Raman-Brillouin electronic density in short-period superlattices

International audienceWe analyze and interpret resonant Raman-Brillouin scattering by folded acoustic vibrations in short-period GaAs/AlAs superlattices. Analysis of the spectra and their resonance behavior is performed using a Raman-Brillouin electronic density constructed by combining thousands transitions between electronic eigenstates of the system according to their weight in the light-scattering process. We show that plots of this effective electronic density allow for capturing the essential physics of the electron-phonon interaction and of the resonant light-scattering process in a situation where complex effects are simultaneously present: electronic confinement in the quantum wells and wave-function delocalization due to interlayer coupling, folding of acoustic dispersion and symmetry changes in the deformation fields, resonant selection of optical transitions. Comparison between the measured spectra and those simulated using the Raman-Brillouin quantum model and the photoelastic model are presented. Activation and/or deactivation of the scattering by acoustic vibration doublets and changes in their intensity ratio with excitation energy are directly related to the Raman-Brillouin electronic density distribution along the superlattices axis. Limitations of the photoelastic model are discussed by comparing the steplike variation in the photoelastic coefficient to the Raman-Brillouin electronic density profiles