FERMI-EDGE SINGULARITY OF 2-DIMENSIONAL ELECTRONS IN ASYMMETRIC COUPLED DOUBLE-QUANTUM WELLS

We present photoluminescence (PL) and PL excitation investigations on modulation doped GaAs/AlGaAs asymmetric coupled double quantum wells. A Fermi-edge singularity is observed in the emissions between the elec trons in the second sub-band and the holes bound at accepters and in t he valence band. The emission related to the holes bound at accepters in the PL spectra is enhanced remarkably with decreasing excitation po wer for the sample occupied in the second electron sub-band, whereas t his enhancement is much smaller for that which is unoccupied. These be haviours are interpreted as a consequence of the Fermi-edge singularit y caused by the localisation of the holes for the former sample and th e presence of an adjacent unoccupied sub-band for the latter.