Tailoring the character of the band-gap in łangle 011<br />rangle -, łangle 111<br />rangle -~and łangle 112<br />rangle -oriented silicon nanowires

Abstract

The nature of the band-gap in Si nanowires has been investigated by means of ab initio calculations. We show that łangle 011<br />rangle -oriented nanostructures display a direct transition, nanostructures with the łangle 111<br />rangle axis possess a competitive indirect-direct gap character, and nanostructures in the łangle 112<br />rangle orientation are found to have an indirect band-gap. Increasing the lattice parameter along the wire axis leads to the stabilization of the direct transition in the łangle 111<br />rangle -oriented Si nanowires, whereas uniaxial strain does not affect the character of the gap in nanostructures with łangle 011<br />rangle and łangle 112<br />rangle axes. Estimates of the dipole matrix elements in the case of the łangle 011<br />rangle -oriented Si nanowires indicate that their values depend on the surface reconstruction of the 001 facets similar to the nanostructures in the łangle 001<br />rangle orientation.