Characterization of GaAs/Si interface structure by x ray diffraction

By measuring the intensity profiles along the crystal truncation rods of a Si(001) substrate, we obtain the depth sensitivity necessary for x ray diffraction measurements of the structure of its interface with a thick GaAs overlayer which is epitaxial to, but not in registry with the substrate. By comparing the diffraction with a model based on a grid of misfit dislocations, we find that the atoms at the interface have a root mean square displacement of 1.09 +/- 0.1 A from this ideal structure, and that the interface has a roughness of 2.9 +/- 1 A. The diffraction indicates an anomalously small strain perpendicular to the interface in the GaAs near the interface.