Annealing studies of high Ge composition Si/SiGe multilayers

Abstract

Abstract For the design flexibility of SiGe based quantum cascade lasers high Ge composition Si/SiGe (x = 80%) superlattices are important. We present an X-ray small angle scattering and high-resolution X-ray diffraction study on strain compensated Si/Si1– x Gex multiple quantum well structures with Ge compositions (x up to 80%), grown on Si0.5Ge0.5 pseudo-substrates. To test the temperature stability of such layers occurring in processing steps, in-situ annealing X-ray reflectivity measurements were performed for temperatures up to 810 °C. From the analysis of the reflectivity data, we obtain the layer thicknesses and the interface roughness of the superlattices during annealing. Using a one dimensional diffusion equation, the Ge diffusion coefficient for these conditions was obtained. Furthermore, the strain status and Ge composition in the superlattice structure and in the SiGe buffer before and after annealing were determined from the symmetrical and asymmetrical reciprocal space maps.