Defect-free single-crystal SiGe: a new material from nanomembrane strain engineering.

Many important materials cannot be grown as single crystals in bulk form because strain destroys long-range crystallinity. Among them, alloys of group IV semiconductors, specifically SiGe alloys, have significant technological value. Using nanomembrane strain engineering methods, we demonstrate the fabrication of fully elastically relaxed Si(1-x)Ge(x) nanomembranes (NMs) for use as growth substrates for new materials. To do so, we grow defect-free, uniformly and elastically strained SiGe layers on Si substrates and release the SiGe layers to allow them to relax this strain completely as free-standing NMs. These SiGe NMs are transferred to new hosts and bonded there. We confirm the high structural quality of these new materials and demonstrate their use as substrates for technologically relevant epitaxial films by growing strained-Si layers and thick, lattice-matched SiGe alloy layers on them.