Optical polariton modes in a nanoscale semiconductor

Because of the existence of an exciton-biexciton transition inside an optically excited semiconductor, the dielectric constant is modified to be a wave-vector-dependent function. The spatial dispersion relation leads to three propagating modes of polariton, for which two additional boundary conditions will be required. In the vicinity of a resonance, the mathematical study shows that two modes among the three dominate, and the third wave with a large imaginary part can be neglected without affecting the essential physics. Based on the study, a criterion is developed for selecting the appropriate modes. Numerical results are presented for a thin semiconducting film.