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

We report room temperature femtosecond time-resolved reflection studies on the carrier dynamics of a bulk GaAs and a GaAs/AlGaAs MQW samples. The experiment was based on a home-made SML Ti: Sapphire laser which delivers 82fs pulses at a repetition rate of 94MHz. Conventional two-beam pump-probe configuration with orthogonal pump-probe polarization geometry was used in the measurements. The reflection change induced on the surface of the sample by the pump pulses was monitored by the time-delayed probe pulses whose reflected intensity was detected by a lock-in amplifier working at differential mode. The samples measured were a bulk GaAs and a GaAs/AlGaAs MQW which consists of five periods of Al0.3Ga0.7As(1000A)/GaAs(100A) sandwiched between a transparent AlGaAs cladding layer and transparent AlGaAs buffer layer grown on a GaAs substrate.