Femtosecond Reflections of Bulk GaAs and GaAs/AlGaAs Multiple Quantum Wells

We present room temperature femtosecond reflection studies on the photocarrier dynamics of GaAs and GaAs/AlGaAs multiple quantum wells (MQW). A rising wing with a time constant of about 5ps and an increased amplitude per carrier is observed for the MQW sample at carrier densities lower than 5 x 10¹¹cm^-2. This phenomenon is explained as the saturation of the excitonic transitions.