Determination of strain in epitaxial semiconductor layers by high-resolution X-ray diffraction

Abstract

For the determination of the strain in structures with only one or two layers on a substrate, rocking curve measurements are sufficient to provide values for the perpendicular and in-plane lattice mismatch as well as the relative orientation of the layer. The author presents new relations for the interpretation of these rocking curves, which do not use the differentiated form of Bragg's law and are therefore also accurate for the interpretation of samples with a large lattice mismatch. Relaxed epitaxial layers give broad peaks in a rocking curve, which are difficult or even impossible to resolve, especially for multilayered structures. The required information can, in those cases, be obtained from a two-dimensional reciprocal lattice map. This requires coupled omega -2 theta scans with a narrow slit in front of the detector. Relations are presented for the direct interpretation of these maps.