As discussed in Section 5.5.2, high energy phonons such as
and
-point phonons reduce the on-current only weakly, but can
increase the gate-delay time considerably due to charge pileup in the
channel. Low energy phonons such as the RBM phonon can reduce the on-current
more effectively, but have a weaker effect on the gate-delay time. However, due
to strong coupling, scattering processes are mostly due to electron-phonon
interaction with high energy phonons. Therefore, the on-current of short
CNT-FETs can be close to the ballistic limit [279] (see Fig. 5.26),
whereas the gate-delay time can be significantly below that
limit [280,89]. The intrinsic (without
parasitic capacitances) gate-delay time for the
ballistic case can be approximated as
, or equivalently
[281]. The highest reported cutoff frequency for a device with a
length of less than
is
[90], which is far below the
ballistic limit. Apart from parasitic capacitances, inelastic electron-phonon
interaction with high energy phonon has to be considered to explain the
results.
![]() ![]() |
M. Pourfath: Numerical Study of Quantum Transport in Carbon Nanotube-Based Transistors