Measurement of aluminum concentration in epitaxial layers of AlxGa1−xAs on GaAs by double axis x-ray diffractometry

The composition of a series of AlxGa1−xAs layers grown epitaxially by molecular beam epitaxy (MBE) on GaAs has been measured independently by double axis x-ray diffractometry and reflection high-energy electron diffraction. From a quadratic fit to the data, we deduce the lattice parameter mismatch between AlAs and GaAs and the Poisson ratio of AlAs. Asymmetric reflection rocking curves and synchrotron x-ray topography have been used to show that the anomalously low substrate-layer peak splitting for the 1-μm-thick AlAs layer results from relaxation, which is asymmetric. Use of the AlAs rocking curve peak splitting corrected for relaxation yields a mismatch of 1600 ppm (±1%) between AlAs and GaAs, and 0.28±0.01 for the Poisson ratio of AlAs.