Spatial dispersion effects in the exciton-polariton reflectivity spectra of CuGaS/sub 2/ crystals

The analysis of the exciton reflectivity contour in CuGaS/sub 2/ crystals at 8 K was carried out. Absorption and luminescence spectroscopy was employed for additional characterization. The value of the exciton Ridberg constant /spl Rfr/=0.03247 eV, the energy of the continuum E/sub g//sup n+/spl infin//=2.50305 eV and the thickness of the exciton-free layer L=22 /spl Aring/ were deduced from this analysis. The excited n=2 (2.53323 eV) and n=3 (2.53774 eV) states of the excitons were determined. The upper polariton branch was drawn from the angular dependence of the reflectivity.