Non-equilibrium Green's function treatment of phonon scattering in carbon nanotube transistors

TL;DR

This paper models phonon scattering effects in carbon nanotube transistors using non-equilibrium Green's functions, revealing bias-dependent impacts on device performance and the influence of different phonon modes.

Contribution

It provides a detailed quantum transport simulation framework incorporating realistic phonon dispersion and electron-phonon interactions for CNTFETs.

Findings

Phonon scattering effects depend on bias voltage and phonon type.

High-energy optical phonon scattering dominates at large biases.

Diameter influences scattering effects, except for RBM modes.

Abstract

We present the detailed treatment of dissipative quantum transport in carbon nanotube field-effect transistors (CNTFETs) using the non-equilibrium Green's function formalism. The effect of phonon scattering on the device characteristics of CNTFETs is explored using extensive numerical simulation. Both intra-valley and inter-valley scattering mediated by acoustic (AP), optical (OP), and radial breathing mode (RBM) phonons are treated. Realistic phonon dispersion calculations are performed using force-constant methods, and electron-phonon coupling is determined through microscopic theory. Specific simulation results are presented for (16,0), (19,0), and (22,0) zigzag CNTFETs that are in the experimentally useful diameter range. We find that the effect of phonon scattering on device performance has a distinct bias dependence. Up to moderate gate biases the influence of high-energy OP scattering is suppressed, and the device current is reduced due to elastic back-scattering by AP and low-energy RBM phonons. At large gate biases the current degradation is mainly due to high-energy OP scattering. The influence of both AP and high-energy OP scattering is reduced for larger diameter tubes. The effect of RBM mode, however, is nearly independent of the diameter for the tubes studied here.