Polariton effect in degenerate valence band semiconductors

Abstract

We present a model which describes excitonic polariton effect for direct gap semiconductors where the valence band is degenerate, so that two (“light” and “heavy”) exciton dispersion curves exist and give rise to three polariton branches. It is shown that the quantity δ = Δ − 1 3 E LT is an important parameter in this case, Δ and E LT being respectively the exchange energy and the longitudinal transverse splitting. A comparison with the available data, extracted from Resonant Brillouin Scattering in GaAs, is carried out. It is shown that when only the uppermost and lowest polariton branches can be detected, the measured separation Δ exp between these two branches is equal to the longitudinal transverse splitting with a good approximation. In the general case the exact relation between Δ, E LT and Δ exp is derived.