Plasmonic Crystals with Tunable Band Gaps in the Grating Gate Transistor Structures

Abstract: We developed a hydrodynamic model of plasmonic crystals formed in the current-driven grating gate transistor structures. The model demonstrates that the quality factor of plasmonic resonances could be increased by using ungated regions with high electron densities connecting multiple plasmonic cavities. The analytical and numerical calculations of the EM radiation absorption by the band plasmons show that the drive current makes all plasma modes optically active by breaking the symmetry of the plasma oscillations. This effect results in splitting plasmon resonant absorption peaks revealing the gaps in the plasmonic band spectrum tunable by current. The analyzed design could achieve resonant behavior at room temperature for plasmonic crystals implemented in various material systems, including graphene, III-V, III-N materials, and p-diamond. We argue that the resulting double-peak spectrum line in the terahertz range also facilitates the absorption at the gap frequency, typically in microwave range. Power pumping at the gap frequency enables excitation of the gap plasmons, promoting frequency conversion from microwave to THz ranges. The flexibility in the length of the ungated region for the investigated structures allows for an effective coupling with THz radiation, with the metal grating acting as a distributive resonant antenna. The applications of the presented results extend to THz communication systems, THz sensing and imaging, frequency conversion systems, and other advanced THz plasmonic devices.