A Nonlinear Circuit Simulation of Switching Process in Resonant-Tunneling Diodes

A large-signal circuit model is used to compute the switching time for double-barrier resonant-tunneling diodes. The model consists of linear circuit elements plus a nonlinear I-V characteristic. The linear elements include a series resistor, a capacitor, and an inductor. The capacitance considers the charge accumulation, depletion in spacer layers, as well as charging-discharging of the quantum-well (QW) region. The inductance accounts for the delay of the current with respect to the voltage across the QW during the abrupt switching transition through the negative differential resistance region. A second-order Runge-Kutta method is used to solve for the switching transient, and then fit to experimental data for a high-quality InGaAs/AlAs resonant tunneling diode (RTD) using the QW inductance as a fitting parameter. Excellent agreement is found for the 10%-90% switching time with a calculated capacitance of 98 fF and a fitted inductance of 1300 pH. This large-signal inductance is approximately 7× greater than the small-signal inductance that has been successfully used to predict the fmax of RTDs such as the one tested here.