Improved Small-Signal Analysis of the Quantum-Well Injection Transit Time Diode

Two improved methods are developed for calculating the small-signal impedance of the quantum-well injection transit time (QWITT) diode. The first extends the traditional analysis to include carrier velocity transient effects, producing an analytical expression from which optimum injection conductance and drift angle may be found. The second method includes the effects of both nonuniform carrier velocity and diffusion, casting the expression for impedance in terms of a double integration that is evaluated numerically. A lumped-element model is developed that closely duplicates the impedance found by the numerical method. A graphical means is provided that allows the generation of the lumped-element model from the dc negative resistance and knowledge of the diode structure. The more sophisticated models developed in this paper should be useful in device design, evaluation of mounting and packaging schemes, and for suppression of unwanted oscillations.