OVERVIEW ON THE MAJOR RESEARCH ACTIVITIES ON CARBON NANOTUBES BEING DONE IN AMERICA, EUROPE AND ASIA - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 245

Gate

Source

Drain

CNT

insulator

SiO 2

Siliconwafer(p++)

Figure 9.1 Schematic representation of a FET. Figure redrawn from Avouris et al . 11

In the case of CNT-based FETs, the role of the channel is played by one
or more semiconducting nanotubes. The irst CNT-FETs were reported in
1998. 16,17 The key advantage is the low scattering in the CNT and the high
mobility of the FET channel. In addition, as reported before, there are two
contributions to the capacitance, C G and C Q , and in conventional devices, C G <
C Q , while in CNT-FETs C G ≈ C Q .
Therefore, in a conventional FET the ability of the gate to control the
potential in the channel is limited once V g exceeds the threshold voltage,
V th . 18 As a consequence, increasing the gate voltage above this value does not
change the bands anymore. Conversely, in a CNT-FET the gate can still retain
control of the potential, thus contributing to the current. 19 In general, the main
advantages of CNT-FETs over conventional systems are their much lower
capacitance and their lower operating voltage. Furthermore, the small size
of the CNTs allows for the fabrication of aligned arrays with a high packing
density. However, careful design and engineering are needed to make sure
that the system is eficient.
In an electronic device, energy can be released as heat (phonons), and
a small fraction may involve the emission of a photon. This light emission
process is called electroluminescence (EL) and is extensively used to produce
solid-state light sources such as light emitting diodes (LEDs). Although the
mechanism of this emission is similar to that of a LED, in CNTs the light does
not originate from a ixed point along the tube, but its origin can be translated
by simply changing V g . As a consequence, more intense and brighter light
sources can be produced with CNTs. Some properties of single-walled CNT
(SWCNT) ilms, including their conductivity, their optical transparency and
their lexibility, render them ideal anodes for organic LEDs (OLED S ). 20,21