High-frequency (f similar to 1 THz) studies of quantum-effect devices

We have performed experimental, theoretical and simulation studies on the response of several types of antenna-coupled quantum-effect devices to high-frequency (f similar to 1 THz) radiation. The radiation-induced current in quantum point contact (QPC) devices is mainly due to heating. 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 are dominated by heating. Our simulation study also shows that photon excitations can be more easily achieved in double- and multiple-barrier structures. The localized nature of the quasibound states in these structures provides the momentum spread that relaxes the selection rule. Our experimental investigation of a lateral dual-gate device has yielded radiation-induced currents with distinctively different features at different radiation frequencies. These frequency-dependent features are strong evidence that the observed radiation-induced current is due to a photonic effect that depends on the energy of individual photons.