Anisotropy of the nitrogen conduction states in the group III nitrides studied by polarized x-ray absorption

The energy distribution of the nitrogen antibonding electron states in the hexagonal epitaxial layers of AlN, GaN, and InN and cubic epitaxial layers of GaN and InN along pxy plane and pz direction is reported. The study was performed by the polarized x-ray absorption at the K edge of N. A strong polarization dependence of the absorption spectra indicating the significant anisotropy of the conduction band was found in the case of hexagonal samples. Very weak polarization dependencies observed in cubic samples correspond well with the defect distribution anisotropy. Qualitatively different and cation dependent antibonding states distribution point out the role played by a contribution of hybridized cation-nitrogen electronic states to the individual conduction band structures of AlN, GaN, and InN.