FERMI EDGE SINGULARITY AND SCREENING EFFECTS IN THE ABSORPTION AND LUMINESCENCE SPECTRUM OF SI DELTA-DOPED GAAS

We have investigated single Si-delta-doped layers in GaAs by photoluminescence and photoluminescence excitation spectroscopy (PLE). When the photogenerated holes are confined by GaAs/Al(x)Ga(1-x)As heterointerfaces placed at either side of the doped layer strong radiative recombination is observed from the quasi-two-dimensional electron gas associated with the delta-doping spike. The low-temperature absorption spectrum involving spatially direct transitions, which was measured by PLE, shows a well resolved enhancement at the Fermi edge. The energy position of the absorption edge is found to be independent of the excitation intensity. The peak energy of the band-to-band emission spectrum, in contrast, which involves spatially indirect transitions, shows a shift to higher energies with increasing excitation intensity due to the screening of the space-charge-induced potential by photogenerated carriers.