Study of group-III binary and ternary nitrides using X-ray absorption finestructure measurements

It is demonstrated that the NEXAFS spectra are a "fingerprint" of the symme try and the composition of the binary nitrides GaN, AlN and InN, as well as of their ternary alloys In0.16Ga0.84N and AlyGa1 N-y. From the angular dep endence of the N-K-edge NEXAFS spectra, the hexagonal symmetry of the under study compounds is deduced and the (p(x), p(y)) or p(z) character of the f inal state is identified. The energy position of the absorption edge (E-abs ) of the binary compounds GaN, AlN and InN is found to red-shift linearly w ith the atomic number of the cation. The E-abs of the AlyGa1-yN alloys take s values in between those corresponding to the parent compounds AlN and GaN . Contrary to that, the E-abs of In0.16Ga0.84N is red-shifted relative to t hat of GaN and InN, probably due to ordering and/or phase separation phenom ena. The EXAFS analysis results reveal that the first nearest-neighbour she ll around the N atom, which consists of Ga atoms, is distorted in both GaN and AlxGa1-xN for x < 0.5. (C) 2001 Elsevier Science B.V. All rights reserv ed.