Wurtzite A– and M-plane InN films were grown by molecular beam epitaxy (MBE) on free-standing GaN substrates. Spectroscopic ellipsometry (SE) in the photon energy range from 0.56 up to 15 eV was applied in order to determine the ordinary and extraordinary complex dielectric function (DF) of InN. A distinct optical anisotropy was found over the whole energy range. The extraordinary absorption edge in comparison to the ordinary one is shifted to higher energies confirming previous studies. The investigations in the upper vacuum-ultraviolet (VUV) spectral range (9.5–15 eV) yielded transition energies for four critical points (CPs) of the band structure (BS) which have not been observed so far.
