Reflectivity of two-dimensional polaritons in GaAs quantum wells

A very large absolute reflectivity (>70%) near the exciton resonance is reported for single GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells. The large reflectivity persists at lattice temperatures greater than 100 K. The reflectivity of single quantum wells is shown to be a function of the intrinsic radiative lifetime and the scattering rate of excitons with phonons and impurities. The macroscopic two-dimensional exciton polarization is well described by a microscopic model of nonlocal susceptibility. Based on the magnitude and width of the reflectivity peak, we deduce a value for the radiative linewidth of the free exciton which is in good agreement with the values obtained from radiative lifetime measurements.