Single-Crystalline Hexagonal Silicon–Germanium

Group IV materials with the hexagonal diamond crystal structure have been predicted to exhibit promising optical and electronic properties. In particular, hexagonal silicon–germanium (Si 1– x Ge x ) should be characterized by a tunable direct band gap with implications ranging from Si-based light-emitting diodes to lasers and quantum dots for single photon emitters. Here we demonstrate the feasibility of high-quality defect-free and wafer-scale hexagonal Si 1– x Ge x growth with precise control of the alloy composition and layer thickness. This is achieved by transferring the hexagonal phase from a GaP/Si core/shell nanowire template, the same method successfully employed by us to realize hexagonal Si. We determine the optimal growth conditions in order to achieve single-crystalline layer-by-layer Si 1– x Ge x growth in the preferred stoichiometry region. Our results pave the way for exploiting the novel properties of hexagonal Si 1– x Ge x alloys in technological applications.