Two color pump-probe studies of intraminiband relaxation in doped GaAs/AlGaAs superlattices

In this work we investigate the miniband relaxation dynamics of electrons in doped GaAs/AlGaAs superlattices by two-color infrared pump-probe experiments using a free electron laser synchronized to a table top broadband IR source. In contrast to single color experiments, by this technique we are able to separate the different contributions from inter-and intraminiband relaxation to the transient behavior after an ultrafast excitation. In particular, the intraminiband relaxation is studied for different miniband widths, below and above the optical phonon energy of GaAs. For minibands wider than this critical value we find fast relaxation, nearly constant for different excitation intensities whereas for narrow minibands, a strong temperature and intensity dependence of the relaxation is found. The results are in good agreement with previously published Monte Carlo simulations.