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 View the MathML source and a perpendicularly applied magnetic field View the MathML source). 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.