Electronic Properties of Strained Si/Ge Core-Shell Nanowires

TL;DR

This study uses first principles calculations to explore how strain affects the electronic properties of Si/Ge core-shell nanowires, revealing band gap reduction and a strain-induced transition from direct to indirect band gap.

Contribution

It provides new insights into strain effects on the electronic structure of Si/Ge nanowires, including band gap tuning and transition mechanisms.

Findings

Band gap of core-shell nanowires is smaller than pure Si or Ge wires.

External tensile strain can induce a transition from direct to indirect band gap.

Strain effects partially counter quantum confinement in nanowires.

Abstract

We investigated the electronic properties of strained Si/Ge core-shell nanowires along the [110] direction using first principles calculations based on density-functional theory. The diameter of the studied core-shell wire is up to 5 nm. We found the band gap of the core-shell wire is smaller than that of both pure Si and Ge wires with the same diameter. This reduced band gap is ascribed to the intrinsic strain between Ge and Si layers, which partially counters the quantum confinement effect. The external strain is further applied to the nanowires for tuning the band structure and band gap. By applying sufficient tensile strain, we found the band gap of Si-core/Ge-shell nanowire with diameter larger than ~3 nm experiences a transition from direct to indirect gap.