We have shown, firstly, that there response time (#tau#(resp)) of the double-barrier resonant-tunnelling diode (RTD) can be much smaller as well as much larger than the quasibound-state lifetime in the quantum well (#tau#(dwell)). Secondly, the real part of the RTD conductance can be negative and large at the frequencies higher than the reciprocal (#tau#(dwell)) in the RTDs with a heavily doped collector without spacer layers. The Coulomb interaction of the electrons in the quantum well with emitter and collector is responsible for the effects. A simple analytical expression for the impedance of the RTD has been derived and an equivalent circuit has been proposed.
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