The Impact of Electron Phonon Scattering, Finite Size and Lateral Electric Field on Transport Properties of Topological Insulators: A First Principles Quantum Transport Study.

We study, using non-equilibrium Green's function simulations combined with first-principles density functional theory, the edge-state transport in two-dimensional topological insulators. We explore the impact of electron-phonon coupling on carrier transport through the protected states of two widely known topological insulators with different bulk gaps, namely stanene and bismuthene. We observe that the transport in a topological insulator with a small bulk gap (such as stanene) can be heavily affected by electron-phonon scattering, as the bulk states broaden into the bulk gap. In bismuthene with a larger bulk gap, however, a significantly higher immunity to electron-phonon scattering is observed. To mitigate the negative effects of a small bulk gap, finite-size effects are studied in stanene ribbons. The bulk gap increases in ultra-narrow stanene ribbons, but the transport results revealed no improvement in the dissipative case, as the states in the enlarged bulk gaps aren't sufficiently localized. To investigate an application, we also used topological insulator ribbons as a material for field-effect transistors with side gates imposing a lateral electric field. Our results demonstrate that the lateral electric field could offer another avenue to manipulate the edge states and even open a gap in stanene ribbons, leading to an I ON / I OFF of 28 in the ballistic case. These results shed light on the opportunities and challenges in the design of topological insulator field-effect transistors.