Scaling analysis of electron transport through metal-semiconducting carbon nanotube interfaces: Evolution from the molecular limit to the bulk limit

TL;DR

This paper investigates how electron transport in metal-semiconducting carbon nanotube interfaces varies with nanotube length, revealing a transition from tunneling to thermally activated conduction and emphasizing the importance of atomic-scale and electrostatic effects.

Contribution

It provides a detailed scaling analysis of electron transport considering atomic structure and electrostatics, offering new insights into Schottky barrier formation and conductance behavior in nanotube devices.

Findings

Transition from tunneling to thermal activation with increasing nanotube length

Weaker temperature dependence compared to planar interfaces

Conductance sensitive to potential response models

Abstract

We present a scaling analysis of electronic and transport properties of metal-semiconducting carbon nanotube interfaces as a function of the nanotube length within the coherent transport regime, which takes fully into account atomic-scale electronic structure and three-dimensional electrostatics of the metal-nanotube interface using a real-space Green's function based self-consistent tight-binding theory. As the first example, we examine devices formed by attaching finite-size single-wall carbon nanotubes (SWNT) to both high- and low- work function metallic electrodes through the dangling bonds at the end. We analyze the nature of Schottky barrier formation at the metal-nanotube interface by examining the electrostatics, the band lineup and the conductance of the metal-SWNT molecule-metal junction as a function of the SWNT molecule length and metal-SWNT coupling strength. We show that the confined cylindrical geometry and the atomistic nature of electronic processes across the metal-SWNT interface leads to a different physical picture of band alignment from that of the planar metal-semiconductor interface. We analyze the temperature and length dependence of the conductance of the SWNT junctions, which shows a transition from tunneling- to thermal activation-dominated transport with increasing nanotube length. The temperature dependence of the conductance is much weaker than that of the planar metal-semiconductor interface due to the finite number of conduction channels within the SWNT junctions. We find that the current-voltage characteristics of the metal-SWNT molecule-metal junctions are sensitive to models of the potential response to the applied source/drain bias voltages.