Polariton effects in reflectance and emission spectra of homoepitaxial GaN

Reflectance and photoluminescence spectra of exciton polaritons in GaN homoepitaxial layers, grown by metalorganic chemical-vapor deposition on GaN single crystals, are reported. Polariton modes involving excitons $A,$ $B,$ and $C,$ which correspond to split valence bands of Γ₉, Γ₇, and Γ₇ symmetries, are resolved. Energies of the transverse excitons are found to be, respectively: ETA=3.4767eV, ETB=3.4815eV and ETC=3.4986eV, at the temperature T=1.8K. The shape of the measured emission spectra depends upon donor concentration. This is explained in terms of interbranch polariton scattering.