Monte Carlo studies of intersubband relaxation in wide GaAs/AlGaAs quantum wells

Using an ensemble Monte Carlo simulation, we have investigated intersubband relaxation of photo-excited electrons in GaAs/AlGaAs quantum wells having a subband spacing smaller than the polar optical phonon energy. A comparison is made to recent time-resolved pump and probe experiments performed on both uniformly doped and modulation doped quantum wells under bleaching conditions in which good agreement between theory and experiment is obtained. Our results show that in uniformly doped samples the decay of electrons is limited by ionized impurity scattering during the photoexcitation process. Polar optical phonon emission also contributes considerably to the electron decay. In modulation doped samples, polar optical phonon scattering controls the decay with a strong contribution through intercarrier scattering. Impurity scattering is responsible for a faster relaxation of the electron system towards a quasi-equilibrium distribution in uniformly doped quantum wells after the pump pulse has ended.