High Resolution X-Ray Diffraction

Abstract

Conventional high resolution X-Ray diffraction has been developed into a powerful tool for the nondestructive ex-situ investigation of epitaxial layers, of heterostructures and superlattice systems: The information which is obtained from diffraction patterns concerns the composition and uniformity of epitaxial layers, their thicknesses, the built-in strain and strain relaxation, and the crystalline perfection related to their dislocation density. Furthermore information on interfaces like interdiffusion and intermixingis obtained under certain circumstances as well. For the analysis of the diffraction patterns from epilayers, heterostructures and multilayers, the kinematical diffraction theory, although being still useful for a quick inspection of the data, in general can no longer be used for the quantitative description of the experiments. Instead dynamical theory is applied which takes into account extinction, multiple scattering, and the slight deviation of the refractive index from one. The instrumentation has also been improved continuously and simple powder diffractometers using a focussing path for the X-Rays were replaced by double- and triple -axis spectrometers equipped with multiple crystal or channel cut monochromators and analyzers. Apart from investigations under normal Bragg conditions grazing angle incidence techniques both for the determination of layer thicknesses as well as for precise information on lattice constants of thin films have also been employed. X-Ray topography is used for imaging purposes of layers grown on large wafers.