Intersubband Relaxation Dynamics in Narrow InGaAs/AlAsSb Quantum Well Structures Studied by Femtosecond Pump‐Probe Spectroscopy

Intersubband relaxation dynamics in modulation doped InGaAs/AlAsSb multiquantum well (QW), with different QW thicknesses was investigated by femtosecond pump‐probe Spectroscopy. At early delay times, the samples show an exponential decay of the transient transmission with picosecond time constants. At later delay times, the relaxation dynamics depends on QW thickness. The presence of a slowly decaying component indicates the transfer of electrons to states related to indirect valleys in the barriers. This result is further confirmed by solving three‐level rate equations.