Intersubband relaxation dynamics in single and double quantum wells based on strained InGaAs/AlAs/AlAsSb

Intersubband relaxation dynamics in single and coupled double quantum well (QW) structures based on strained InGaAs/AlAs/AlAsSb are studied by femtosecond pump probe spectroscopy at wavelengths around 2 um. For single QWs the transient transmission was observed to decay exponentially with a time constant of 2 ps, showing that side valleys have negligible influence on the intersubband relaxation dynamics for strained InGaAs QWs. For double QWs, the pump-probe signal at the intersubband energy involving the two electronic levels located at the wider QW exhibits an induced absorption component attributed to the population of the second subband (associated with the narrow QW) by hot-electrons.