Exciton Polaritons in HgI₂ Crystals

Abstract

Abstract At low temperatures a detailed study of the emission and reflection spectra of HgI 2 crystals in the region of the ground state n = 1(Γ −Γ ) exciton resonance has been carried out. It is found that the shape of the resonant exciton emission spectra in allowed and forbidden polarizations E ⊥ c and E ‖, and the relative positions of the emission and reflection spectra are similar to that in many direct gap semiconductors with the high oscillator strength of n = 1 exciton transition. The emission and reflection spectra of the HgI 2 crystals are correlated with the energy structure of the exciton resonance using the polariton model. The interrelation between the resonant exciton emission and the exciton absorption is discussed. The polariton dispersion curves in the region of the n =1 exciton resonance in HgI 2 crystals are calculated on the basis of experimental data.