Photo-thermal Self-oscillations in Cavity-Coupled Carbon Nanotube pn-Devices

TL;DR

This paper reports the discovery of photothermal self-oscillations in suspended carbon nanotube pn devices caused by optical heating and thermal contraction, with oscillations detected via tunneling current changes.

Contribution

It demonstrates the first observation of photothermal self-oscillations in CNT pn devices and models the phenomenon using a temperature-dependent Zener tunneling approach.

Findings

Oscillations caused by optical heating and thermal contraction.

Good agreement between the Zener tunneling model and experimental data.

Oscillations detectable through tunneling current variations.

Abstract

We observe photothermal self-oscillations in individual, suspended, quasi-metallic carbon nanotube (CNT) pn devices irradiated with focused CW 633nm light. Here, the bottom of the trench forms an optical cavity with an anti-node at lambda/4. Oscillations arise from the optical heating of the nanotube, which causes thermal contraction of the nanotube (negative thermal expansion coefficient). This, in turn, moves the CNT out of the anti-node (maximum field intensity), where the nanotube cools to a lower temperature. It then expands and returns to the maximum field intensity anti-node where it is optically heated once again. The oscillations are observed through a change of the tunneling current in the CNT device. A pn-junction, established by two electrostatic gates positioned beneath the nanotube, results in Zener tunneling, which depends strongly on temperature. A Zener tunneling model with oscillating temperature shows good agreement with our measured I-V curves, providing further evidence that these oscillations are photothermal in nature.