Effect of scattering and contacts on current and electrostatics in carbon nanotubes

TL;DR

This study uses computational methods to analyze how scattering, contacts, length, and diameter influence the electrostatic potential and current in carbon nanotubes, revealing a transition from ballistic to diffusive transport regimes.

Contribution

It introduces a self-consistent computational approach including electron-phonon scattering to understand transport and electrostatics in carbon nanotubes, highlighting effects of geometry and contacts.

Findings

Potential profiles change with bias and diameter.

Differential conductance varies with nanotube parameters.

Current capacity increases with diameter.

Abstract

We computationally study the electrostatic potential profile and current carrying capacity of carbon nanotubes as a function of length and diameter. Our study is based on solving the non equilibrium Green's function and Poisson equations self-consistently, including the effect of electron-phonon scattering. A transition from ballistic to diffusive regime of electron transport with increase of applied bias is manifested by qualitative changes in potential profiles, differential conductance and electric field in a nanotube. In the low bias ballistic limit, most of the applied voltage drop occurs near the contacts. In addition, the electric field at the tube center increases proportionally with diameter. In contrast, at high biases, most of the applied voltage drops across the nanotube, and the electric field at the tube center decreases with increase in diameter. We find that the differential conductance can increase or decrease with bias as a result of an interplay of nanotube length, diameter and a quality factor of the contacts. From an application view point, we find that the current carrying capacity of nanotubes increases with increase in diameter. Finally, we investigate the role of inner tubes in affecting the current carried by the outermost tube of a multiwalled nanotube.