Deviation of the AlGaAs lattice constant from Vegard's law

A structure consisting of a multiple quantum well, 10×[GaAs/AlxGa1-xAs], followed by two single layers, AlAs and AlxGa1-xAs, grown on a GaAs substrate by molecular beam epitaxy is studied by x-ray diffraction. Poisson's ratio of AlAs is deduced from the x-ray diffraction data based on two assumptions for the relationship between the AlGaAs lattice constant and its composition. For the first, Vegard's law is assumed and Poisson's ratio is found to be 0.255±0.004, which is much lower than expected ({>}0.31 for III-V semiconductor materials). However, higher values of 0.322±0.004 and 0.328±0.004 are obtained when assuming nonlinear relationships proposed in two previous studies. These high values are in excellent agreement with those obtained by independent measurements. Our results show the deviation from Vegard's law in describing the relationship between the lattice constant of AlGaAs and its composition.

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