Characterization of strain in Si1 - xGex/Si Multilayers and superlattices grown by molecular beam epitaxy

A series of strained Si_{1 - x}Ge_x/Si multilayers and superlattices with varying composition x (0.07 < x < 0.33) and layer thicknesses h (5 nm < h < 50 nm) has been grown on Si(100) by Si molecular beam epitaxy both below and above the critical thickness for the formation of misfit dislocations. The structures were characterized with high resolution X-ray diffraction (HRXRD), Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). RBS measurements indicated good crystalline quality of the Si_{1 - x}Ge_x. The (100) minimum yield χ_min was typically 2.6% for the Si and 3.0% for the Ge in the Si_{1 - x}Ge_x. The lattice constants of the tetragonally distorted Si_{1 - x}Ge_x were measured using HRXRD and TEM. These measurements proved that the in-plane lattice constant of Si_{1 - x}Ge_x was equal to that of Si, indicating epitaxial growth. Very large values of the tetragonal strain, up to 2.1% as derived from HRXRD, were measured. RBS ion channelling measurements on the multilayer structures revealed a large influence of the unstrained Si capping layer on the angular position of the Si_{1 - x}Ge_x channelling minimum. The observed strain behaviour as a function of Ge composition could be described by linear elasticity theory. For high Ge concentration, strain relaxation resulted from the generation of misfit dislocations, as was confirmed by plan-view TEM.