Effect of composition on the bonding environment of In in InAlN and InGaN epilayers

We report on the bonding environment of In in InxAl1-xN (0.07<x<0.25) and InyGa1-yN (0.7<y<1) epilayers using extended X-ray absorption fine structure (EXAFS) spectroscopy. The EXAFS analysis reveals that the In-N distance, in both the InAlN and the InGaN ternaries, is only weakly dependent on the In content. Contrary to that, the In-cation distances (in the 2nd nearest neighbour shell) have values closer to those predicted by Vegard's law. More specifically, the distribution of the In-cation distances is bimodal with the ff In-Ga and In-Al distances being smaller than the In-In distance. The variation of the In-Ga and In-Al distances with the In content is in agreement with Vegard's law while the In-In distance deviates from the expected values for In fractions smaller than 0.7. The identified composition-dependent variation of the In-N and In-cation distances, indicates that the alloying induced stress in InAlN and InGaN is mainly accommodated by bond angle variation rather than bond length deformation. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)