Nonlinear spectroscopy of homoepitaxial GaN

Exciton polaritons from the three uppermost valence bands and the lowest conduction band in homoepitaxial GaN are studied by nonlinear spectroscopy. Second and third harmonic generation and three-photon difference-frequency generation are used to excite resonances on different polariton branches. The resonances show a characteristic polarization dependence, which is consistent with the symmetry assignment of the valence bands.