Large-signal dynamics of resonant-tunneling diodes

A model for analyzing dynamic large-signal characteristics of double-barrier resonant-tunneling diodes (RTDs) is presented. The model is based on the analysis of dynamical trajectories in phase space, defined by the RTD bias and electron density in the RTD quantum well. We show that an accurate dynamic model can be reformulated in an approximate way, relying only on a directly measurable DC I-V curve and on few other RTD parameters, which could be easily estimated with simple DC calculations. We further demonstrate that a simple equivalent circuit, composed of a capacitor, inductor, and two resistors (RLRC), accurately describes the large-signal admittance of RTDs. The circuit elements can be described in terms of relaxation time, geometrical RTD capacitance, and low- and high-frequency resistors. The circuit has the very same structure as that previously derived for small-signal RTD admittance, although with deviating parameters, which are now dependent on the AC-signal amplitude. We show that the large-signal RTD relaxation time can be shorter and longer than the small-signal one. In the context of RTD oscillators, a shorter RTD relaxation time allows one to get higher output power at high frequencies. The availability of an accurate, general, but rather simple, physics-based model for analyzing large-signal RTD dynamics removes one of the major hindrances to the further development of sub-THz and THz RTD oscillators.