Deviation from Vegard law in lattice matched InGaAs/InP epitaxial structures

The lattice parameter and the composition of InGaAs/InP lattice matched single heterostructures have been independently determined by measuring the high resolution X-ray diffraction profile and the absorption of the X-ray beam diffracted from the InP substrate. Mass absorption coefficients taken from recent corrections of values based on relativistic calculation of the X-ray scattering have been used. In contrast with previous work which reported a linear dependence of the lattice parameter with composition, we find a 6% larger In content in the InGaAs/InP lattice matched alloy. The result has been confirmed by X-ray fluorescence of the layer and by analysis of standards made of InAs and GaAs fine ground crystals. The results are in good agreement with the predictions of a simple model of lattice deformation based on elasticity theory.