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 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.