Photoconductivity of Single Carbon Nanotubes

TLDR

Infrared laser excitation induces photoconductivity in a single carbon nanotube channel of an ambipolar FET, generating electron–hole pairs that are separated by the source–drain electric field, while asymmetric band alignment or gate coupling produces a photovoltage. The photocurrent exhibits exciton‑energy resonances and peaks for light polarized along the tube, demonstrating that the nanotube FET functions as a sub‑wavelength polarized photodetector with a quantum efficiency exceeding 10%.

Abstract

We observe infrared laser excited photoconductivity from a single carbon nanotube incorporated as the channel of an ambipolar field-effect transistor (FET). Electron−hole pairs are generated within the nanotube molecule, and the carriers are separated by an applied electric field between the source and drain contacts. The photocurrent shows resonances whose energies are in agreement with the energies of exciton states of semiconducting nanotubes of the appropriate diameter. The photocurrent is maximized for photons polarized along the direction of the carbon nanotube. Thus, the nanotube FET acts as a polarized photodetector with a diameter 1000 times smaller than the wavelength of the light it detects and has an estimated quantum efficiency of >10%. A photovoltage is observed when an asymmetric band lineup due to two nonequivalent Schottky barriers or an asymmetric coupling of the gate to the nanotube is present.