RAMAN-SCATTERING FROM FOLDED PHONON-DISPERSION GAPS

We study the consequences of interface roughness on folded acoustic phonon Raman spectra in GaAs/AlAs quantum wells and superlattices. Layer thickness fluctuations cause a partial breakdown of crystal momentum conservation along and perpendicular to the growth direction. Folded phonons from the whole minizone contribute to a continuous Raman background with intensity anomalies at zone edge and internal dispersion gaps. The observations are explained by invoking the dependence of the Raman efficiency on crystal momentum. Typical length scales of interface roughness are determined.