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) Å at 300 K, assuming a GaAs lattice parameter of 5.653 25 Å] 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 ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As films. Properly reinterpreted, the latter measurements, taken together with our results, imply that the ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As lattice parameter deviates from Vegard’s law.