FERMI-EDGE SINGULARITY IN EXCITONIC SPECTRA OF MODULATION-DOPED ALGAAS GAAS QUANTUM-WELLS/

The dynamic response of an electron Fermi sea to the presence of optic ally generated holes gives rise to an enhanced interaction of correlat ed electron-hole pairs near the Fermi level, resulting in an enhanced oscillator strength for optical transitions, referred to as the Fermi- edge singularity. We studied this effect in modulation-doped quantum w ells which provide confined dense Fermi sea, spatially separated from dopant atoms, easily accessible for investigations under low excitatio n conditions. The Fermi-edge singularity was observed in both photolum inescence and photoluminescence excitation experiments, although in th e case of photoluminescence the samples had to be either co-doped with accepters in the wells to provide necessary localization of holes or designed to allow for nearly resonant scattering between the electroni c states near the Fermi energy and the next unoccupied subband of tile 2D electron gas.