Le Journal de Physique IV 03 (1993) C5-389-C5-392
Excitonic polariton interference in the reflectance of GaAs thin filmsA. TREDICUCCI1, Y. CHEN1, 2, G . CZAJKOWSKI1, 3 and F. BASSANI1
1 Scuola Normale Superiore, P.zza dei Cavalieri 7, 56126 Pisa, Italy
2 Laboratoire de Microstructures et de Microélectronique, CNRS, 196 avenue Henri Ravera, 92220 Bagneux, France
3 Department of Physics II, Academy of Technology and Agriculture, Kaliskiego 7, 85790 Bydgoszcz, Poland
We have investigated the reflectivity of GaAs thin layers in the excitonic absorption region, observing detailed interference structures which reveal the polariton dispersion and the quantization of the exciton centre-of-mass motion. To analyse the experimental spectra, we have calculated the optical properties of thin films using a real-space density-matrix approach adapted to the case of degenerate valence bands. The oscillatory behaviour of the reflectance is well reproduced ; a surface layer where the polarization decreases to zero is computed and its thickness is found to be energy dependent. The temperature dependence shows a broadening of the fine structure due to the phonon interaction and a decoupling of excitons and photons at high temperature.
© EDP Sciences 1993