Deviations from Vegard's rule in Al_1-xIn_xN (0001) alloy thin films grown by magnetron sputter epitaxy

Al_1−xIn_xN (0001) thin films of the pseudobinary AlN–InN system were grown epitaxially onto (111)-oriented MgO wafers with seed layers of Ti_1−yZr_yN 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 Al_1−xIn_xN system. © 2007 American Institute of Physics.
[DOI: 10.1063/1.2450675 ]