An improved small signal QWITT diode model including quantum well carrier lifetime effects

The authors present a novel small-signal model for the QWITT (quantum-well injection transit time) diode, which combines a recently proposed QWD (quantum-well diode) equivalent circuit with the distributed impedance model for the drift region. Both the QWD model and the QWITT model consider the effect of carrier delays in the quasi-bound state and drift region. To test QWD and QWITT models, the authors grew three different 5.1-nm-AlGaAs/5.1-nm-GaAs/5.1-nm-AlGaAs double-barrier structures by molecular beam epitaxy with different anode drift layer lengths. They obtained experimental impedance parameters for the fabricated diodes using an HP 8510B Automated Network Analyzer with cascade probes and fit the QWD and QWITT equivalent circuits to the data using analytical and numerical techniques. It is shown that QWDs and QWITTs are essentially the same device and may be modeled using the QWD or QWITT equivalent circuit with equal accuracy. The QWITT model is found to be preferable to the QWD model as a design tool because the drift region is treated separately