Optimization of the QWITT diode using equivalent circuit models

An investigation is conducted of an equivalent circuit and an equivalent circuit-distributed impedance model for the QWITT (quantum-well injection transit time) diode. Both models incorporate a negative inductor to model the finite lifetime of carriers in the quantum well. For the latter model, the cutoff frequency and the negative resistance can be optimized with respect to the drift region length, W. It is predicted and experimentally confirmed at low values of W that the cutoff frequency increases with W. The two models diverge as W increases and the drift angle is found to be a good predictor for this behavior.<>