raman scattering measurements of zone-folded acoustic phonons in periodic and quasiperiodic superlattices have been performed and analyzed in order to extract values of the structural parameters. The period of either periodic or quasiperiodic lattices can be obtained with an accuracy of 2-3% from analysis of the peak frequencies. The determination of the period can be made accurately even in strained-layer material systems which exhibit misfit dislocation networks. Peak intensity analysis yields an estimate for the individual layer widths, but with considerably more uncertainty than found using x-ray diffraction modeling. In strained-layer lattices intensity analysis is generally limited to structures which exhibit pseudomorphic epitaxy since the presence of misfit dislocation arrays perturb the zone-folded acoustic mode intensities. In lattices grown with intentionally broken symmetry we have observed strong zone-boundary peaks which would normally be symmetry forbidden. Observation of the latter serve as a qualitative indicator of layer width variations in superlattices.