Extended x-ray absorption fine structure studies of InGaN epilayers

The local structure around In atoms in InGaN epilayers grown by Molecular Beam Epitaxy (MBE) and by Metal-Organic Chemical Vapour Deposition (MOCVD) was studied by means of Extended X-ray Absorption Fine Structure (EXAFS). The averaged In fraction of MOCVD grown samples ranged from 10% to 40% as estimated by Electron Probe Microanalysis (EPMA). The In fraction of MBE grown samples spanned the range from 13% to 96%. The In-N bond length was found to vary slightly with composition, both for MBE and MOCVD grown samples. Moreover, for the same In content, the In-N bond lengths in MOCVD samples were longer than those in MBE grown samples. In contrast, the In-In radial separations in MOCVD and MBE samples were found to be indistinguishable for the same In molar fraction. The In-Ga bond length was observed to deviate from average cation-cation distance predicted by Vegard's law for MBE grown samples which indicates alloy compositional fluctuations.