Determination of the lattice parameter and Poisson ratio for AlAs via high-resolution x-ray-diffraction studies of epitaxial films

We have used high-resolution x-ray-diffraction studies of partially relaxed AlAs films grown on GaAs to determine the lattice parameter [5.661 20(6) {} at 300 K, assuming a GaAs lattice parameter of 5.653 25 {}] and the Poisson ratio [0.328(4)] of AlAs. Our results agree with (but are an order of magnitude more precise than) previous AlAs lattice-parameter measurements but contradict recent results obtained from measurements on Alₓ{Ga}_{1{{-}}x}$As films. Properly reinterpreted, the latter measurements, taken together with our results, imply that the ${Al}ₓGa_1-xAs lattice parameter deviates from Vegard's law.