First-Principles Electron Transport with Phonon Coupling: Large-Scale at Low Cost

Phonon-assisted tunneling plays a crucial role for electronic device performance and even more so with future size down-scaling. We show how one can include this effect in large-scale first-principles calculations using a single "special thermal displacement" (STD) of the atomic coordinates at almost the same cost as elastic transport calculations. We apply the method to ultra-scaled silicon devices and demonstrate the importance of phonon-assisted band-to-band and source-to-drain tunneling. In a diode the phonons lead to a rectification ratio suppression in good agreement with experiments, while in an ultra-thin body transistor the phonons increase off-currents by four orders of magnitude, and the subthreshold swing by a factor of four, in agreement with perturbation theory.