  This is a brief overview of the main physical ideas for application of field
effect transistors for generation and detection of TeraHertz radiation.
Resonant frequencies of the two-dimensional plasma oscillations in FETs
increase with the reduction of the channel dimensions and reach the THz range
for sub-micron gate lengths. When the mobility is high enough, the dynamics of
a short channel FET at THz frequencies is dominated by plasma waves. This may
result, on the one hand, in a spontaneous generation of plasma waves by a dc
current and on the other hand, in a resonant response to the incoming
radiation. In the opposite case, when plasma oscillations are overdamped, the
FET can operate as an efficient broadband THz detector.
