Atomistic simulation of electron and phonon transport in nano-devices

In this paper, the electrical, thermal, and coupled electro-thermal properties of silicon nanowire field-effect transistors (NWFETs) are investigated through advanced numerical simulations. An atomistic quantum transport solver based on the Non-equilibrium Green´s Function (NEGF) formalism is utilized as modeling tool. The electron characteristics are treated within an empirical tight-binding basis, while a modified valence-force-field method is used to describe phonons. Device simulations going beyond the ballistic limit of transport are performed: electron-phonon interactions with an equilibrium and out-of-equilibrium phonon population are considered as well as an-harmonic phonon-phonon scattering. It is found that ultrascaled Si NWFETs with a gate length of 15 nm operate at about 50% of their ballistic limit. This poor performance can be explained by large self-heating effects that drastically increase the lattice temperature and thus reduce the drain current.