Characterization of Structural Inhomogeneities in GaAs/AIGaAs Superlattices

Abstract

AbstractThin films containing periodic chemical or strain modulation (e.g. artificial superlattices or SL) are often characterized nondestructively by X-ray double-axis diffractometry. The satellite peaks from the modulated structure allow analysis of layer structure, elemental concentration and strain profile. This paper focuses on the effect of layer uniformity on the rocking curves of (001) GaAs/AlxGa1-xAsSL. Double-axis diffractometry for results from MBE samples with 800 Å SL periods and x=0.35 are compared for GaAs/AlGaAs layer thicknesses of 350/450, 400/400 and 450/350 Å. Symmetric (004) and asymmetric (315) diffraction planes are used to measure parallel and perpendicular misfit strains, layer periodicity and aluminum concentration. A modified kinematical scattering model, correcting for absorption and extinction, is used to calculate the satellite peak intensities and spacings. The relative thicknesses of GaAs and AlGaAs and the aluminum elemental concentration are optimized by matching with experimental results. The effect of nonuniform layer thickness on SL peak intensities is also investigated. The experimental results, the modified kinematical scattering calculations and dynamical theory agree closely for the 3-4 /zm thickness layers studied.