Nonequilibrium Green's Function Treatment of Phonon Scattering in Carbon-Nanotube Transistors

S.O Koswatta,D.E Nikonov,S Hasan,M.S Lundstrom,M.P Anantram

doi:10.1109/ted.2007.902900

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.

Highlights

S INCE THE first demonstration of carbon-nanotube (CNT) field-effect transistors in 1998 [1], [2], there has been tremendous progress in their performance and physical understanding [3]
We first study the effects of phonon scattering on the carbon-nanotube field-effect transistors (CNTFETs) characteristics using a (16,0) tube as a representative case
For the simulation of acoustic phonons (APs) scattering, a heavy-doped extension region is used for better convergence of the electrostatic solution

Summary

Introduction

S INCE THE first demonstration of carbon-nanotube (CNT) field-effect transistors in 1998 [1], [2], there has been tremendous progress in their performance and physical understanding [3]. Both electronic and optoelectronic devices based on CNTs have been realized, and the fabrication processes have been optimized. Ballistic transport in CNTs has been experimentally demonstrated for low-bias conditions at low temperatures [4], [5]. Manuscript received January 3, 2007; revised May 29, 2007.

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