ON-State Current Paths and OFF-State Leakage in Nanoscale Silicene Field-Effect Transistors

Topological insulators are promising candidates for dissipationless electronics and spintronics. For the design and application of small-sized topological transistors, it is vital to suppress the OFF-state leakage and keep utilizing the edge or surface states to carry the ON-state current. Using the nonequilibrium Green's function method, the transport properties of clean and disordered silicene were studied in the nanoscale regime. The results revealed the following. (1) The low-energy electron transport across the scattering region included two types of paths, namely, helical edge states and interstate tunnels. The choice of electrons for the two transmission paths was related to the length of the scattering region. When there was a band gap in the ky direction, electrons tended to tunnel between armchair-edge states along the x axis. It was only when the length met Nx = 3n + 1 that the electrons mainly propagated through the helical edge states. (2) The weak electric field could significantly enhance the wave-function overlap between armchair-edge states and can be used to switch electron-transport paths. (3) The origin of the leakage current in the nanoscale transistors was interstate quantum tunneling; this was promoted-instead of suppressed-by weak or strong disorders. (4) The effect of a strong electric field on the electron transport was opposite to that of the weak field. After reaching a critical value of & lambda;E > 2 & lambda;SO, the vertical electric field decreased the interstate tunneling probability and increasing the staggered potential was an effective method to suppress the OFF-state leakage.