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 246

The advantage over the traditionally used indium thin oxide ilms is their
cheaper price, lexibility and resilience to corrosion. For example, a CNT-FET
has been modiied as shown in Fig. 9.2 to induce a sharp discontinuity in
the potential; that is, to produce a drop of energy along the CNT channel.
Electrons that are accelerated at the discontinuity can acquire enough energy
to generate a bright light emitter with a yield that is about 1,000 times higher
than that produced by recombination in a conventional device (Fig. 9.2). 22
The excitation of CNTs can be used to create an eficient EL source. 22-25 At the
same time, monitoring localised EL provides a tool for detecting defects in
CNT devices. In future, additional integration to include optics could lead to a
uniied electronic-optoelectronic technology.

-

SiO 2

Silicon Trench

Figure 9.2 Schematic representation of a CNT as LED. Figure redrawn from Avouris
et al . 11

Unlike many other materials, CNTs have demonstrated very weak
electron-acoustic-phonon coupling and a very large optical phonon energy
of about 200 meV. Excitation of CNTs can be achieved through energetic
(“hot”) carriers lowing through the CNT. The carriers are accelerated by
the applied electric ield, and they gain energy and then lose some of it to
phonons, primarily optical phonons. The energy of the optical phonons is
usually eficiently dissipated into the heat bath provided by the substrate of
the device. However, in the case of suspended nanotubes, evidence for the
existence of a non-equilibrium optical phonon excitation has been reported,
and it seems to degrade the carrier mobility in CNTs. 26,27
Therefore, in a recent article, 28 the authors have investigated the whole
electrical power dissipation in a CNT-based FET. The results from Raman
analysis regarding G band showed both G + and G - transitions clearly resolved.
As the electrical power increases, both G + and G - bands shifted and broadened,
with a trend corresponding to the electric power. Similarly, the corresponding
slopes matched with thermal heating results, although the widths of the bands