Two-photon photocurrent spectroscopy of electron intersubband relaxation and dephasing in quantum wells

Resonantly enhanced nonlinear absorption between conduction subbands in InGaAs/AlGaAs quantum wells induces a two-photon photocurrent under femtosecond excitation, which is exploited to determine electron intersubband relaxation and dephasing times. The approach allows us to study systematically the dependence of these time constants on structural parameters, including carrier density and modulation/well doping, and to discriminate between different scattering processes.