Graphene-Based Plasmonic Terahertz Laser Transistors

This chapter reviews recent advances in the research of graphene-based plasmonic terahertz laser transistors. Optically or electrically pumped graphene works as a gain medium in the terahertz frequency range. The author’s group theoretically discovered this fact and experimentally verified the single mode terahertz emission, as well as broadband terahertz amplified spontaneous emission from fabricated graphene-channel field-effect transistor (GFET) laser chips. However, its lasing threshold temperature was low (100 K) and emission intensity was weak. To drastically improve the laser performance, the introduction of graphene Dirac plasmons (GDPs) as the gain booster is promising. The author’s group found a novel way to promote the current-driven instability of the GDPs in an asymmetric dual-grating-gate GFET, demonstrating room-temperature amplification of stimulated emission of terahertz radiation with the maximal gain of 9% which is four times larger than the quantum-mechanical limit when terahertz photons directly interact with graphene electrons without excitation of the GDPs. The author also proposes the active controlling of the parity and time-reversal symmetries of the GDPs as a paradigm towards ultrafast direct gain switching in the GFET lasers. Future directions to unite the gain seed and amplifier sections in a single GFET structure will be addressed with several feasible scenarios.