Center-of-mass quantization of excitons and Fabry–Perot modes of the polariton in ZnSe epilayers

Reflectance properties of ZnSe epilayers grown on GaAs substrates are studied at 80 K. Oscillation features are observed in the region of exciton resonance which are significantly different depending on the epilayer thickness L. For optically thin layers with thickness in the range of several tens of nanometer, reflectance oscillations appear above the light-hole (lh) exciton, while for optically thick layers with thickness in the range of a micrometer, reflectance oscillations appear between 1s and 2s excitons. These oscillations are interpreted as the quantized levels of the exciton center-of-mass motion in the lower branch of the polariton for optically thin layers and Fabry–Perot modes in the upper branch of the polariton for optically thick layers, respectively. The reflectance data are analyzed in the frame work of a dielectric function with a polariton dispersion.