Intensity dependence of the Fermi edge singularity in photoluminescence from modulation-doped AlxGa1-xAs/InyGa1-yAs/GaAs heterostructures

A photoluminescence (PL) study of pseudomorphic modulation-doped AlxGa1-xAs /InyGa1-yAs/GaAs heterostructures with high-electron density reveals a fund amental change in the PL spectrum under increased excitation density. The h igh-energy tail of the PL is transformed due to the mutual repulsion of the Fermi-edge singularity (FES) and the excitonic states. The details of this repulsion depend on the excitation density and temperature. At low tempera ture, the dependence of the existence of the FES feature on excitation dens ity has been demonstrated for the first time. The appearance of the FES is accompanied by the formation of an abrupt high-energy edge and occurs at in tensities far below those required for the appearance of the hybridized n=2 exciton. Strong screening of the n=2 exciton state by photoexcited carrier s is observed. The PL behavior under excitation density and temperature var iation near the Fermi edge is explained in terms of a strong effect of the carrier density on the appearance of the FES; the details of this effect ha ve not yet been fully theoretically explored.