Spectral properties of InN and its native oxide from first principles

Electronic single, and two-particle excitations and their influence on electron, optical, and X-ray spectra are studied by ab initio methods and discussed in the light of experiments for InN and its native oxide In2O3. The theoretical approaches are based on iterative solutions of the quasiparticle equation. The resulting gaps for InN and In2O3 are close to experimental data. The total density of states (DOS) explains the XPS measurements. There is excellent agreement between site-and orbital-projected DOS and X-ray absorption spectra. The rigid shift between theory and experiment is identified as core exciton binding energy. The inclusion of excitonic effects yields optical spectra whose lineshapes are in agreement with the measured peak structure. Our computational method possesses an accuracy that allows the prediction of binding energies E-B in the rneV range for Wannier-Mott excitons. For InN we predict EB < 5 meV. The parameter-free methods give the energy gaps of the different In2O3 polymorphs and explain the so-called indirect gap by interconduction band transitions. The band alignment using the branch-point energy yields band discontinuities resulting in a type-I heterostructure. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim