X-ray rocking curve measurement of composition and strain in Si-Ge buffer layers grown on Si substrates

The level of strain and the fraction of Ge in SiGe layers grown on Si can be found rapidly and unambiguously using double-crystal x-ray diffraction and a simple application of the linear elasticity theory combined with Vegard’s law. The method gives excellent results for 0.4-μm-thick buffer layers of SiGe/Si containing 5%–50% germanium. It is shown that lattice relaxation rises abruptly at x(Ge)≥15%, and that some strain remains for x(Ge) as high as 50%.