Carbon Nanotube Field-Effect Transistor-Based Photodetectors

Abstract

This chapter discusses the five types of CNT field-effect transistors CNTFETs to investigate and improve the performance of CNT-based IR detectors. In the Au-CNT-Au CNTFET back-gate, the detector performance is improved by applying voltages to the back-gate, resulting in smaller dark current and higher Iphoto. Back-gate is capacitative-coupled to the CNT, and thus, application of Vg can electrostatically modulate the Fermi energy of CNT so as to control the Schottky barriers that are responsible for Iphoto generation. The Ag-CNT-Ag CNTFET back-gate produces higher Voc under IR illumination, since the built-in potential between Ag and CNT is higher than that of Au and CNT, showing the significance of metal workfunction. The two CNTFETs have symmetric metal structures, that constrain the performance of the detectors, because separated electrons and holes from one Schottky barrier need to tunnel through another barrier. In the Au-CNT-Ag CNTFET back-gate, an asymmetric metal structure is used, and both Iphoto and Voc are highly improved. The reason is that the electrons and holes from the Ag-CNT interface only needed to pass through a small barrier between Au and CNT before being collected. CNTFET with back-gate structure is easy to fabricate and provide valuable information for improving detector performance. However, the back-gate structure is not suitable for larger scale detector arrays, because the back-gate will modulate all detectors simultaneously. A middle-gate CNTFET was fabricated in order to control each detector independently. But a CNT detector with middle-gate structure and symmetric metal structure cannot deliver optimal performance. In order to find the optimal detector design, an asymmetric multigate CNTFET is introduced, with asymmetric metal structure and multiple gates, including back-gate, gates for source and drain, and middle gates. © 2012 Elsevier Inc. All rights reserved.