Signatures of Γ ₁-Γ ₅ mixed-mode polaritons in polarized reflectance spectra of ZnO

Theoretical and experimental studies were carried out on exciton-polaritons excited in ZnO. Polaritons in which both Γ ₁ and Γ ₅ excitons couple to electromagnetic waves simultaneously are shown to exist, and their signatures are observed in polarized reflectance spectra measured under k ⊥ a and E∥c configurations for an m-plane sample. Theoretical calculations reveal that the mixed-mode polaritons consist of one Γ ₁ transverse mode and two Γ ₅ longitudinal modes. It is also shown that the signatures are sensitive to the valence band ordering.