Single-Crystalline Hexagonal Silicon-Germanium.

Hauge, Håkon Ikaros T; Conesa-Boj, Sonia; Verheijen, Marcel A; Koelling, Sebastian; Bakkers, Erik P A M · Nano Lett · 2017

basic_science · Level V

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Abstract

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<sub>1-x</sub>Ge<sub>x</sub>) 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<sub>1-x</sub>Ge<sub>x</sub> 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<sub>1-x</sub>Ge<sub>x</sub> growth in the preferred stoichiometry region. Our results pave the way for exploiting the novel properties of hexagonal Si<sub>1-x</sub>Ge<sub>x</sub> alloys in technological applications.