Near-infrared photodetection using random networks of single-walled carbon nanotubes with asymmetrical work-function electrodes

Abstract

We investigate the use of random networks of single-walled carbon nanotubes for near-infrared photodetection. By increasing the number of nanotubes between asymmetrical work-function electrodes using dielectrophoretic assembly, the effect of Fermi-level pinning of nanotube-Schottky contacts was revealed in the linear current-voltage characteristic. The extracted device resistance showed an abrupt drop when the numerous intertube junctions formed densely packed networks in the electrode channel. Under the excitation of a near-infrared laser, we performed the photocurrent measurement at ambient temperature at different light powers. Our devices with densely packed nanotube networks showed enhanced photoconductive detection of responsivity, detectivity, and detection response. This is attributed to the increase in the photoabsorption area, the decrease of the channel resistance, and the formation of continuous conducting paths for high-efficient charge percolation. The photoconductive responsivity of up to 8.0 μA W-1 was found with a detectivity of about 4.9 × 105 cm Hz1/2 W-1, which is 4 orders of magnitude greater than that achieved in the channel with individual nanotubes deposited and comparable to that of suspended nanotube bolometers. The densely packed nanotube devices had a detection response of ∼ 4 ms under a finite bias that can be explained by the short-diffusion length of the photoexcited electrons and holes. However, the decrease in the photocurrent with time observed in our devices that exhibited photovoltaic characteristics indicates that electron-hole pair recombination in the nanotube networks occurs with differing characteristic time scales of the injected electrons and holes.