TABLE OF CONTENTS Single walled carbon nanotubes were discovered in 1993 [5.6], and only a few years later carbon nanotube field-effect transistors (CNTFETs) [5.1, 5.2, 5.3] and circuits [5.10, 5.11] were realized. The science and technology of CNTFETs is still at an early stage, but they do show promise. They also provide an opportunity to apply the theory of ballistic transistors to an interesting new materials system. At this stage, it is hard to predict the future of carbon nanotube electronics, but working on CNTFETs provides a concrete context in which to learn how to treat electronic devices at the molecular scale. The issues relating to contact, interfaces, transport, etc. that must be addressed for CNTFETs are likely to be important for other types of devices as well.
Before we discuss CNTFETs, it is important to realize that there are two different ways to make a transistor. As shown in Fig. 5.18a, the first type is a MOSFET-like device for which any charge demanded by the gate is supplied from the contacts. We refer to such a device as a charge-modulation transistor. The second type of transistor is shown in Fig. 5.18b. In this case, there is a barrier at the contact, and the transistor operates by modulating the width of the tunnel barrier and, therefore, the current that flows in from the contact. We refer to this type of device as a transmission-modulation transistor. It is also known as a Schottky barrier transistor and, although it is an...
