EXCITONIC ENHANCEMENT OF THE FERMI-EDGE SINGULARITY AND RECOMBINATIONKINETICS OF PHOTOGENERATED ELECTRONS IN P-TYPE DELTA-DOPED GAASBE AL(X)G(1-X)AS DOUBLE-HETEROSTRUCTURES/

We have studied the photoluminescence (PL) spectrum, and the strength of the Fermi edge singularity (FES) in that spectrum, of the two-dimen sional hole gas (2DHG) formed in GaAs/AlxGa1-xAs double-heterostructur es as a function of the width of the GaAs layer, the centre of which i s p-type delta-doped. A variation of that layer width allows us to tun e, for a fixed doping concentration, the energetic spacings between th e hole subbands. From these experiments, we conclude that the observat ion of a FES in the PL spectrum of a 2DHG is brought about by a resona nt hybridization between occupied states close to the hole Fermi energ y and exciton levels involving nearby lying unoccupied hole subbands. The recombination and spin-flip scattering times of the photogenerated electrons are found to decrease drastically with decreasing GaAs laye r width which reflects the increase in the electron-hole wavefunction overlap.