Parametric resonance and RF-to-THz frequency conversion in semiconductor plasmonic crystals

We show that plasma excitations in nanoscale field-effect transistor structures with periodically alternating gated and ungated regions (plasmonic crystals) exhibit a band structure with finite curvature (effective mass), in contrast to the linear and square-root dispersions of gated and ungated plasmons. These modes can be excited by synchronous gate-voltage pumping, avoiding the spatial nonuniformities of current-driven excitation. When the modulation drives the gated regions across threshold, the system enters a strongly nonlinear regime in which periodic modulation of the channel capacitance provides a parametric drive described by a generalized Mathieu equation. Depending on damping, this leads to either damped response or parametric instability. The resulting nonlinear dynamics generates a broad harmonic spectrum, enabling RF-to-THz frequency upconversion. Estimated drive conditions are compatible with existing millimeter-wave sources, including Schottky-diode multiplier chains and Gunn-diode oscillators.