Effect of vacancy defects on the carrier transport of a two-dimensional Topological Insulator Field effect Transistor

As scaling reduces field-effect transistor (FET) channel length, optimal electrostatic control can be maintained by using two-dimensional (2D) materials as the channel material. However, 2D materials are marred with a high level of defects, which negatively affects their carrier transport properties. Interestingly, 2D topological insulators (TIs) are shown to be immune to imperfections as the topological edge states are protected by time reversal symmetry. However, a better understanding of the effect of the vacancy defects on the ballistic transport properties of the 2D topological insulators is necessary. We present a theoretical study of the effect of vacancy defects using a 2D Non-Equilibrium Green’s function (NEGF) based formulation with a Bernevig-Hughes-Zhang type tight-binding Hamiltonian, including spin-orbit interaction. We account for the open nature of the system by introducing appropriate contact self-energy terms using quantum transmitting boundary conditions. We analyze the ballistic transport characteristics of various TI-FETs and identify the topological edge symmetry breaking limit as a function of both position and amount of vacancy defects compared to the pristine TI lattice.