We have performed experimental, theoretical and simulation studies on
the response of several types of antenna-coupled quantum-effect device
s to high-frequency (f similar to 1 THz) radiation. The radiation-indu
ced current in quantum point contact (QPC) devices is mainly due to he
ating. Our simulation study indicates that the selection rule forbids
photon-excited transitions between two extended electronic states, as
in the case for QPCs, if the radiation field is not tightly confined.
This key understanding may explain why the observed signals in QPCs ar
e dominated by heating. Our simulation study also shows that photon ex
citations can be more easily achieved in double- and multiple-barrier
structures. The localized nature of the quasibound states in these str
uctures provides the momentum spread that relaxes the selection rule.
Our experimental investigation of a lateral dual-gate device has yield
ed radiation-induced currents with distinctively different features at
different radiation frequencies. These frequency-dependent features a
re strong evidence that the observed radiation-induced current is due
to a photonic effect that depends on the energy of individual photons.