Single-crystalline hexagonal silicon-germanium

Abstract

Group IV materials with the hexagonaldiamond crystal structure have been predicted to exhibit promising optical and electronic properties. In particular,\u3cbr/\u3ehexagonal silicon−germanium (Si1−xGex) 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 Si1−xGex 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 Si1−xGex growth in the preferred stoichiometry region. Our results pave the way for exploiting the novel properties of hexagonal Si1−xGex alloys in technological applications