Scattering of polaritons by a two-dimensional electron gas in a semiconductor microcavity

The effect of a classical electron gas on the cavity polariton linewidths is studied experimentally in a GaAs/AlAs microcavity with an embedded quantum well that contains photogenerated electrons (at $T=80\mathrm{}\hspace{0.5em}\mathrm{K}).\mathrm{}$ The linewidth dependence on the electron density and on the cavity mode energy is explained by a theoretical model based on calculating the asymmetric bare exciton line shape, due to electron-exciton scattering. For a given electron density, the exciton line shape is inserted into the linear dispersion theory of the coupled excitons and cavity mode, yielding the reflection spectra that are formed of the three polariton branches. This model reproduces the reduced lower-polariton linewidth and the complex dependence of the middle- and upper-polariton linewidths on the cavity mode energy.