Strain Adjustment in Si / SiGe Superlattices by a SiGe Alloy Buffer Layer

Strain distribution in a strained layer superlattice on Si can be adjusted by epitaxial insertion of a strain relieved homogeneous buffer layer between the substrate and the superlattice. We report on the strain relief in alloy buffer layers with as a function of layer thickness. The layers are grown by molecular beam epitaxy on (100) Si substrates at 450°C. X‐ray diffraction, transmission electron microscopy, and Rutherford backscattering are applied to the film analysis. Above a critical thickness, i.e. , the onset of strain relief, in a first range a strong decrease of film strain by formation of misfit dislocations is observed followed by a saturation‐like branch with only a weak strain thickness dependency. A residual strain of about 1/3 of the lattice mismatch is found at a thickness of five times the critical one.