Abstract-Terahertz plasmon amplification in a double-layer graphene structure with direct electric current in hydrodynamic regime

 

I. M. Moiseenko, V. V. Popov, D. V. Fateev, 

https://journals.aps.org/prb/accepted/3b074Of7Pa2Ea210634e99e143a55ddc10d0d1a0b

The possibility of excitation and amplification of terahertz plasmons in a structure containing a layer of graphene with charge carrier drift and a layer of graphene without carrier drift is theoretically investigated. The plasmon excitation in the graphene structure by an incident terahertz electromagnetic wave is calculated in the attenuated total reflection geometry. It is shown that, in graphene with charge carrier drift, it is possible to achieve negative values of the real part of graphene conductivity for the phase velocity of plasmons exceeding the charge carriers drift velocities, which indicates a non-Cherenkov amplification of terahertz plasmons in the double-layer graphene structure for practically achievable direct electric current values. Terahertz amplification originates due to the variation of the carrier mass density in graphene with terahertz electric field. In the case of weak deceleration of terahertz wave incident onto graphene structure, the value of the negative conductivity of graphene does not depend on the direction of the direct current in graphene (only the co-directional and counter-directional currents with respect to the direction of plasmon propagation are considered). This is due to the insignificant spatial dispersion of the hydrodynamic conductivity of graphene in the case of weak deceleration of terahertz waves. The results of this work can be used to create compact terahertz radiation amplifiers operating at room temperature. The investigations of plasmonic properties of graphene structures for amplification, generation, detection and modulation of terahertz (THz) radiation an actively exploring area of nanophotonics in recent years [1-10]. Graphene conductivity in THz frequency range can be described by using a hydrodynamic approach in the case when the frequency of acting electromagnetic field and the electron momentum relaxation rate in graphene is smaller than the frequency of carrier-carrier collisions [11, 12]. The hydrodynamic regime of graphene at THz frequencies is confirmed in experimental works, in which the current vortices in graphene are discovered [13, 14.]. In general, the carrier drift in graphene, the carrier pressure forces, as well as the influence of the Doppler effect in graphene leads to the spatial dispersion of the graphene hydrodynamic conductivity. The Doppler effect results in Cherenkov amplification, which is difficult to achieve in two-dimensional isotropic parabolic materials [15, 16]. The amplification of THz radiation in single-layer and double-layer graphene structures due to the radiative recombination of charge carriers and obtaining the negative dynamic conductivity of graphene by different methods of graphene pumping were investigated [17-19]. However, creating a long-lived inversion in graphene is a difficult task due to the strong non-radiative recombination of charge carriers in graphene [12, 20] and strong heating of the structures by high pumping power. The problem of graphene heating can be solved by using the diffusion pumping of graphene on a black-As substrate [21]. Experimental observation of optical (2.0–3.5 eV range) emission from graphene induced by an intense THz pulse is reported in [22]. An alternative mechanism of amplification of THz radiation in graphene is the Cherenkov plasmon instability, which can occur in graphene when a direct electric current is passed in the plane of graphene [23]. 

Abstract-Smaller antenna-gate gap for higher sensitivity of GaN/AlGaN HEMT terahertz detectors

Applied Physics Letters

Zhipeng Zhang, Xiang Li, Hua Qin, Jinfeng Zhang, Xinxing Li, Yang Shangguan, Lin Jin, Yunfei Sun, V. V. Popov,

(a) Schematic diagram of the GaN/AlGaN HEMT detector including the measurement circuit. (b) Zoom-in view of the central active region.

https://aip.scitation.org/doi/abs/10.1063/1.5142436

We report an attempt to improve the sensitivity of terahertz detection based on self-mixing in antenna-coupled field-effect transistors by enhancing the field-effect factor and the antenna factor with a reduced gate length and a reduced antenna-gate gap, respectively. An optical noise equivalent power (NEP) of 3.7 pW/Hz⎯⎯⎯⎯⎯√$3.7\hspace{0.17em}\text{pW}/\sqrt{\text{Hz}}$ at 0.65 THz was achieved in a GaN/AlGaN high-electron-mobility transistor (HEMT) with a gate length of 300 nm and an antenna-gate gap of 200 nm at room temperature. It was found that the antenna factor was inversely proportional to the antenna-gate gap, and the responses upon coherent/incoherent terahertz irradiation were well described by the self-mixing model. To fill the NEP gap of 0.1−1 pW/Hz⎯⎯⎯⎯⎯√$0.1-1\hspace{0.17em}\text{pW}/\sqrt{\text{Hz}}$ between room-temperature and cryogenic detectors by HEMT-based detectors at room temperature, impedance match needs to be carefully considered.

The authors acknowledge support from the National Natural Science Foundation of China (Nos. 61771466, 61775231, and 61975227), the Youth Innovation Promotion Association CAS (No. 2017372), the Six Talent Peaks Project of Jiangsu Province, China (XXRJ-079), and the Russian Foundation for Basic Research (No. 17-52-53063). The work in the Kotelnikov IRE RAS was carried out within the framework of the state task.

Abstract-Two-terminal terahertz detectors based on AlGaN/GaN high-electron-mobility transistors

Applied Physics Letters

Jiandong Sun, Zhipeng Zhang,  Xiang Li, Hua Qin, Yunfei Sun, Yong Cai, Guohao Yu, Zhili Zhang, Jinfeng Zhang, Yang Shangguan, Lin Jin, Xinxing Li, Baoshun Zhang,  V. V. Popov,

(a) A top view of the detector. (b) Central gate and fluorine ion implantation area of the detector. (c) A schematic cross section of the detector corresponding to the dotted red line in (b). (d) A color-scale 2D plot of the spatial distribution of the mixing factor from a FDTD simulation at 648 GHz.

https://aip.scitation.org/doi/abs/10.1063/1.5114682

We report an approach to make two-terminal antenna-coupled AlGaN/GaN high-electron-mobility-transistor self-mixing terahertz detectors. Fluorine ion implantation is used to increase the threshold voltage of the AlGaN/GaN two-dimensional electron gas. An optimal implantation dose can be reached so that the detector responsivity is maximized at zero gate voltage or with the gate floating. The relationship between the ion dosage and the threshold voltage, electron mobility, electron density, responsivity, and noise-equivalent power (NEP) is obtained. A minimum optical NEP of 47  W/Hz⎯⎯⎯⎯⎯√$47\hspace{0.17em}\hspace{0.17em}\mathrm{W}/\sqrt{\text{Hz}}$ is achieved from a two-terminal detector at 0.65 THz. The capability of two-terminal operation allows for the design of a large array of antenna-coupled high-electron-mobility transistor detectors without the demanding needs of routing negative gate voltage lines around the antenna array and minimizing the gate leakage current.

The authors acknowledge support from the National Key Research and Development Program of China (No. 2016YFF0100501), the China National Natural Science Foundation (Nos. 61771466 and 61775231), the Youth Innovation Promotion Association CAS (No. 2017372), the Six Talent Peaks Project of Jiangsu Province, China (No. XXRJ-079), and the Russian Foundation for Basic Research (No. 17-52-53063).

Abstract-Magnetic quantum ratchet effect in (Cd,Mn)Te- and CdTe-based quantum well structures with a lateral asymmetric superlattice

P. Faltermeier, G. V. Budkin, J. Unverzagt, S. Hubmann, A. Pfaller, V. V. Bel'kov, L. E. Golub, E. L. Ivchenko, Z. Adamus, G. Karczewski, T. Wojtowicz, V. V. Popov, D. V. Fateev, D. A. Kozlov, D. Weiss, S. D. Ganichev

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.155442

We report on the observation of magnetic quantum ratchet effect in (Cd,Mn)Te- and CdTe-based quantum well structures with an asymmetric lateral dual grating gate superlattice subjected to an external magnetic field applied normal to the quantum well plane. A dc electric current excited by cw terahertz laser radiation shows $1/B$ oscillations with an amplitude much larger as compared to the photocurrent at zero magnetic field. We show that the photocurrent is caused by the combined action of a spatially periodic in-plane potential and the spatially modulated radiation due to the near-field effects of light diffraction. Magnitude and direction of the photocurrent are determined by the degree of the lateral asymmetry controlled by the variation of voltages applied to the individual gates. The observed magneto-oscillations with enhanced photocurrent amplitude result from Landau quantization and, for (Cd,Mn)Te at low temperatures, from the exchange enhanced Zeeman splitting in diluted magnetic heterostructures. Theoretical analysis, considering the magnetic quantum ratchet effect in the framework of semiclassical approach, describes quite well the experimental results.

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Abstract-Giant cross-polarization conversion of terahertz radiation by plasmons in an active graphene metasurface

O. V. Polischuk1, V. S. Melnikova2 and V. V. Popov1,2,3
http://scitation.aip.org/content/aip/journal/apl/109/13/10.1063/1.4963276
1 Saratov Branch, Kotelnikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Saratov 410019, Russia
2 National Research Saratov State University, Saratov 410012, Russia
3 Saratov Scientific Center of the Russian Academy of Sciences, Saratov 410028, Russia
Appl. Phys. Lett. 109, 131101 (2016); http://dx.doi.org/10.1063/1.4963276

Results of theoretical investigation of the cross-polarization conversion of terahertz (THz) radiation by the graphene metasurface formed by a periodic array of graphene nanoribbons located at the surface of a high-refractive-index dielectric substrate are presented. Giant polarization conversion at the plasmonresonance frequencies takes place without applying external DC magnetic field. Pumping graphene by its direct optical illumination or diffusion pumping allows for compensating the Drude losses in grapheneand leads to further enhancement of the polarization conversion. It is shown that the total polarizationconversion can be achieved in the total internal reflection regime of THz wave from the graphenemetasurface at room temperature.

Abstract-Terahertz ratchet effects in graphene with a lateral superlattice

P. Olbrich, J. Kamann, M. König, J. Munzert, L. Tutsch, J. Eroms, D. Weiss, Ming-Hao Liu (劉明豪), L. E. Golub, E. L. Ivchenko, V. V. Popov, D. V. Fateev, K. V. Mashinsky, F. Fromm, Th. Seyller, and S. D. Ganichev

Phys. Rev. B 93, 075422 – Published 12 February 2016

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.93.075422

Experimental and theoretical studies on ratchet effects in graphene with a lateral superlattice excited by alternating electric fields of terahertz frequency range are presented. A lateral superlattice deposited on top of monolayer graphene is formed either by periodically repeated metal stripes having different widths and spacings or by interdigitated comblike dual-grating-gate (DGG) structures. We show that the ratchet photocurrent excited by terahertz radiation and sensitive to the radiation polarization state can be efficiently controlled by the back gate driving the system through the Dirac point as well as by the lateral asymmetry varied by applying unequal voltages to the DGG subgratings. The ratchet photocurrent includes the Seebeck thermoratchet effect as well as the effects of “linear” and “circular” ratchets, sensitive to the corresponding polarization of the driving electromagnetic force. The experimental data are analyzed for the electronic and plasmonic ratchets taking into account the calculated potential profile and the near field acting on carriers in graphene. We show that the photocurrent generation is based on a combined action of a spatially periodic in-plane potential and the spatially modulated light due to the near-field effects of the light diffraction.

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Abstract-Noncentrosymmetric plasmon modes and giant terahertz photocurrent in a two-dimensional plasmonic crystal

V. V. Popov, D. V. Fateev, E. L. Ivchenko, and S. D. Ganichev

Phys. Rev. B 91, 235436 – Published 19 June 2015

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.91.235436

We introduce and theoretically study the plasmon-photogalvanic effect in a planar noncentrosymmetric plasmonic crystal containing a homogeneous two-dimensional electron system gated by a periodic metal grating with an asymmetric unit cell. The plasmon-photogalvanic dc current arises due to the two-dimensional electron drag by the noncentrosymmetric plasmon modes excited under normal incidence of terahertz radiation. We show that the collective plasmon modes of the planar plasmonic crystal become strongly noncentrosymmetric in the weak-coupling regime of their anticrossing. A large plasmon wave vector (which is typically by two-three orders of magnitude greater than the terahertz photon wave vector) along with strong near-field enhancement at the plasmon resonance make the plasmonic drag a much stronger effect compared to the photon drag observed in conventional two-dimensional electron systems.

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Abstract-Noncentrosymmetric plasmon modes and giant terahertz photocurrent in a two-dimensional plasmonic crystal

V. V. Popov, D. V. Fateev, E. L. Ivchenko, S. D. Ganichev

http://xxx.tau.ac.il/abs/1505.06847

(Submitted on 26 May 2015)

We introduce and theoretically study the plasmon-photogalvanic effect in the planar noncentrosymmetric plasmonic crystal containing a homogeneous two-dimensional electron system gated by a periodic metal grating with an asymmetric unit cell. The plasmon-photogalvanic DC current arises due to the two-dimensional electron drag by the noncentrosymmetric plasmon modes excited under normal incidence of terahertz radiation. We show that the collective plasmon modes of the planar plasmonic crystal become strongly noncentrosymmetric in the weak coupling regime of their anticrossing. Large plasmon wavevector (which is typically by two-three orders of magnitude greater than the terahertz photon wavevector) along with strong near-field enhancement at the plasmon resonance make the plasmonic drag a much stronger effect compared to the photon drag observed in conventional two-dimensional electron systems.

Abstract-Current-driven detection of terahertz radiation using a dual-grating-gate plasmonic detector

S. Boubanga-Tombet^1,a), Y. Tanimoto¹, A. Satou¹, T. Suemitsu¹, Y. Wang²,H. Minamide², H. Ito², D. V. Fateev^3,4, V. V. Popov^3,4 and T. Otsuji¹
 HIDE AFFILIATIONS
1 Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-Ku, Sendai 980-8577, Japan
2 RIKEN Sendai, 519-1399 Aramaki Aoba, Aoba-ku, Sendai 980-0845, Japan
3 Kotelnikov Institute of Radio Engineering and Electronics (Saratov Branch), 410019 Saratov, Russia
4 Saratov State University, 410012 Saratov, Russia
a) Author to whom correspondence should be addressed. Electronic mail: stephanealbon@hotmail.com
Appl. Phys. Lett. 104, 262104 (2014); http://dx.doi.org/10.1063/1.4886763

We report on the detection of terahertz radiation by an on-chip planar asymmetric plasmonicstructure in the frequency region above one terahertz. The detector is based on a field-effect transistor that has a dual grating gate structure with an asymmetric unit cell, which provides a geometrical asymmetry within the structure. Biasing the detector with a dc source-to-drain current in the linear region of the current-voltage characteristic introduces an additional asymmetry (electrical asymmetry) that enhances the detector responsivity by more than one order of magnitude (by a factor of 20) as compared with the unbiased case due to the cooperative effect of the geometrical and electrical asymmetries. In addition to the responsivity enhancement, we report a relatively low noise equivalent power and a peculiar non-monotonic dependence of the responsivity on the frequency, which results from the multi-plasmonic-cavity structure of the device.

Abstract-Plasmonic terahertz lasing in an array of graphene nanocavities

V. V. Popov, O. V. Polischuk, A. R. Davoyan, V. Ryzhii, T. Otsuji, and M. S. Shur
http://prb.aps.org/abstract/PRB/v86/i19/e195437


.We propose a novel concept of terahertz lasing based on stimulated generation of plasmons in a planar array of graphene resonant micro/nanocavities strongly coupled to terahertz radiation. Due to the strong plasmon confinement and superradiant nature of terahertz emission by the array of plasmonic nanocavities, the amplification of terahertz waves is enhanced by many orders of magnitude at the plasmon resonance frequencies. We show that the lasing regime is ensured by the balance between the plasmon gain and plasmon radiative damping.