Photoluminescence dynamics in GaAs/AlGaAs quantum wells under pulsed intersubband excitation

We investigate the time-resolved photoluminescence (PL) dynamics of an undoped GaAs/AlGaAs multiple quantum well under mid-infrared (MIR) irradiation. A time-delayed MIR laser pulse from a free-electron laser, tuned to the intersubband transition energy of the quantum well, induces temporal quenching of the PL intensity with subsequent recovery. The experimental data can be accurately described by a simple rate-equation model, which accounts for the cooling of the non-radiative states to radiative states. By performing polarization sensitive measurements, we are able to discriminate the contributions of free-carrier absorption from that of intersubband absorption, where the latter is about 50 times more efficient.