Local structure analysis of Ga 1 − x Al x N epitaxial layer

We used the strained-tetrahedron model to interpret published extended x-ray absorption fine structure data on the wurtzite structure of epitaxial GaAlN thin films grown on a sapphire substrate. Site occupation preference coefficients were determined and the nearest neighbor and next-nearest neighbor interion distances were estimated. The three observed ion-pair preference coefficients and the related configuration population coefficients strongly deviate from the random distribution, which indicates that the occurrence of tetrahedra with A 1 l + G 3 a is highly improbable. Moreover, instead of the eight lines expected, the GaAlN phonon spectra display only four strong lines. Finally, the analysis suggests that beyond a concentration of 50% of Al, these thin films grow less homogeneously whatever the method of preparation.