  We investigate theoretically the feasibility of generation and amplification
of terahertz radiation in aligned achiral carbon nanotubes (zigzag and
armchair) in comparison with a superlattice in the presence of a constant (dc)
and high-frequency (ac) electric fields. The electric current density
expression is derived using the semiclassical Boltzmann transport equation with
a constant relaxation time with the electric field applied along the nanotube
axis. Our analysis on the current density versus electric field characteristics
demonstrates negative differential conductivity at high frequency as well as
photon assisted peaks. The characteristic peaks are about an order of magnitude
styronger in the carbon nanotubes compared to superlattice. These strong
phenomena in carbon nanotubes can be used to obtain domainless amplification of
terahertz radiation in carbon nanotubes at room temperature.
