Microscopically resolved resonant Rayleigh scattering from single excitons

Strongly disordered GaAs/AlGaAs quantum wells (QW) have been excited resonantly with a narrow bandwidth cw laser which was scanned over the absorption profile of the QW. The secondary emission of the QW was investigated with microscopic resolution using either a CCD, examining the spatial distribution of the emission, or an imaging CCD spectrograph. The observed resonant emission was found to be very well isolated spectrally as well as spatially. From comparison with numerical model calculations it was found that spectrally sharp emission peaks clearly can be assigned to single excitons. However, spatially isolated emission spots do not prove strong localization of the emitting excitons.