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This paper reviews recent advances in the research and development of graphene-based plasmonic metamaterials for terahertz (THz) laser transistors. The authors’ theoretical discovery on THz laser transistors in 2007 was realized as a distributed-feedback dual-gate graphene-channel field-effect transistor (DFB-DG-GFET) in 2018, demonstrating ∼0.1 µW single-mode emission at 5.2 THz and ∼80 µW amplified spontaneous 1–7.6 THz emission at 100 K. To realize room-temperature, dry-cell-battery operating intense THz lasing with fast direct modulation, various approaches based on graphene plasmonic metamaterials are investigated and introduced as real device implementations, including (i) replacement of the laser photonic cavity with plasmonic cavity enormously improving the THz photon field confinement with larger gain overlapping, (ii) introduction of THz amplification of stimulated emission via current-driven graphene Dirac plasmons (GDPs), and (iii) controlling the parity and time-reversal symmetry of GDPs enabling ultrafast direct gain-switch modulation. Possible real device structures and design constraints are discussed and addressed toward coherent light sources applicable to future 6G- and 7G-class THz wireless communication systems.

Due to their high optical phonon energies GaInP/AlGaInP heterostructures are a promising active medium to solve the problem of creating compact semiconductor sources with an operating frequency range of 5.5–7 THz. In this work, the temperature dependences of gain and absorption at 6.4–6.9 THz have been calculated for a GaInP/AlGaInP‐based quantum‐cascade laser (QCL) with two quantum wells in the cascade and a metal–metal waveguide. The dielectric function and mode losses for a 10 μm thick Au–Au waveguide, based on ternary InGaP and quaternary AlGaInP semiconductors, have been investigated in details. A laser structure that provides a mode gain of over 100 cm−1 with a maximum operating temperature about 100 K is proposed. The results of this study open the way to the development of a QCL for operation in a significant part of the GaAs phonon absorption band region, which is inaccessible for existing QCLs. [ABSTRACT FROM AUTHOR]

A distributed feedback dual-gate graphene-channel field-effect transistor (DFB-DG-GFET) was fabricated as a current-injection terahertz (THz) light-emitting laser transistor. We observed a broadband emission in a 1–7.6-THz range with a maximum radiation power of ~10 μW as well as a single-mode emission at 5.2 THz with a radiation power of ~0.1 μW both at 100 K when the carrier injection stays between the lower cutoff and upper cutoff threshold levels. The device also exhibited peculiar nonlinear threshold-like behavior with respect to the current-injection level. The LED-like broadband emission is interpreted as an amplified spontaneous THz emission being transcended to a single-mode lasing. Design constraints on waveguide structures for better THz photon field confinement with higher gain overlapping as well as DFB cavity structures with higher Q factors are also addressed towards intense, single-mode continuous wave THz lasing at room temperature.

A gas discharge is simulated and numerically studied in the gaseous helium in the region of the squeezed state of a single tubular magnetized relativistic electron beam at its partial reflection from a magnetic mirror. The code based on the particle‐in‐cell/Monte Carlo method was used. The electron beam dynamics, time evolution of phase portraits of particles, physical parameters, and spatial–time characteristics of plasma were calculated. It is shown that dense plasma appears in the cavity under the action of an electron beam in the form of a thin‐walled long cylinder of a large length; its electron concentration can be several units of 1011 cm−3. At the same time, it turned out that plasma is considerably inhomogeneous in length; its more dense part corresponds to the part of the squeezed state of a beam. The time dependence of the charge compensation of electrons on the helium atom concentration in the chamber was calculated. The dependence turned out to be decreasing since the rate of discharge development is increasing with the growth of the helium pressure in the cavity. [ABSTRACT FROM AUTHOR]