Exciton dimensionality and confinement studied by resonant Raman scattering in GaAs/AlxGa1-xAs Bragg-confining structures and superlattices

The LO-phonon resonant Raman scattering is studied in GaAs/Al0.32Ga0.68As Bragg-confining structures at low temperatures. Comparative studies are made on a GaAs/Al0.32Ga0.68As superlattice and on a bulk Al0.3Ga0.7As crystal. A strong scattering intensity is observed in the spectral range of the (eB:hhB)1S, (eB:lhB)1S Bragg-confined excitions and the (e1:hh1)1S superlattice exciton. The Raman profiles, namely, the scattering intensity versus exciting laser energy (in the respective spectral ranges) are characterized by a large outgoing-beam/incoming-beam intensity ratio. These profiles are analyzed in terms of a model based on exciton confinement, on the anisotropy of its 1S wave function (which defines its dimensionality), and on its scattering by interface and alloy potential fluctuations. The (eB:hhB)1S exciton is thus found to be virtually two-dimensional, while the (eB:lhB)1S and (e1:hh1)1S excitons are intermediate between two and three dimensions. The dimensionality is found to be related to the degree of confinement.