Improved assessment of structural properties of ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As/GaAs heterostructures and superlattices by double-crystal x-ray diffraction

The structural properties of ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As/GaAs heterostructures and superlattices grown by molecular-beam epitaxy are investigated in detail using double-crystal x-ray diffraction. The experimental diffraction curves for different symmetric and asymmetric Bragg reflections are analyzed by applying a semikinematical approach of the dynamical theory of x-ray diffraction for distorted crystals. The theoretical fit of the experimental diffraction curves yields detailed information on the strain profile, the chemical composition, and the thickness of heterostructures. We show that the strain and composition as well as the thickness of individual epilayers and the interface quality of superlattices can be determined accurately. No strain and thus no composition fluctuations are found in ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As epilayers grown on GaAs 〈001〉 crystals. Finally, our x-ray diffraction measurements provide further experimental evidence that growth interruption at the transition from AlAs to GaAs, or vice versa, results in atomically abrupt and smooth interfaces of AlAs/GaAs superlattices.