Magnetic field effect on the free electron-exciton scattering in GaAs/AlGaAs bare quantum wells and in microcavities

We report on a detailed study of the free electron scattering effects on the (e1:hh1)1S and (e1:lh1)1S excitons in a GaAs quantum well with a variable density two-dimensional electron gas, that is either bare or embedded in a GaAs/AlGaAs microcavity. These effects are studied by measuring the reflection line width of the bare excitons or cavity polaritons as a function of photoexcitation intensity, temperature (2 < T < 80 K) and a perpendicularly applied magnetic field (0 < B < 7 T). This field induces the formation of charged polaritons at temperatures higher than the range of charged exciton existence without a magnetic field. In order to interpret the line-width data observed at high temperatures, when no charged polaritons exist, we developed a theoretical model that is based on calculating the exciton-electron direct and exchange interaction matrix elements, from which we derive the scattering rates of bare excitons. The model accounts well for the polariton line-widths dependence on microcavity-photon detuning energy and the electron density.