Simultaneous measurements of electron and hole sweep-out from quantum wells and modeling of photoinduced field screening dynamics

Electron and hole escape times from a GaAs-AlGaAs quantum well in an electric field at room temperature are measured by picosecond optical pump-probe techniques on samples containing a single quantum well in a waveguide. The use of a single well avoids multiple well transport and resonant tunneling effects. Carriers excited in the quantum well by the pump beam result in a transient bleaching signal from excitonic saturation, and, as they leave the well, a transient electroabsorption signal because the movement of charge partially screens the electric field. Both processes are modeled, including important electrical equilibration processes of the sample as a whole. This modeling and the use of two samples with asymmetric barrier heights allows the measurement of the electron and hole emission as a function of applied electric field. Preliminary analysis suggests that the emission mechanism is thermionic rather than by tunneling, but the results are not well explained by conventional thermionic emission models.>