5. Atomistic Simulations of Tunneling FETs

With continuous scaling of semiconductor devices, the number of atoms in transistors becomes countable. Various effects related to the device atomic structure, such as random dopants, edge roughness, and channel-oxide interface, have great impact on device performance. Therefore, it is valuable to study material electronic properties and device transport characteristics at the atomic level. In this chapter, we review the atomistic modeling methods of density functional theory (DFT) and tight-binding (TB) model within the Keldysh non-equilibrium Green’s function (NEGF) framework. To investigate impurity scattering in devices, the framework of non-equilibrium vertex correction (NVC) with NEGF–DFT is reviewed. The NEGF–DFT–NVC approach can give the statistic transport information of nanodevices with atomic disorder and is applied to study disorder effects in graphene TFETs. Due to the diffusive impurity scattering, the band-to-band tunneling current is substantially reduced in graphene TFETs with atomic disorder. At last, atomistic simulations of monolayer transition metal dichalcogenide (TMDC) TFETs are carried out by using the NEGF–TB method. It is revealed that the orientation-dependent transport is determined by conduction sub-bands and the atomic structure along the transport direction.