Deviations from Vegard’s rule in Al1−xInxN (0001) alloy thin films grown by magnetron sputter epitaxy

Al 1 − x In x N (0001) thin films of the pseudobinary AlN–InN system were grown epitaxially onto (111)-oriented MgO wafers with seed layers of Ti1−yZryN by dual direct current magnetron sputtering under ultrahigh vacuum conditions. The relaxed film c-axis lattice parameters determined by x-ray diffraction were studied as a function of composition in the range of 0.07<x<0.82 measured by Rutherford backscattering spectrometry. We find a relative deviation by as much as 37% from the linear dependency described by Vegard’s rule for the lattice parameter versus film composition. The highest relative deviations were found at low InN mole fractions, while the largest absolute deviation was found at x=0.63. This shows that Vegard’s rule is not directly applicable to determine the compositions in the wurtzite Al1−xInxN system.