INTERFACE ROUGHNESS AND HOMOGENEOUS LINEWIDTHS IN QUANTUM-WELLS AND SUPERLATTICES STUDIED BY RESONANT ACOUSTIC-PHONON RAMAN-SCATTERING

Acoustic-phonon Raman spectra of GaAs/AlAs superlattices show two char acteristic features: Sharp lines originate in crystal-momentum conserv ing backscattering by folded superlattice phonons. A continuous emissi on background with superimposed peaks and dips is observed due to diso rder-induced scattering from modes of the whole folded acoustic-phonon dispersion. In this case, neither the crystal-momentum component q(z) along q(parallel-to) nor perpendicular to the growth direction is con served. Even in high-quality samples the amount of disorder is such th at both effects appear at the same time. These phenomena allow us to o btain information on growth-related and intrinsic parameters of semico nductor superlattices and multiple quantum wells. Gaps of the folded-p honon dispersion cause intensity anomalies in the background emission. From the ratio of such features at mini-Brillouin-zone boundary gaps, for which only q(z) is not conserved, to those at internal gaps, wher e both q(z) and q(parallel-to) can take arbitrary values, the degree o f interface roughness and the lateral extent of growth islands are ded uced. The resonance behavior of the continuous emission and relative c hanges of wave-vector conserving folded-phonon to background scatterin g intensities are analyzed in terms of homogeneous and inhomogeneous b roadenings of interband critical points. Changes of the homogeneous li newidth with energy and temperature, as well as electron-phonon intera ction constants, are determined.