REFLECTIVITY OF GAAS THIN-FILMS - DENSITY-MATRIX STUDY OF POLARITON INTERFERENCE AND OF EXCITON MOTION QUANTIZATION

An accurate study of the optical properties of GaAs thin layers in the excitonic absorption region, obtained with a real-space density-matrix approach adapted to the case of thin films with degenerate valence bands is reported. The computed polarization decreases gradually to zero near the surfaces in a transition layer whose thickness decreases with increasing photon energy. The oscillatory behaviour of the reflectivity is well reproduced and can be interpreted in terms of polaritonic effects by relating the dispersion of the propagating modes to the calculated spectra. The effect of the confining material on the lineshapes and on the intensity of the peaks is also explained.