CNT infrared detectors using Schottky barriers and p-n junctions based FETs

Carbon nanotube (CNT) Schottky barriers and p-n junctions based photovoltaic photodiodes have been demonstrated they were able to detect infrared (IR) signals. However, how to optimize the performances of these one dimensional (1D) detectors is not clear due to the variation of the properties of as-made CNTs. We investigated the photocurrent variation by modulating the depletion regions through electrostatic doping from a gate of the CNT field effect transistor (FET). It showed that the photocurrent from the Schottky diodes between Au and CNT can be maximized by applying a moderate negative gate voltage, indicating widest depletion width in that state. By introducing a small Aluminum gate underneath and partially couple to a CNT, two inversely connecting p-n junctions will be formed with an appropriate positive gate voltage. As a result, dark current was suppressed around 3 orders and photocurrent was enhanced, resulting in a high on/off ratio photocurrent and a ~0.1 V open circuit voltage. The experiment results show that electrostatic doping using CNTFETs can improve the performances of the 1D photodiodes. The CNTFET based IR detector may have substantial potential for further nano-optoelectronics.

I. INTRODUCTION

Carbon nanotube (CNT) is a novel one dimensional (1D) material that has been widely explored in nano-electronics and optoelectronics due to its outstanding physical and electrical properties. Single wall CNTs (SWCNT) is constructed from wrapping a graphene sheet into a seamless tube. They can be either metallic or semiconductor depending on the chiralities of the CNTs. Semiconductor CNT is a direct band gap material and the band gap can be tuned by engineering its diameter [1], making it an excellent material for nano-photodetectors with selective wavelength. In addition, its long ballistic transport length can reduce the dark current due to the suppressed phonon electron scattering [2].