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 conser vation in Raman scattering for wave vectors both along (q(z)) and perp endicular (q(parallel to)) to the growth direction. In the acoustic-ph onon regime this leads to a continuous emission spectrum which reflect s features of the folded-phonon density of states. Dispersion gaps at centre and edge of the mint Brillouin zone as well as internal gaps at anticrossings of longitudinal and transverse phonon dispersions appea r as pronounced peaks and dips superimposed on the emission background . We analyse the strength of these features in terms of an in-plane sc attering potential and obtain lateral length scales of interface growt h islands. From the comparison of crystal-momentum conserving folded-p honon scattering with the continuous emission signal we determine homo geneous and inhomogeneous broadenings of the electronic structure.