Abstract
The structural properties of InGaN have attracted interest on account of therecent widespread use of the material in visible light-emitting devices. A keytopic has been the indirect determination of the composition by x-raydiffraction (XRD). We examine critically the several levels of approximationinvolved in this procedure. It is shown by extended x-ray absorption finestructure (EXAFS) measurements that the local structure of InGaN is independent of the composition, in the range of InN fraction, from about 15to 40%, that corresponds to blue to infrared light emission from thismaterial. EXAFS-determined ratios of the numbers of indium and gallium atomsin the first metal co-ordination shell, M1, show very good agreement with thecomposition measured by established techniques, both structural and chemical,on similar samples. On the other hand, the atomic separations deviate markedlyfrom values calculated using Vegard's law. In particular, the average radialseparations, In-N1=2.11(2) Å and In-M1=3.28(3) Å, donot vary significantly with In/Ga ratio in the examined composition range. Weconclude with some brief comments on the uncertain but challenging topic ofInGaN nanostructure.
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