Intrinsic strain effects on Ge/Si core/shell nanowires: Insights from atomistic simulations

Based on a tight-binding model, we investigate the electronic properties of Ge/Si core/shell nanowires along three growth directions, 〈001〉, 〈110〉 and 〈111〉, with core diameters ranging up to 10 nm. We demonstrate that the band structure strongly depends on the presence of the Si shell and is influenced by the intrinsic strain between Ge and Si layers. Our results suggest that the intrinsic strain counteracts the quantum confinement effects leading to a reduction in the bandgap of the core/shell nanowires. A transition from indirect to direct energy bandgap is observed for 〈001〉 and 〈110〉 orientations. Furthermore, we study the effective mass of the carriers which proves to be very sensitive to the diameter and the orientation of the nanowires.