Analysis of the local structure of InN with a bandgap energy of 0.8 and 1.9 eV and annealed InN using X-ray absorption fine structure measurements

We compared the local structure around In atoms in microwave-excited MOCVD- and MBE-grown InN film which indicates an absorption edge at 1.9 and 0.8 eV, respectively. The co-ordination numbers of the 1st-nearest neighbor N atoms and the 2nd-nearest neighbor In atoms for MBE-grown InN were n(N)=3.9±0.5 and n(In)=12.4±0.9, which are close to the ideal value of n(N)=4 and n(In)=12 for InN without defects, respectively. By thermal annealing, the structure of MBE-grown InN was changed from InN to In2O3, and the absorption edge was changed from 0.8 to 3.5 eV. However, the microwave-excited MOCVD-grown InN had no structure of In2O3, and had the reduced co-ordination numbers of the 2nd-nearest neighbor In atoms of n(In)=10.6-11.7. From these results, we conclude that the origin of the 1.9-eV absorption edge of InN is the imperfections (defects) of the In lattice sites of InN, rather than the generation of In2O3, which has a bandgap energy of 3.5 eV. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)