Zener tunneling in the electrical transport of quasi-metallic carbon nanotubes

TL;DR

This paper theoretically investigates how Zener tunneling influences electrical transport in quasi-metallic carbon nanotubes, especially considering defect scattering, revealing that Zener tunneling can occur at realistic electric fields and is enhanced by defects.

Contribution

It introduces a quantum mechanical model that accounts for Zener tunneling, defect scattering, and phonon interactions to analyze transport in quasi-metallic nanotubes, highlighting defect effects.

Findings

Zener tunneling enables current flow even in the forbidden gap.

Defects lower the electric field threshold for Zener tunneling.

Zener tunneling significantly impacts the current-voltage behavior in low-quality samples.

Abstract

We study theoretically the impact of Zener tunneling on the charge-transport properties of quasi-metallic (Qm) carbon nanotubes (characterized by forbidden band gaps of few tens of meV). We also analyze the interplay between Zener tunneling and elastic scattering on defects. To this purpose we use a model based on the master equation for the density matrix, that takes into account the inter-band Zener transitions induced by the electric field (a quantum mechanical effect), the electron-defect scattering and the electron-phonon scattering. In presence of Zener tunnelling the Qm tubes support an electrical current even when the Fermi energy lies in the forbidden band gap. In absence of elastic scattering (in high quality samples), the small size of the band gap of Qm tubes enables Zener tunnelling for realistic values of the the electric field (above $\sim$ 1 V/\mu m). The presence of a strong elastic scattering (in low quality samples) further decreases the values of the field required to observe Zener tunnelling. Indeed, for elastic-scattering lengths of the order of 50 nm, Zener tunnelling affects the current/voltage characteristic already in the linear regime. In other words, in quasi-metallic tubes, Zener tunneling is made more visible by defects.