Terahertz plasmonic sources

Abstract

Oscillations of the electron density (plasma waves) in the channels of field effect transistors (FETs) propagate with velocities much larger than typical electron drift velocities. FETs operating in the plasmonic regime (TeraFETs) could detect and emit terahertz (THz) and sub-THz radiation. The TeraFET plasmonic detectors have demonstrated excellent performance and are now being commercialized and used as pixels of THz cameras. New ideas of TeraFET THz detection breaking symmetry by phase enable TeraFET THz spectrometers and THz line-of-sight detectors. Heterodyne modes of operation and operation under bias increase the TeraFET sensitivity by orders of magnitude. The challenge now is to develop compatible TeraFET plasmonic sources, which, in combination with TeraFET plasmonic detectors, will support THz and sub-THz communications, including beyond 5G – 6G WiFi in the 240 GHz to 320 GHz range. Many other applications of such sources range from radio astronomy to industrial controls, security, biomedical, pharmaceutical, compact radar, drone, VLSI testing, and IoT applications. Silicon ultra-short channel MOS, AlGaN/GaN and AlGaAs/InGaAs HEMTs, p-diamond and graphene transistors are all candidates for the TeraFET plasmonic sources. Such sources are driven by a ballistic or quasi-ballistic current leading to a plasma wave instability. The instability mechanisms range from the Dyakonov-Shur instability involving the reflection of the plasma waves carried by drift, the instability using the transit time delays, and the “plasmonic boom” instability arising when the electron drift velocity crosses the plasma velocity. Even though the instability increments are reduced by the electron (or hole) scattering and by the electron viscosity the analysis of the TeraFET performance for different materials systems show that the room temperature operation is possible. The grating gate structures should allow to obtain sufficient powers and efficiencies. Our estimates show that it is possible to achieve 100 mW power at 1 THz. I estimate that it would take from 3 to 5 years for the THz plasmonic sources to reach practical Technology Readiness Levels for commercial applications.