Indirect exciton absorption and Raman scattering in GaAs-AlGaAs superlattices

Longitudinal optic (LO) phonon assisted indirect exciton creation (X LO), hot carrier relaxation ((e-h) LO) and Raman scattering phenomena are reported in the optical spectra of GaAs-AlGaAs superlattices. Structures of the same dimensions both with and without double heterostructure confining barriers are studied. For the structures without confining barriers, continuum transitions are suppressed in photoluminescence excitation (PLE) spectra, and as a result the X LO, (e-h) LO and Raman peaks are observed. The X LO absorption peaks are identified from the observation of a clear threshold in PLE at ℏω LO (36.4 meV) above the heavy hole exciton peak. The intensity of X LO is a maximum at 6 meV above the threshold, probably due to dissociation into free carriers at the exciton binding energy (6meV) above ℏω LO. The influence of non-radiative processes on incoherent (PLE) and coherent (Raman) processes is compared.