Intersubband relaxation dynamics in semiconductor quantum structures

We monitor the temporal evolution of the electron population in the first and second subband of an undoped GaAs/AlGaAs asymmetric double quantum well after interband optical excitation by using an interband pump/intersubband probe technique. The spacing between the two subbands is smaller than the longitudinal optical phonon energy. We extract an intersubband lifetime of T21 = 100 ps and a recombination time of τ = 410 ps at an excitation density of nS = 8 x 10 cm. Results from a simple rate equation model fit very well to our data.