Schottky-to-Ohmic Crossover in Carbon Nanotube Transistor Contacts

TL;DR

This paper investigates the transition from Schottky to ohmic contacts in carbon nanotube transistors, revealing a near-crossover behavior in high-performance devices and highlighting the significant role of tunneling effects.

Contribution

It provides a detailed calculation of device characteristics showing the crossover behavior and the importance of tunneling in the contact regime.

Findings

High-performance devices are close to the Schottky-Ohmic crossover.

Tunneling significantly influences current behavior even near the crossover.

Current saturation is affected by tunneling, contrary to expectations.

Abstract

For carbon nanotube transistors, as for graphene, the electrical contacts are a key factor limiting device performance. We calculate the device characteristics as a function of nanotube diameter and metal workfunction. Although the on-state current varies continuously, the transfer characteristics reveal a relatively abrupt crossover from Schottky to ohmic contacts. We find that typical high-performance devices fall surprisingly close to the crossover. Surprisingly, tunneling plays an important role even in this regime, so that current fails to saturate with gate voltage as was expected due to "source exhaustion".