Photo-gating Carbon Nanotube Transistors

TL;DR

This paper demonstrates that in carbon nanotube transistors, visible light absorption in the silicon substrate creates a photovoltage that acts as an electrical gate, dominating the photocurrent response over direct electron-hole pair generation.

Contribution

It reveals that photogating, induced by substrate photovoltage, is the primary mechanism affecting photocurrent in nanotube transistors under visible light.

Findings

Photovoltage from silicon substrate significantly influences nanotube transistor photocurrent.

Photocurrent shows strong non-linear power dependence.

Photocurrent can be detected even when illumination is 1 mm away from the nanotube.

Abstract

Optoelectronic measurements of carbon nanotube transistors have shown a wide variety of sensitivites to the incident light. Direct photocurrent processes compete with a number of extrinsic mechanisms. Here we show that visible light absorption in the silicon substrate generates a photovoltage that can electrically gate the nanotube device. The photocurrent induced by the changing gate voltage can be significantly larger than that due to direct electron-hole pair generation in the nanotube. The dominance of photogating in these devices is confirmed by the power and position dependence of the resulting photocurrent. The power dependence is strongly non-linear and photocurrents are measured through the device even when the laser illuminates up to 1~mm from the nanotube.