Coherent dynamics of excitons in an island-inserted GaAs/AlAs quantum wellstructure: Suppression of phase relaxation and a deep quantum beat

The degenerate four-wave mixing technique in the self-diffraction geometry is employed to investigate a novel GaAs/AlAs quantum well microstructure. T ime-integrated transient measurements are carried out to study the coherent dynamics of excitons in a GaAs quantum well with AlAs islands inserted at the center of the well (IIQW) in excitation densities from 6 x 10(9) to 1.5 x 10(11) cm(-2). The decay of the time-integrated self-diffracted signal s hows slower dephasing for the IIQW compared to that of a normal quantum wel l (NQW) without island insertion. The dephasing rate is found to increase s lightly in the IIQW, while it is found to increase sharply in the NQW with the excitation density. A deep beat with a period of 1.45 ps, which disappe ars for co-circular polarization configuration, is observed in the decay of the self-diffracted signal in the IIQW. The detection-enegy-resolved measu rement reveals that the modulation of the beat increases up to full depth a t low detection energy with respect to the peak energy of the self-diffract ed signal. The dependence on detection energy and on polarization configura tion shows that the beat is a quantum beat due to biexcitonic effect, which is enhanced by localization due to island insertion.