Analysis of X-ray rocking curves from strain relieved heterostructures

Abstract

X-ray diffraction is widely used to analyse the lattice mismatch and the elastic strain in heteroepitaxial semiconductor structures. In this paper we present two sets of practical relations for a routine analysis of Bragg peak spacing in X-ray rocking curves recorded from partly relaxed heteroepitaxial layers on (001) substrates. One procedure is applicable to the case of two asymmetric reflections taken from the same net planes in different diffraction geometries. The second, more general method enables rocking curve data from any net planes to be combined. As an example, a strain relieved SiGe alloy layer on Si(001) is analysed by this method. In both cases the mismatch and the residual layer strain are directly obtained. However, the results obtained from various reflection combinations show a differing strong dependence on any error in the peak separation measurement. This effect is discussed in detail by means of a Si 0.5Ge 0.5/Si model structure. The degree of sensitivity is assessed for a few reflections which are frequently used.