Dynamics and collective properties of non-equilibrium carriers in highly photoexcited quantum wells

The carrier dynamics and the collective properties of a photogenerated quasi-two-dimensional electron gas in an asymmetric undoped GaAs/AlGaAs quantum well (QW) structure are investigated using an all-optical interband pump-intersubband probe absorption experiment. At a carrier density of 1 x 10(12) cm(-2) per QW, an e(1)-e(2) absorption band at 126 meV is found. Transient resonance frequency blueshifts with respect to the single-particle resonance as well as a transient spectral band narrowing are observed. At the carrier density 1 x 10(13) cm(-2) per QW, the e(2)-e(3) absorption band at 99 meV with a spectral width of 5 meV is measured. This band is blueshifted by 30 meV through collective effects and broadened at an excitation density of 3 x 10(13) cm(-2) per QW.