Structural, electronic, and optical properties of ⟨001⟩-oriented SiGe nanowires

By means of ab initio calculations, we show that SiGe and Si-Ge core-shell nanowires with the < 001 > orientation and having a diameter of 1.5 nm display a competitive indirect-direct character of the gap. We have also investigated effects of uniaxial strain along the wire axis on the dispersion of the bands close to the gap and the possibility to stabilize the direct band gap. Estimates of the dipole matrix elements of the first direct transition clearly indicate appreciable oscillator strength for SiGe and Ge-core/Si-shell nanowires with dimers on the {001} facets. Our findings can be useful to manipulate electronic and optical properties of such nanostructures being suitable candidates for light emitting devices.