Full Quantum Investigation of Low Field Mobility in Short-Channel Silicon Nanowire FETS

Abstract

A computational study on short-channel Silicon- nanowire-FETs is proposed by means of a 3-D full-quantum treatment within the coupled mode space non-equilibrium Green's function formalism. Electron-phonon interaction and surface roughness are considered as limiting scattering mech- anisms. The dependence of the effective mobility on the channel length is addressed showing the importance of quantum-phase- coherence in ultra-scaled devices and analyzing the impact of the different scattering mechanisms. The scaling trends for the back-scattering coefficient is also investigated. I. INTRODUCTION Recently, both experimental and theoretical studies have been devoted to investigate the mobility reduction in short- channel devices, showing that it is probably due to the effect of ballistic electrons and the increasing importance of many other sources of scattering like thickness fluctuations, surface roughness (SR) at the Si-SiO2 interface, doping pockets and random impurities (1)-(11). As device dimensions are further scaled and a quasi-ballistic regime is achieved, a full-quantum transport simulation is envisaged to correctly describe the ballistic component of the current and the elastic scattering mechanisms which are ruled by quantum-phase-coherence. In this work we present a com- putational study on short-channel Silicon-nanowire (SiNW) FETs based on a self-consistent 3-D full-quantum treatment via the coupled mode-space (CMS) non equilibrium Green's function (NEGF) method (8), (9) and the Keldysh formalism in the parabolic effective-mass approximation. We address elastic scattering due to surface roughness via a microscopic description of potential fluctuations at the Si/SiO2 interface (10) and inelastic electron-phonon (PH) scattering via the self- consistent Born approximation. The dependence of the effec- tive mobility on the channel length is investigated showing the importance of quantum-phase-coherence in ultra-scaled devices and analyzing the impact of the different scattering mechanisms. Finally, we discuss the scaling trend for the back- scattering coefficient.