Substrate engineering by hydrogen or helium implantation for epitaxial growth of lattice mismatched Si1-xGex films on silicon

Strain relaxed Si_1-xGe_x layers on Si(100) are used as virtual substrates for the growth of, for example, Si/Si_1-xGe_x quantum well structures. We investigated the effects of He⁺ ion implantation and subsequent annealing on pseudomorphic Si_1-xGe_x/Si(100) heterostructures grown by molecular beam epitaxy (MBE). A narrow defect band was generated by ion implantation slightly underneath the interface inducing the formation of strain relieving misfit dislocations during subsequent thermal annealing. Nearly complete strain relaxation of Si_1-xGe_x layers with Ge fractions up to 30 at.% was obtained at temperatures as low as 850°C and the samples appeared free of threading dislocations within the SiGe layer to the limit of transmission cross-sectional electron microscopy. We thus have developed a method for producing high-quality, thin, relaxed Si_1-xGe _x films on Si(100) with threading dislocation densities below 10⁷ cm^-2 by standard techniques as molecular beam epitaxy and ion implantation. The heterostructures were analyzed using X-ray diffraction, Rutherford backscattering/channeling spectrometry and transmission electron microscopy