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Raman studies of interface properties in semiconductor quantum wells and superlattices

Interface roughness and layer thickness fluctuations in superlattices and quantum wells cause a partial breakdown of crystal-momentum conservation in Raman scattering for wave vectors both along (qz) and perpendicular (q||) to the growth direction. In the acoustic-phonon regime this leads to a continuous emission spectrum which reflects features of the foldedphonon density of states. Dispersion gaps at centre and edge of the mini-Brillouin zone as well as internal gaps at anticrossings of longitudinal and transverse phonon dispersions appear as pronounced peaks and dips superimposed on the emission background. We analyse the strength of these features in terms of an in-plane scattering potential and obtain lateral length scales of interface growth islands. From the comparison of crystalmomentum conserving folded-phonon scattering with the continuous emission signal we determine homogeneous and inhomogeneous broadenings of the electronic structure.