Exciton absorption saturation by phase-space filling: Influence of carrier temperature and density

We investigate the temporal evolution and the density dependence of exciton bleaching in GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells. We find that the carrier-induced reduction of exciton oscillator strength is not influenced by carrier cooling after creation of hot carriers with femtosecond laser pulses. Excitation density experiments suggest that either phase-space filling or Coulomb screening dominates the exciton bleaching, depending on the carrier density.