Symmetry of excitons in GaN

Magnetoreflectivity measurements on GaN are used to resolve the symmetry of three excitonic resonances, arising from the crystal-field and spin-orbit effects on the valence band. The symmetry characteristic for each valence subband is directly seen in the observed Zeeman pattern. The linear magnetic-field effect for all exciton components is well accounted for by introducing only two coupling constants: the electronic g factor for the conduction band and the Luttinger $\ensuremath{\kappa}$ parameter for the valence band. The strength of the electron-hole exchange interaction is determined.