Does the quasibound-state lifetime restrict the high-frequency operation of resonant-tunnelling diodes?

We have shown, firstly, that the 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.