Unique hexagonal-Ge nanostructures with direct-bandgap emissions in Si-based light-emitting metasurface

Abstract

Si-based emitters have been of great interest due to their potential as the ideal light source for monolithic optical-electronic integrated circuits (MOEICs) on Si substrates. However, the general Si-based material is a diamond structure of cubic lattice with an indirect-bandgap, which cannot emit light efficiently. Here, unique hexagonal-Ge (H-Ge) nanostructures within light-emitting metasurface consisted of cubic-SiGe nanodisk array are reported. The H-Ge nanostructure is naturally formed within the cubic-Ge epitaxially grown on Si (001) substrates due to the strain-induced crystal phase transition assisted with far-from equilibrium growth conditions. The direct-bandgap features of H-Ge nanostructures are observed and discussed, including a rather strong and linearly power-dependent PL peak around 1560 nm at room temperature, temperature-insensitive PL spectrum above 160 K. Given the direct-bandgap nature and the compatibly with the sophisticated Si technology, the H-Ge nanostructure within a light-emitting metasurface has great potentials for innovative light sources, particularly in Si-based MOEICs.