Determination of interface coherency by x-ray double-crystal diffraction

The degree of coherency at the interface between an epitaxial layer and a substrate or between two different epilayers is defined as a coherency factor fCOH. By performing just three diffraction measurements on an x-ray double-crystal diffractometer and calculating the deformations of the corresponding epilayer according to the peak separations, this coherency factor can be determined together with the composition of the epilayer on any orientation substrate. The experimental results show that the coherency factor at the interface varies significantly with the composition and thickness of the epilayer for a system with large misfit, so the determination of the coherency factor is necessary for the calculation of the epilayer composition via the relaxed lattice constant.