Determination of epitaxic-layer composition and thickness by double-crystal X-ray diffraction

Abstract

Double-crystal X-ray diffraction rocking curves can be used to evaluate composition and thickness of epitaxic layers. In order to assess the limits of this technique, the 004 rocking curves of molecular-beam epitaxy- (MBE) grown coherent AlGaAs/GaAs epitaxic layers have been measured. The composition was calculated both by using theoretical values for the lattice parameters of the limiting compositions together with Vegard's law and also by using an epitaxic layer of AlAs as an in situ standard. The accuracy of this concentration measurement is evaluated by comparing it with an independent measurement of the composition. MBE-grown AlxGa1 − xAs (x = 0.3, 0.5, 0.7) epitaxic layers in the thickness range 0.2–6.0 μm were used to investigate the usefulness of the X-ray rocking-curve method for layer thickness measurement. The experimental rocking curves are compared with those generated from computer simulations based on X-ray dynamical scattering theory. In the thickness range 0.5–2.0 μm Bragg-geometry Pendellösung fringes are also observed. The layer thicknesses calculated from the integrated intensity ratios and the fringe spacings agree with layer thicknesses obtained from scanning electron microscope (SEM) sections. The applicability of this method to multiple layers is investigated using test structures.