Carrier transport in two-dimensional topological insulator nanoribbons in the presence of vacancy defects

Sabyasachi Tiwari,Maarten L Van De Put,William G Vandenberghe,Bart Sorée

doi:10.1088/2053-1583/ab0058

Sabyasachi Tiwari, Maarten L Van De Put + Show 2 more

Open Access

https://doi.org/10.1088/2053-1583/ab0058

Copy DOI

Abstract

Using the non-equilibrium Green’s function formalism, we study carrier transport through imperfect two-dimensional (2D) topological insulator (TI) ribbons. In particular, we investigate the effect of vacancy defects on the carrier transport in 2D TI ribbons with hexagonal lattice structure. To account for the random distribution of the vacancy defects, we present a statistical study of varying defect densities by stochastically sampling different defect configurations. We demonstrate that the topological edge states of TI ribbons are fairly robust against a high concentration (up to 2%) of defects. At very high defect densities, we observe an increased inter-edge interaction, mediated by the localisation of the edge states within the bulk region. This effect causes significant back-scattering of the, otherwise protected, edge-states at very high defect concentrations (>2%), resulting in a loss of conduction through the TI ribbon. We discuss how this coherent vacancy scattering can be used to our advantage for the development of TI-based transistors. We find that there is an optimal concentration of vacancies yielding an ON–OFF current ratio of up to two orders of magnitude. Finally, we investigate the importance of spin–orbit coupling on the robustness of the edge states in the TI ribbon and show that increased spin–orbit coupling could further increase the ON–OFF ratio.

Highlights

Continued scaling has deteriorated the mobility of electronic devices based on three-dimensional (3D) materials [1, 2], resulting in an increasing interest in two-dimensional (2D) materials [3, 4]
We have investigated electronic transport in 2D topological insulator (TI) ribbons with a hexagonal lattice structure and zigzag edge orientation using the Kane–Mele Hamiltonian
Our results were obtained for TI ribbons with realistic parameters, obtained by fitting our model to the density functional theory (DFT) bandstructure of bulk stanene

Summary

Introduction

Continued scaling has deteriorated the mobility of electronic devices based on three-dimensional (3D) materials [1, 2], resulting in an increasing interest in two-dimensional (2D) materials [3, 4]. The intrinsic 2D structure of these materials offers a great avenue for optimum electrostatic control with sufficient mobility for carrier transport in scaled electronic devices [1]. One avenue of research focuses on improving material growth and device fabrication techniques. An alternative avenue, which we will pursue in this paper, is to develop materials and device systems where carrier transport is robust against imperfections. We want to exploit topological protection, i.e. robustness against small perturbations, of certain materials properties, while maintaining excellent 2D material electrostatic control. Materials that offer such prospects are 2D topological insulators (TIs) [16]

Methods

Results

Conclusion