Quenching of excitonic optical transitions by excess electrons in GaAs quantum wells

We study quenching of neutral excitonic optical transitions in GaAs quantum wells with increasing excess electron density. This occurs abruptly at ∼${10}^{10}$ ${\mathrm{cm}}^{\mathrm{-}2}$ with the emergence of the negatively charged exciton at lower transition energy. With further increasing density ${\mathit{X}}^{\mathrm{-}}$ evolves smoothly into the Fermi-edge singularity. Polarized magneto-optical spectra confirm our assignment.