Optoelectronics with Carbon Nanotubes

Chapter I Introduction
It is well recognized that the ongoing scaling down of electronic technology, especially
with silicon, cannot continue forever because of its theoretical and technological limits 1 .
Alternative device technologies are needed to enhance or replace the current approach. Carbon
nanotubes (CNTs), since their discovery in 1991 2 , followed by the discovery of single-walled
carbon nanotubes (SWNTs) in 1993 3 by Iijima, have been a subject of intense research because
of the many unique and desirable properties they exhibit, such as their extraordinary tensile
strength, the ability to withstand high pH and temperature, and particularly, their distinctive
electronic and optical properties 4-6 . Multiwall carbon nanotubes (MWNTs) are concentric tubes
of rolled up one-atom layer sheet in a honeycomb configuration of carbon atoms (i.e. graphene),
while SWNTs are composed of only one such tube. The diameter of a CNT can be sub-
nanometer for SWNTs, up to a few to tens of nanometers. Detailed physical characteristics of
these structures are covered in the next section.
The SWNT with its simpler structure has garnered a greater interest in electronics; it can
be a semiconductor or a metal with very high mobility that can withstand enormous current
densities. This makes it attractive for use in nano-scale electronics, as the sizes of integrated
circuits become ever smaller and are reaching the natural limit of miniaturization. Currently, as
silicon devices are made smaller and denser, problems with leakage through dielectric and heat
dissipation are two major obstacles to the further scaling down in existing chip designs. The
superior mobility of SWNTs means less phonon scattering (i.e., less heat production per unit
current), and their extremely small sizes are naturally advantageous in micro- and nano-scale
electronics. Field-effect transistors made from CNTs (CNTFETs) were demonstrated as early as
1998 by Tans et al. and Martel et al. 7, 8 . Compared to conventional bulk silicon MOSFET,
CNTFET exhibits superior performance in terms of transconductance and drive currents by a
factor of a few per unit width, making it an attractive alternative to silicon 9 . In addition, as will
be discussed shortly, their reduced dimensionality contributes to their unique electrical and
optical properties, which make them a promising candidate for near- to mid-infrared
optoelectronics.
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