Atomistic full-band simulations of silicon nanowire transistors: Effects of electron-phonon scattering

An atomistic full-band quantum transport simulator has been developed to study three-dimensional Si nanowire field-effect transistors in the presence of electron-phonon scattering. The nonequilibrium Green’s function (NEGF) formalism is solved in a nearest-neighbor sp3d5s* tight-binding basis. The scattering self-energies are derived in the self-consistent Born approximation to inelastically couple the full electron and phonon energy spectra. The band dispersion and the eigenmodes of the confined phonons are calculated using a dynamical matrix that includes the bond and the angle deformations of the nanowires. The optimization of the numerical algorithms and the parallelization of the NEGF scheme enable the investigation of nanowire structures with diameters up to 3 nm and lengths over 40 nm. It is found that the reduction in the device drain current, caused by electron-phonon scattering, is more important in the ON state than in the OFF state of the transistor. Ballistic transport simulations considerably overestimate the device ON currents by artificially increasing the charge injection mechanism at the source contact.