Role of Single Defects in Electronic Transport through Carbon Nanotube Field-Effect Transistors

TL;DR

This study investigates how individual defects affect electron transport in carbon nanotube transistors using advanced microscopy techniques, revealing localized defect effects and their impact on device conductance.

Contribution

It introduces combined scanning gate and impedance microscopy to quantify defect potentials and their influence on transport in CNFETs, providing new insights into defect-related conduction mechanisms.

Findings

Defects cause localized potential variations in CNFETs.

Transport is diffusive when the device is 'on' and affected by defects when 'off'.

High-resolution imaging of weak defects is demonstrated.

Abstract

The influence of defects on electron transport in single-wall carbon nanotube field effect transistors (CNFETs) is probed by combined scanning gate microscopy (SGM) and scanning impedance microscopy (SIM). SGM reveals a localized field effect at discrete defects along the CNFET length. The depletion surface potential of individual defects is quantified from the SGM-imaged radius of the defect as a function of tip bias voltage. This provides a measure of the Fermi level at the defect with zero tip voltage, which is as small as 20 meV for the strongest defects. The effect of defects on transport is probed by SIM as a function of backgate and tip-gate voltage. When the backgate voltage is set so the CNFET is "on" (conducting), SIM reveals a uniform potential drop along its length, consistent with diffusive transport. In contrast, when the CNFET is "off", potential steps develop at the position of depleted defects. Finally, high-resolution imaging of a second set of weak defects is achieved in a new "tip-gated" SIM mode.