Atomistic modeling of coupled electron-phonon transport in nanowire transistors

Abstract

Self-heating effects are investigated in ultrascaled gate-all-around silicon nanowire field-effect transistors (NWFETs) using a full-band and atomistic quantum transport simulator where electron and phonon transport are fully coupled. The nonequilibrium Green's function formalism is used for that purpose, within a nearest-neighbor sp 3 d 5 s * tight-binding basis for electrons and a modified valence-force-field model for phonons. Electron-phonon and phonon-electron interactions are taken into account through specific scattering self-energies treated in the self-consistent Born approximation. The electron and phonon systems are driven out of equilibrium; energy is exchanged between them while the total energy current remains conserved. This gives rise to local variations of the lattice temperature and the formation of hot spots. The resulting self-heating effects strongly increase the electron-phonon scattering strength and lead to a significant reduction of the ON-current in the considered ultrascaled Si NWFET with a diameter of 3 nm and a length of 45 nm. At the same time, the lattice temperature exhibits a maximum close to the drain contact of the transistor.

Electron-phonon scattering from Green's function transport combined with molecular dynamics: Applications to mobility predictions

“…For device calculations, inclusion of EPC leads to a very substantial complication of the calculations, when treated with NEGF [10,12,14]. The MD-Landauer method could, on the other hand, be included in device calculations without significant extra computational load.…”

“…However, the resulting equations are numerically very challenging and approximations need to be applied. Approximate methods include lowest order expansions of the inelastic current [12,13] or approximations to the EPC self-energy [10,14].…”

Hypergeometric resummation of self-consistent sunset diagrams for steady-state electron-boson quantum many-body systems out of equilibrium

“…On the other hand, accounting for all the relevant quantum manybody interactions for such systems composed of thousands of atoms is computationally prohibitively expensive. 12,13 For example, simulation of photocurrent in a photovoltaic cell requires to take into account electronic structure of the cell, electron-photon interactions responsible for photoexcitation, by electron-hole recombination processes, emission and absorption of phonons and scattering by disorder.…”

Introduction

“…For instance, it has been shown theoretically that electron-phonon scattering drastically influences the current characteristics in ultimate nanowire transistors [1]. The miniaturization tends to enhance also the impact of thermal effects, and accurate description of phonon scattering at the nanoscale is becoming crucial to understand and manage thermal dissipation in devices and circuits [2]. In modern optoelectronic devices like new generation solar cells, it is also essential to consider appropriate models of light-matter interaction at the microscopic level [3,4].…”