A Doping‐Free Carbon Nanotube CMOS Inverter‐Based Bipolar Diode and Ambipolar Transistor

Abstract

Single-walled carbon nanotubes (SWCNTs) have been extensively studied since they were discovered by Iijima in 1991, and in particular many SWCNT-based electrical devices have been fabricated and evaluated. These devices include field-effect transistors (FETs) and diodes. When contacted with Pd and Sc, it has been shown that carriers can be injected, barrier-free, into the valence band (p-FET) and conduction band (n-FET), respectively, forming the basis for doping-free carbon nanotube (CNT)based ballistic complementary metal-oxide semiconductor (CMOS) technology. Similar to Si-based CMOS, the CNT-based CMOS inverter (Fig. 1a) forms the simplest and most fundamental unit for more complex CMOS circuits. In this Communication we show, in addition to the usual CMOS inverter functions, that this basic device unit can also be readily configured to function as an effective ambipolar FET and a new type of diode: the barrier-free bipolar diode. Several CNT-based diodes have been developed. These include p–n junction diodes formed by chemical doping and split gates, and Schottky diodes based on intramolecular junctions and metal–CNT junctions. While the functioning of the p-n junction diode relies on the diffusion of minority carriers in the device, which limits its high-speed applications, the presence of the Schottky barrier (SB) in the Schottky diode significantly reduces the maximum current that may be achieved. In general, the conventional diode may