Electronic and structural properties of rhombohedral [111] and [110] oriented ultra-thin bismuth nanowires

TL;DR

This study uses density functional theory and GW approximation to analyze the electronic properties of ultra-thin rhombohedral bismuth nanowires, revealing size-dependent band gaps and surface effects for different orientations.

Contribution

It provides detailed insights into the quantum confinement effects and surface passivation requirements of [111] and [110] bismuth nanowires, including band gap predictions at nanometer scales.

Findings

[111] nanowires require surface saturation to avoid metallic states.

Quantum confinement induces band gaps of ~0.5 eV at ~6 nm diameter for [111].

Similar band gaps occur at smaller diameters (~3 nm) for [110] nanowires.

Abstract

Structures and electronic properties of rhombohedral [111] and [110] bismuth nanowires are calculated with the use of density functional theory. The formation of an energy band gap from quantum confinement is studied and to improve estimates for the band gap the GW approximation is applied. The [111] oriented nanowires require surface bonds to be chemically saturated to avoid formation of metallic surface states whereas the surface of the [110] nanowires do not support metallic surface states. It is found that the onset of quantum confinement in the surface passivated [111] nanowires occurs at larger critical dimensions than for the [110] nanowires. For the [111] oriented nanowires it is predicted that a band gap of approximately 0.5 eV can be formed at a diameter of approximately 6 nm, whereas for the [110] oriented nanowires a diameter of approximately 3 nm is required to achieve a similar band gap energy. The GW correction is also applied to estimates of the electron affinity, ionisation potentials and work functions for both orientations of the nanowires for various diameters below 5 nm. The magnitude of the energy band gaps that arise in bismuth at critical dimensions of a few nanometers are of the same order as for conventional bulk semiconductors.