Free electron effects on the cavity polariton linewidth in an AlAs/AlGaAs microcavity containing a two-dimensional electron gas

We report on an experimental study of the microcavity polariton linewidth in an AlAs/AlGaAs microcavity containing GaAs quantum wells (QW) in which a variable density electron gas is photogenerated. The linewidth of the lowest polariton branch shows a clear suppression while that of the other branches show enhancement at narrow detuning energy ranges. A transformation is observed from a strong to weak exciton-cavity mode coupling at a very low photoexcitation intensity.