Optical responses of exciton-polaritons confined in thin GaAs AlGaAs coupled multi-quantum-well layers

We have measured the Brewster angle reflection spectra of thin GaAs layers and GaAs/Al0.3Ga0.7As coupled multi-quantum-wells (coupled-MQW) layers. The reflection spectra for the GaAs thin layers showed clear peaks correspondi ng to energies of exciton-polaritons quantized in the layers. This means th at exciton translational motion along the normal direction of the layer is coherently extended and quantized due to the confinement within the layer. We observed, moreover, remarkable thickness dependence of the spectra. For the GaAs/Al0.3Ga0.7As coupled-MQW layers, the reflection spectra also show a similar spectra indicating the quantized exciton-polariton peaks. This in dicates a coupled-MQW layer is successfully grown with a high quality almos t same as a simple GaAs layer in which the coherency of free excitons exten ds over a whole layer. (C) 1999 Elsevier Science B.V. All rights reserved.