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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.

We propose the far-infrared and terahertz emitting diodes (FIR-EDs and THz-EDs) based on the graphene-layer/black phosphorus (GL/b-P) and graphene-layer/MoS2 (GL/MoS2) heterostructures with the lateral hole and vertical electron injection and develop their device models. In these EDs, the GL serves as an active region emitting the FIR and THz photons. Depending on the material of the electron injector, the carriers in the GL can be either cooled or heated dictated by the interplay of the vertical electron injection and optical phonon recombination. The proposed EDs based on GL/b-P heterostructures can be efficient sources of the FIP and THz radiation operating at room temperature.

We introduce a new scheme of actively controlling the P T symmetry of the graphene Dirac plasmon metasurface in a graphene-channel laser transistor structure. Numerical simulation demonstrates the capability of 100-Gbit/s-class ultrafast gain-switching in its plasmonic THz laser operation by electrically modulating the P T symmetry by the applied bias voltages.

We demonstrate that the injection of the ballistic electrons into the two-dimensional electron plasma in lateral ${n}^{+}$-$i$-$n$-${n}^{+}$ graphene field-effect transistors (GFETs) might lead to a substantial Coulomb drag of the quasiequilibrium electrons due the violation of the Galilean and Lorentz invariance in the systems with a linear electron dispersion. This effect can result in S-shaped current-voltage ($I$-$V$) characteristics. The resulting negative differential conductivity enables the hysteresis effects and current filamentation that can be used for the implementation of voltage-switching devices. Due to a strong nonlinearity of the $I$-$V$ characteristics, the GFETs can be used for an effective frequency multiplication and detection of terahertz radiation.

In this work we propose and analyze the possibility of creating terahertz plasmon-emitting graphene-channel transistor. It is shown that at electric pumping the damping of the terahertz plasmons can give way to their amplification, when the real part of the dynamic conductivity of graphene becomes negative in the terahertz range of frequencies due to the interband population inversion.

We review recently proposed concepts of infrared and terahertz photodetectors based on graphene van der Waals heterostructures and HgTe-CdHgTe quantum well heterostructures and demonstrate their potential.

We evaluate the characteristics of the vertically stacked graphene-layer infrared photodetector (VS-GLIP). Each period of the stack (which constitutes the GLIP) consists of a GL (serving as a photosensitive element with a floating potential) sandwiched between barrier layers made of the van der Waals materials, and highly conducting emitter and collector contact n-GLs. The operation of VS-GLIPs is associated with the interband photoexcitation of electrons from the GLs (direct or followed by the tunneling), injection of the electrons from the emitter layer and the collection of both the photoexcited and injected electrons by the collector layer. At a small probability of the electron capture into the floating GLs, each GLIP section exhibits an elevated photoconductive gain. Due to the vertical multi-GLIP structure the absorption efficiency can be close to unity. Due to this and because the photocurrents produced by each GLIP in the stack are summarized, the VS-GLIP can exhibit elevated detector responsivity and detectivity, in particular, exceeding those of the GLIPs.

Electrons and holes in graphene behave as relativistic charged massless Dirac fermions due to the graphene unique gapless electronic band structure with a linear dispersion law. Dirac plasmons - the quanta of the plasma oscillation of the Dirac electrons - can dramatically enhance the interaction of terahertz (THz) photons with graphene. We have proposed an original current-injection graphene THz laser transistor, demonstrated single-mode THz laser oscillation at low temperatures [1-3], and discovered and demonstrated the THz giant gain enhancement effect by the graphene Dirac plasmons [4-8]. However, further breakthroughs are needed to realize room-temperature high-intensity THz lasing and ultrafast modulation operation for the next generation wireless 6G and 7G communications. In this paper, we will present new ideas on the operating principle and device structures of the THz graphene plasmonic laser transistors with a high radiation intensity and ultrafast modulation capability operating at room temperature. To dramatically improve the quantum efficiency and gain, we utilize the Coulomb drag effect in lateral n+ - i – n - n+ graphene diode/transistor structures with the ballistic injection of the graphene Dirac fermions [9-11]. Such injection strongly modifies the current-voltage characteristics producing “plasmonic gain” in the THz frequency range applicable for THz oscillations and amplifications. This phenomenon is associated with the specifics of the ballistic electron scattering on quasi-equilibrium electrons in graphene. Depending on the device structural parameters (in particular, the gated region length and its electron Fermi energy), the graphene diode/transistor structures can exhibit either S-shaped or monotonic current-voltage characteristics [9]. In the former case, the resulting hysteresis and current filamentation effects can be used for the implementation of the voltage-switching devices. The feedback between the amplified dragged electrons current and the injected ballistic electrons current can lead to the negative THz dynamic conductivity. The self-excitation of the THz plasma oscillations in the gated region enables the realization of the graphene transistor-based sources of THz radiation [11]. To realize ultrafast modulation of lasing intensity/phase, we introduce actively controlling the parity and time-reversal (PT) symmetry [12] of the graphene Dirac plasmons (GDPs) in the dual-grating-gate graphene-channel field effect transistor (DGG-GFET) nanostructures for the ultrafast modulation of the lasing intensity and phase. [13]. The PT symmetry is expressed by a pair of complementary gain and loss elements. This gain–loss balance leads to the exceptional points at the real frequency axis in the exact PT-phase resulting in the extraordinary frequency response of “unidirectionality” [14]. The DGG-GDP metasurface, which consists of a unit cell comprising a pair of gain and loss regions and its periodical arrangement, promotes the GDP instability. The PT symmetry can be controlled (to be held or broken) by altering the gate or drain bias voltages. Our numerical simulations showed that the laser cavity Q values can be dynamically controllable in a DGG-GDP transistor structure [6] demonstrating 100-Gbit/s-class ultrafast modulation capabilities [13]. The authors thank A.A. Dubinov, D. Yadav, T. Watanabe, T. Suemitsu, W. Knap, V. Kachorovskii, and V.V. Popov for their contributions. This work was supported by JSPS-KAKENHI No. 21H04546, and No. 20K20349, Japan. V. Ryzhii, M. Ryzhii, and T. Otsuji, J. Appl. Phys. 101, 083114 (2007). T. Otsuji et al., IEEE J. Sel. Top. Quantum Electron. 19, 8400209 (2013). D. Yadav et al., Nanophoton. 7, 741-752 (2018). A.A. Duvinov el al., J. Phys.: Cond. Matters 23, 145302 (2011). T. Watanabe et al., New J. Phys. 15, 075003 (2013). Y. Koseki et al., Phys. Rev. B 93, 245408 (2016). S. Boubanga-Tombet et al., Phys. Rev. X 10, 031004 (2020). S. Boubanga-Tombet et al., Front. Phys. 9, 726806 (2021). V. Ryzhii et al., Phys. Rev. Appl. 16, 014001 (2021). V. Ryzhii et al., Appl. Phys. Lett. 119, 093501 (2021). V. Ryzhii et al., Physica Status Solidi A 218, 2100535 (2021). M.-A. Miri and A. Alu, Science 363, eaar7709 (2019). T. Otsuji et al., Nanophoton. under review. H. Ramezani and T. Kottos, Phys. Rev. A 82, 04383 (2010). Figure 1

We propose far-infrared photodetectors with the graphene nanoribbon (GNR) array as the photosensitive element and the black phosphorus (bP) base layer (BL). The operation of these GNR infrared photodetectors (GNR-IPs) is associated with the interband photogeneration of the electron–hole pairs in the GNR array followed by the tunneling injection of either electrons or holes into a wide gap bP BL. The GNR-IP operating principle is akin to that of the unitraveling-carrier photodiodes based on the standard semiconductors. Due to a narrow energy gap in the GNRs, the proposed GNR-IPs can operate in the far-, mid-, and near-infrared spectral ranges. The cut-off photon energy, which is specified by the GNR energy gap (i.e., is dictated by the GNR width), can be in the far-infrared range, being smaller that the energy gap of the bP BL of ΔG ≃ 300 meV. Using the developed device models of the GNR-IPs and the GNR-IP terahertz photomixers, we evaluate their characteristics and predict their potential performance. The speed of the GNR-IP response is determined by rather short times: the photocarrier try-to-escape time and the photocarrier transit time across the BL. Therefore, the GNR-IPs could operate as terahertz photomixers. The excitation of the plasma oscillations in the GNR array might result in a strong resonant photomixing.

We develop the device model for the proposed injection (electrically) driven thermal light emitters (IDLEs) based on the vertical Hexagonal Boron Nitride Layer/Graphene Layer/ Hexagonal Boron Nitride Layer (hBNL/GL/hBNL) heterostructures and analyze their dynamic response. The operation of the IDLEs is associated with the light emission of the hot two-dimensional electron-hole plasma (2DEHP) generated in the GL by both the lateral injection from the side contacts and the vertical injection through the hBNL (combined injection) heating the 2DEHP. The temporal variation of the injection current results in the variation of the carrier effective temperature and their density in the GL leading to the modulation of the output light. We determine the mechanisms limiting the IDLE efficiency and the maximum light modulation frequency. A large difference between the carrier and lattice temperatures the IDLEs with an effective heat removal enables a fairly large modulation depth at the modulation frequencies about dozen of GHz in contrast to the standard incandescent lamps. We compare the IDLEs with the combined injection under consideration and IDLEs using the carrier Joule heating by lateral current. The obtained results can be used for the IDLE optimization., 19 pages, 6 figures

We propose the far-infrared and terahertz emitting diodes (FIR-EDs and THz-EDs) based on the graphene-layer/black phosphorus (GL/b-P) and graphene-layer/MoS

We develop the device models for the far-infrared interband photodetectors (IPs) with the graphene-layer (GL) sensitive elements and the black Phosphorus (b-P) or black-Arsenic (b-As) barrier layers (BLs). These far-infrared GL/BL-based IPs (GBIPs) can operate at the photon energies ℏ Ω smaller than the energy gap, Δ G , of the b-P or b-As or their compounds, namely, at ℏ Ω ≲ 2 Δ G / 3 corresponding to the wavelength range λ ≳ ( 6 − 12 ) μ m. The GBIP operation spectrum can be shifted to the terahertz range by increasing the bias voltage. The BLs made of the compounds b-As x B1−x with different x, enable the GBIPs with desirable spectral characteristics. The GL doping level substantially affects the GBIP characteristics and is important for their optimization. A remarkable feature of the GBIPs under consideration is a substantial (over an order of magnitude) lowering of the dark current due to a partial suppression of the dark-current gain accompanied by a fairly high photoconductive gain. Due to a large absorption coefficient and photoconductive gain, the GBIPs can exhibit large values of the internal responsivity and dark-current-limited detectivity exceeding those of the quantum-well and quantum-dot IPs using the intersubband transitions. The GBIPs with the b-P and b-As BLs can operate at longer radiation wavelengths than the infrared GL-based IPs comprising the BLs made of other van der Waals materials and can also compete with all kinds of the far-infrared photodetectors.

We analyze the statistical characteristics of the quasi-nonequilibrium two-dimensional electron-hole plasma in graphene layers (GLs) and graphene bilayers (GBLs) and evaluate their heat capacity.The GL heat capacity of the weakly pumped intrinsic or weakly doped GLs normalized by the Boltzmann constant is equal to $c_{GL} \simeq 6.58$. With varying carrier temperature the intrinsic GBL carrier heat capacity $c_{GBL}$ changes from $c_{GBL} \simeq 2.37$ at $T \lesssim 300$~K to $c_{GBL} \simeq 6.58$ at elevated temperatures. These values are markedly differentfrom the heat capacity of classical two-dimensional carriers with $c = 1$. The obtained results can be useful for the optimization of different GL- and GBL-based high-speed devices., Comment: 6 pages, one figure

We analyze the operation of the graphene n+-i-n-n+ field-effect transistors (GFETs) and lateral diodes (GLDs) with the injection of ballistic electrons into the n-region. The momentum transfer of the injected ballistic electrons could lead to an effective Coulomb drag of the quasi-equilibrium electrons in the n-region and the plasma instability in the GFETs and GLDs. The instability enables the generation of terahertz radiation. The obtained results can be used for the optimization of the structures under consideration for different devices, in particular, terahertz emitters., Comment: 8 pages, 4 figures

We compare the characteristics of the intersubband quantum-well infrared photodetectors (QWIPs) based on the traditional semiconductor materials and the interband graphene-layer infrared photodetectors (GLIPs) based on van der Waals heterostructures. We show that the responsivity and dark-current-limited detectivity of GLIPs exceed those of QWIPs. This is because of a stronger radiation interband absorption in the GLs, a smaller capture probability of electrons into the GLs, and a higher activation energy of the electron thermionic and tunneling escape from the GLs in comparison with those in the QWs.

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.

We report on the detection of sub-terahertz radiation using single layer graphene and graphene-nanoribbon FETs with asymmetric contacts (one is the Schottky contact and one – the Ohmic contact). We found that cutting graphene into ribbons a hundred nanometers wide leads to a decrease of the response to sub-THz radiation. We show that suppression of the response in the graphene nanoribbons devices can be explained by unusual properties of the Schottky barrier on graphene-vanadium interface.

We predict the self-excitation of terahertz (THz) oscillations due to the plasma instability in the lateral n+-i-n-n+$ graphene field-effect transistors (G-FET). The instability is associated with the Coulomb drag of the quasi-equilibrium electrons in the gated channel by the injected ballistic electrons resulting in a positive feedback between the amplified dragged electrons current and the injected current. The plasma excitations arise when the drag effect is sufficiently strong. The drag efficiency and the plasma frequency are determined by the quasi-equilibrium electrons Fermi energy (i.e., by their density). The conditions of the terahertz plasma oscillation self-excitation can be realized in the G-FETs with realistic structural parameters at room temperature enabling the potential G-FET-based radiation sources for the THz applications., 5 pages, 3 figures

We analyze the modulation characteristics of the uncooled terahertz (THz) and infrared (IR) detectors using the variation of the density and effective temperature of the two-dimensional electron-hole plasma in uniform graphene layers (GLs) and perforated graphene layers (PGLs) due to the absorption of THz and IR radiation. The performance of the photodetectors (both the GL-photoresistor and the PGL-based barrier photodiodes) are compared. Their characteristics are also compared with the GL reverse-biased photodiodes. The obtained results allow to evaluate the ultimate modulation frequencies of these photodetectors and can be used for their optimization., 10 pages, 3 figures

We propose the concept of the infrared detection and photon energy up-conversion in the devices using the integration of the graphene layer infrared detectors (GLIPs) and the light emitting diodes (LEDs) based on van der Waals (vdW) heterostructures. Using the developed device model of the GLIP-LEDs, we calculate their characteristics. The GLIP-LED devices can operate as the detectors of far- and mid infrared radiation (FIR and MIR) with an electrical output or with near-infrared radiation (NIR) or visible radiation (VIR) output. In the latter case, GLIP-LED devices function as the photon energy up-converters of FIR and MIR to NIR or VIR. The operation of GLIP-LED devices is associated with the injection of the electron photocurrent produced due to the interband absorption of the FIR/MIR photons in the GLIP part into the LED emitting NIR/VIR photons. We calculate the GLIP-LED responsivity and up-conversion efficiency as functions the structure parameters and the energies of the incident FIR/MIR photons and the output NIR/VIR photons. The advantages of the GLs in the vdW heterostructures (relatively high photoexcitation rate from and low capture efficiency into GLs) combined with the reabsorption of a fraction of the NIR/FIR photon flux in the GLIP (which can enable an effective photonic feedback) result in the elevated GLIP-LED device responsivity and up-conversion efficiency. The positive optical feedback from the LED section of the device lead to increasing current injection enabling the appearance of the S-type current-voltage characteristic with a greatly enhanced responsivity near the switching point and current filamentation.

In [Phys. Rev. Lett. vol. 119, p. 133901 (2017)] it was argued that two parallel graphene layers in the presence of electron drift support unstable plasmon modes. Here we show that the predicted plasmon instability is an artifact of errors upon evaluation of graphene polarizability in the presence if electron drift. Crucial role of broken Galilean invariance and spatial dispersion of conductivity for suppression of plasmon instabilities is highlighted., Comment: 2 pages, 1 figure

We evaluate the optical pumping efficiency of the graphene-layer (GL) heterostructures intended for the terahertz (THz) lasing using the interband transitions in the GL. The pumping of such by near- or mid-infrared (NIR or MIR) radiation leads to the creation of a substantially hot two-dimensional electron-hole plasma (2D-EHP) in the GL. This hampers the interband population inversion in the 2D-EHP and can suppress the THz lasing. To prevent the 2D-EHP overheating, we propose to use the NIR/MIR radiation pumping of the GL through a sufficiently thick layer absorbing this radiation. This layer with sufficiently small energy gap enables an increase in the quantum efficiency of the pumping accompanied by strong cooling of the electron-hole pairs injected into the GL. As shown, the absorbing-cooling layers made of black-arsenic-phosphorus can be fairly efficient if their energy gap is smaller than the optical phonon energy in the GL.

We propose and evaluate the heterostructure based on the graphene layer (GL) with the lateral electron injection from the side contacts and the hole vertical injection via the black phosphorus layer (BL) $({\mathrm{P}}^{+}\text{\ensuremath{-}}\mathrm{PL}$-PL-GL heterostructure). Due to a relatively small energy of the holes injected from the PL into the GL (about 100 meV, smaller than the energy of optical phonons in the GL which is about 200 meV), the hole injection can effectively cool down the two-dimensional electron-hole plasma in the GL. This simplifies the realization of the interband population inversion and the achievement of the negative dynamic conductivity in the terahertz (THz) frequency range enabling the amplification of the surface plasmon modes. The latter can lead to the plasmon lasing. The conversion of the plasmons into the output radiation can be used for new types of the THz sources.

Current-injection pumping in graphene makes carrier population inversion enabling lasing and/or amplification of terahertz (THz) radiation. We have recently demonstrated single-mode THz lasing at 100K in graphene-channel transistor laser structures. Introduction of a gated double-graphene-layered (G-DGL) van der Waals heterostructure is a promising route to further increase the operation temperature and radiation intensity via plasmon- and/or photon-assisted quantummechanical tunneling. We have proposed a cascading of the G-DGL unit element working as a new type of THz quantumcascade lasers. Numerical analyses demonstrate further increase of the quantum efficiency of THz lasing by orders of magnitude compared to a transistor or single G-DGL structure.

Linear and gapless energy spectrum of graphene carriers enables population inversion under optical and electrical pumping. We first theoretically discovered this phenomenon and demonstrated experimental observation of single-mode THz lasing with rather weak intensity at 100K in current-injection pumped graphene-channel field-effect transistors (GFETs). We introduce graphene surface plasmon polariton (SPP) instability to substantially boost the THz gain. We demonstrate our experimental observation of giant amplification of THz radiation at 300K stimulated by graphene plasmon instabilities in asymmetric dual-grating gate (ADGG) GFETs. Integrating the graphene SPP amplifier into a GFET laser will be a promising solution towards room-temperature intense THz lasing.

This paper reviews recent advances in the terahertz (THz) graphene-based 2D-heterostructure lasers and amplifiers. The linear gapless graphene energy spectrum enables population inversion under optical and electrical pumping giving rise to the negative dynamic conductivity in a wide THz frequency range. We first theoretically discovered these phenomena and recently reported on the experimental observation of the amplified spontaneous THz emission and single-mode THz lasing at 100K in the current-injection pumped graphene-channel field-effect transistors (GFETs) with a distributedfeedback dual-gate structure. We also observed the light amplification of stimulated emission of THz radiation driven by graphene-plasmon instability in the asymmetric dual-grating gate (ADGG) GFETs by using a THz time-domain spectroscopy technique. Integrating the graphene surface plasmon polariton (SPP) oscillator into a current-injection graphene THz laser transistor is the most promising approach towards room-temperature intense THz lasing.

We propose and analyze the heterostructure comprising a black-arsenic-phosphorus layer (b-As$_{1-x}$P$_x$L) and a graphene layer (GL) integrated with a light-emitting diode (LED). The integrated b-As$_{1-x}$P$_x$L-GL-LED heterostructure can serve as an active part of the terahertz (THz) laser using the interband radiative transitions in the GL. The feasibility of the proposed concept is enabled by the combination of relatively narrow energy gap in the b-As$_{1-x}$P$_x$L and the proper band alignment with the GL. The operation of the device in question is associated with the generation of the electron-hole pairs by the LED emitted near-infrared radiation in the b-As$_{1-x}$P$_x$L, cooling of the photogenerated electrons and holes in this layer, and their injection into the GL. Since the minimum b-As$_{1-x}$PL energy gap is smaller than the energy of optical phonons in the GL, , the injection into the GL can lead to a relatively weak heating of the two-dimensional electron-hole plasma (2D-EHP) in the GL. At the temperatures somewhat lower than the room temperature, the injection can cool the 2D-EHP. This is beneficial for the interband population inversion in the GL, reinforcement of its negative dynamic conductivity, %in the THz range and the realization of the optical and plasmonic modes lasing supporting the new types of the THz radiation sources., Comment: 10 pages, 4 figures

A fitting model is developed for accounting the asymmetric ambipolarities in the $I$ – $V$ characteristics of graphene FETs (G-FETs) with doped channels, originating from the thermionic emission and interband tunneling at the junctions between the gated and access regions. Using the model, the gate-voltage-dependent intrinsic mobility as well as other intrinsic and extrinsic device parameters can be extracted. We apply it to a top-gated G-FET with a graphene channel grown on a SiC substrate and with SiN gate dielectric that we reported previously, and we demonstrate that it can excellently fit its asymmetric $I$ – $V$ characteristic.

InP-based high electron mobility transistors (InP-HEMTs) and graphene-channel FETs (G-FETs) are experimentally examined as photonic frequency converters for future broadband optical and wireless communication systems. Optoelectronic properties and three-terminal functionalities of the InP-HEMTs and G-FETs are exploited to perform single-chip photonic double-mixing operation over the 120 GHz wireless communication band. A 10 Gbit/s-class data signal on a 112.5 GHz carrier is mixed down to a 25 GHz IF band with an 87.5 GHz LO signal that is simultaneously self-generated from an optically injected photomixed beat note. The results suggest that the intrinsic channel of the G-FET can achieve a speed performance that is superior to that of an InP-HEMT having an equivalent device feature size. The reduction of the extrinsic parasitic resistances and the implementation of an efficient photo-absorption structure in the G-FET may allow a millimeter-wave and sub-THz photonic frequency conversion with a sufficiently high conversion gain for practical purposes.

The development of compact, low-cost sources and detectors operating at room temperature is needed to fully use terahertz (THz) electromagnetic waves in a variety of applications. Photo-excited graphene is expected to exhibit population inversion and enable the fabrication of a novel THz laser. We previously proposed a THz amplifier as a basic element in a THz laser by combining the population inversion in photo-excited graphene with the electric field enhancement due to the spoof surface plasmon polaritons induced on the surface of a metal mesh structure. For this work, we fabricated prototype THz amplifiers composed of chemical-vapor-deposition-grown graphene and a metal mesh structure and observed extremely amplified THz emission by using an electro-optic sampling method.

We analyze terahertz superluminescent and laser diodes using the injection pumping in the multiple graphene-layer (GL)/van der Waals barrier layers (BLs) heterostructures. The operation of such terahertz radiation sources is associated with the interband transitions in the gapless GLs under the population inversion leading to the GL negative dynamic conductivity. These devices use the lateral injection of holes and vertical injection of electrons. Such an injection might have advantages over the lateral injection of the bipolar carriers. Due to relatively large conduction band offsets at the GL-BL interface, the population inversion at the vertical injection can be markedly hampered by the injection current heating of the two-dimensional electron-hole plasma (2DEHP) in the GLs. We show that doping GLs and/or BLs can substantially diminish the carrier heating promoting the interband population. Numerical analysis assumed the BL material parameters of MoS2 and WSe2 and showed the feasibility of such terahertz radiation sources.

Unique properties of graphene are combined to enable graphene plasmonic devices that could revolutionize the terahertz (THz) electronic technology. A high value of the carrier mobility allows us to excite resonant plasma waves. The graphene bipolar nature allows for different mechanisms of plasma wave excitation. Graphene bilayer and multilayer structures make possible improved THz device configurations. The ability of graphene to form a high quality heterostructure with h-BN, black phosphorus, and other materials systems supports advanced heterostructure devices comprised of the best properties of graphene and other emerging materials. In particular, using black phosphorus compounds for cooling electron–hole plasma in graphene could dramatically improve the conditions for THz lasing. High optical phonon energy allows for reaching higher plasma frequencies that are supported by high sheet carrier densities in graphene. Recent improvements in graphene technology combined with a better understanding of the device physics of graphene THz plasmonics and graphene plasmonic device designs hold promise to make graphene THz plasmonic technology one of the key graphene applications. Commercialization of plasmonic graphene technology is facing the same challenges as other graphene applications, which have difficulties in producing uniform large graphene layers, bilayers, and heterostructures of high quality and making good low resistance stable Ohmic contacts. The time projection for large scale graphene electronic device applications now extends into the 2030s. However, emerging graphene mass production technologies might bring commercial applications of the graphene plasmonic terahertz technology closer.

We analyze the pumping of the graphene-based laser heterostructures by infrared radiation using the numerical model. To enable the injection of sufficiently cooled carriers into the graphene layer (GL) leading to the interband population inversion, we propose to use the graded-gap black-PxAs1 − x absorption-cooling layers. Our calculations are based on the thermodiffusion-drift carrier transport model. We demonstrate that the proposed optical pumping method can provide an efficient injection of the cool electron–hole plasma into the GL and the interband population inversion in the GL. Since the energy gap in b-As layer can be smaller than the energy of optical phonons in the GL, the injected electron–hole plasma can be additionally cooled down to the temperatures lower than the lattice temperature. This promotes a stronger population inversion that is beneficial for realization of the GL-based optically pumped terahertz and far-infrared laser, plasmon emitters, and the superluminescent downconverters. We also compare the efficiency of optical pumping through the graded-gap and uniform absorbing-cooling layers.

We report on the design, evaluation and fabrication of the sub-terahertz (sub-THz) detector using a GaAs gated field-effect transistor with a buried quasi-two-dimensional electron gas created by the self-assembled Sn-nanothreads (Sn-NTs) embedded into the GaAs channel. This GaAs-Sn-NTs detector efficiently detects a sub- THz radiation at cryogenic and room temperatures (CT and RT respectively). Two possible detection mechanisms are the bolometric mechanism due to electron heating by the sub-THz radiation and the mechanism related to the rectification of the decayed plasmonic oscillations. We developed a classical self-consistent device model of the bolometric detection involving the Poisson equation and the electron density of states and estimated responsivity and noise-equivalent power of the detector. The measured I-V characteristics and the photoresponse to the incident sub-THz radiation at CT and RT are in reasonable agreement with our model. The detector demonstrates a better performance than semiconductor-based hot-electron bolometers and quantum-well/dot IR and THz photodetectors.

We consider the effect of terahertz (THz) radiation on the conductivity of the ungated and gated graphene (G)-phosphorene (P) hybrid structures and propose and evaluated the hot-carrier uncooled bolometric photodetectors based on the GP-lateral diodes (GP-LDs) and GP-field-effect transistors (GP-FETs) with the GP channel. The operation of the GP-LDs and GP-FET photodetectors is associated with the carrier heating by the incident radiation absorbed in the G-layer due to the intraband transitions. The carrier heating leads to the relocation of a significant fraction of the carriers into the P-layer. Due to a relatively low mobility of the carriers in the P-layer, their main role is associated with a substantial reinforcement of the scattering of the carriers. The GP-FET bolometric photodetector characteristics are effectively controlled by the gate voltage. A strong negative conductivity of the GP-channel can provide much higher responsivity of the THz hot-carriers GP-LD and GP-FET bolometric photodetectors in comparison with the bolometers with solely the G-channels., Comment: 12 pages, 5 figures

We report on photonic frequency double-mixing conversion utilizing a graphene-channel FET (G-FET). Optoelectronic properties of graphene are exploited to perform single-chip photonic double-mixing functionality, which is greatly advantageous in future broadband technological conversion between optical fiber and sub-terahertz wireless communications. A 1 GHz modulation signal on a 125 GHz carrier is electrically input to the gate, whereas a 1.58 μm dual wavelength CW laser beam having a frequency difference of 112.5 GHz impinges on the G-FET. The G-FET works as a photomixer generating a 112.5 GHz local signal which is then electrically mixed to the 1 GHz modulated 125 GHz carrier signal, resulting in the down-conversion of the 1 GHz signal to a 12.5 GHz intermediate frequency (IF) signal.

We review the performance of terahertz and infrared graphene photodetectors using heterostructures enabled by van der Waals bonding and the application of these devices for up-conversion to visible or UV range.

We report on amplified spontaneous broadband terahertz emission in 1–7.6 THz range at 100 K via current injection in a distributed-feedback dual-gate graphene-channel field effect transistor (DFB-DG GFET). The device exhibited a nonlinear threshold-like behavior with respect to the current-injection level. A precise DFB cavity design is expected to transcend the observed spontaneous broadband emission to single-mode THz lasing.