Low-dislocation-density strain relaxation of SiGe on a SiGeSiGeC buffer layer

We report an observation of strain relaxation in lattice-mismatched heteroepitaxial Si1-x Gex layers, accompanied by a reduction in threading dislocation density (TDD). This occurs on a Si0.77 Ge0.23 layer grown on top of alternating layers of Si0.77 Ge0.23 Si0.76 Ge0.23 C0.01. The present scheme allows us to grow a high-quality 85% relaxed Si0.77 Ge0.23 layer with a TDD of ∼ 104 cm2. The high-resolution transmission electron microscope results showed the presence of Si1-x-y Gex Cy domains (with x≤0.23 and y≤0.01) after annealing at 1000 °C. We infer that the formation of these domains assist the low TDD relaxation by releasing the epitaxial misfit strain as localized discrete strain and by blocking the propagation of misfit dislocations.