Atomistic simulation of nanowires in the sp3d5s* tight-binding formalism:: From boundary conditions to strain calculations

As the active dimensions of metal-oxide field-effect transistors are approaching the atomic scale, the electronic properties of these nanowire devices must be treated on a quantum mechanical level. In this paper, the transmission coefficients and the density of states of biased and unbiased Si and GaAs nanowires are simulated using the sp(3)d(5)s(*) empirical tight-binding method. Each atom, as well as the connections to its nearest neighbors, is represented explicitly. The material parameters are optimized to reproduce bulk band-structure characteristics in various crystal directions and various strain conditions. A scattering boundary method to calculate the open boundary conditions in nanowire transistors is developed to reduce the computational burden. Existing methods such as iterative or generalized eigenvalue problem approaches are significantly more expensive than the transport simulation through the device. The algorithm can be coupled to nonequilibrium Green's function and wave function transport calculations. The speed improvement is even larger if the wire transport direction is different from [100]. Finally, it is demonstrated that strain effects can be easily included in the present nanowire simulations.