Femtosecond pump-probe spectroscopy of intersubband relaxation dynamics in narrow InGaAs/AlAsSb quantum well structures

Intersubband relaxation dynamics in InGaAs/AlAsSb multiquantum wells (QWs) is studied by single-color femtosecond pump-probe measurements. At early delay times, all samples show an exponential decay of the transient transmission occurring with time constants of the order of a picosecond. The relaxation dynamics at later delay times strongly depend on both QW thickness and doping location. A non-single-exponential decay behavior indicates extra competing relaxation channels, as further confirmed by solving three-level rate equations. It is shown that slowly decaying components are due to electron transfer to states related to indirect valleys in the wells or in the barriers. (c) 2006 American Institute of Physics.