Dmitry Svintsov

Hydrodynamic model for electron-hole plasma in graphene

We propose a hydrodynamic model describing steady-state and dynamic electron and hole transport properties of graphene structures which accounts for the features of the electron and hole spectra. It is intended for electron-hole plasma in graphene characterized by high rate of inter-carrier scattering compared to external scattering (on phonons and impurities), i.e., for intrinsic or optically pumped (bipolar plasma), and gated graphene (virtually monopolar plasma). We demonstrate that the effect of strong interaction of electrons and holes on their transport can be treated as a viscous friction between the electron and hole components. We apply the developed model for the calculations of the graphene dc conductivity; in particular, the effect of mutual drag of electrons and holes is described. The spectra and damping of collective excitations in graphene in the bipolar and monopolar limits are found. It is shown that at high gate voltages and, hence, at high electron and low hole densities (or vice-versa...

Voltage-controlled surface plasmon-polaritons in double graphene layer structures

The spectra and damping of surface plasmon-polaritons (SPPs) in double graphene layer structures are studied. It is proved that SPPs in those structures exhibit an outstanding voltage tunability of velocity and damping, inherent to gated graphene, and a pronounced low-frequency coupling with photons inherent to non-gated structures. It is also shown that the spatial dispersion of conductivity significantly augments the free path and cutoff frequency of SPPs, which is of great importance for practical applications.

Double injection in graphene p-i-n structures

We study the processes of the electron and hole injection (double injection) into the i-region of graphene-layer and multiple graphene-layer p-i-n structures at the forward bias voltages. The hydrodynamic equations governing the electron and hole transport in graphene coupled with the two-dimensional Poisson equation are employed. Using analytical and numerical solutions of the equations of the model, we calculate the band edge profile, the spatial distributions of the quasi-Fermi energies, carrier density and velocity, and the current-voltage characteristics. In particular, we demonstrated that the electron and hole collisions can strongly affect these distributions. The obtained results can be used for the realization and optimization of graphene-based injection terahertz and infrared lasers.

Tunnel field-effect transistors with graphene channels

The lack of an OFF-state has been the main obstacle to the application of graphene-based transistors in digital circuits. Recently vertical graphene tunnel field-effect transistors with a low OFF-state current have been reported; however, they exhibited a relatively weak effect of gate voltage on channel conductivity. We propose a novel lateral tunnel graphene transistor with the channel conductivity effectively controlled by the gate voltage and the subthreshold slope approaching the thermionic limit. The proposed transistor has a semiconductor (dielectric) tunnel gap in the channel operated by gate and exhibits both high ON-state current inherent to graphene channels and low OFF-state current inherent to semiconductor channels.

Graphene vertical cascade interband terahertz and infrared photodetectors

We propose and evaluate the vertical cascade terahertz and infrared photodetectors based on multiple-graphene-layer (GL) structures with thin tunnel barrier layers (made of tungsten disulfide or related materials). The photodetector operation is associated with the cascaded radiative electron transitions from the valence band in GLs to the conduction band in the neighboring GLs (interband- and inter-GL transitions). We calculate the spectral dependences of the responsivity and detectivity for the vertical cascade interband GL- photodetectors (I-GLPDs) with different number of GLs and doping levels at different bias voltages in a wide temperature range. We show the possibility of an effective manipulation of the spectral characteristics by the applied voltage. The spectral characteristics depend also on the GL doping level that opens up the prospects of using I-GLPDs in the multi-color systems. The advantages of I-GLPDs under consideration are associated with their sensitivity to the normal incident radiation, weak temperature dependence of the dark current as well as high speed of operation. The comparison of the proposed I-GLDs with the quantum-well intersubband photodectors demonstrates the superiority of the former, including a better detectivity at room temperature and a higher speed. The vertical cascade I-GLDs can also surpass the lateral p-i-n GLDs in speed.

Hydrodynamic electron transport and nonlinear waves in graphene

We derive the system of hydrodynamic equations governing the collective motion of massless fermions in graphene. The obtained equations demonstrate the lack of Galilean and Lorentz invariance and contain a variety of nonlinear terms due to the quasirelativistic nature of carriers. Using these equations, we show the possibility of soliton formation in an electron plasma of gated graphene. The quasirelativistic effects set an upper limit for soliton amplitude, which marks graphene out of conventional semiconductors. The mentioned noninvariance of the equations is revealed in spectra of plasma waves in the presence of steady flow, which no longer obey the Doppler shift. The feasibility of plasma-wave excitation by direct current in graphene channels is also discussed.

Carrier-carrier scattering and negative dynamic conductivity in pumped graphene

We theoretically examine the effect of carrier-carrier scattering processes on the intraband radiation absorption and their contribution to the net dynamic conductivity in optically or electrically pumped graphene. We demonstrate that the radiation absorption assisted by the carrier-carrier scattering is comparable with Drude absorption due to impurity scattering and is even stronger in sufficiently clean samples. Since the intraband absorption of radiation effectively competes with its interband amplification, this can substantially affect the conditions of the negative dynamic conductivity in the pumped graphene and, hence, the interband terahertz and infrared lasing. We find the threshold values of the frequency and quasi-Fermi energy of nonequilibrium carriers corresponding to the onset of negative dynamic conductivity. The obtained results show that the effect of carrier-carrier scattering shifts the threshold frequency of the radiation amplification in pumped graphene to higher values. In particular, the negative dynamic conductivity is attainable at the frequencies above 6 THz in graphene on SiO2 substrates at room temperature. The threshold frequency can be decreased to markedly lower values in graphene structures with high-κ substrates due to screening of the carrier-carrier scattering, particularly at lower temperatures.

Plasmons in tunnel-coupled graphene layers: backward waves with quantum cascade gain

We theoretically demonstrate that graphene-insulator-graphene tunnel structures can serve as plasmonic gain media due to the possibility of stimulated electron tunneling accompanied by emission of plasmons under application of interlayer voltage. The probability of plasmon-assisted tunneling is resonantly large at certain values of frequency and interlayer voltage corresponding to the transitions between chiral electron states with collinear momenta, which is a feature unique to the linear bands of graphene. The plasmon dispersion develops an anticrossing with the resonances in tunnel conductivity and demonstrates negative group velocity in several frequency ranges.D. Svintsov, Zh. Devizorova, T. Otsuji, and V. Ryzhii Laboratory of Nanooptics and Plasmonics, Moscow Institute of Physics and Technology, Dolgoprudny 141700, Russia Department of Physical and Quantum Electronics, Moscow Institute of Physics and Technology, Dolgoprudny 141700, Russia Kotelnikov Institute of Radio Engineering and Electronics, Russian Academy of Science, Moscow, 125009 Russia and Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577, Japan∗

Full loss compensation in hybrid plasmonic waveguides under electrical pumping

Surface plasmon polaritons (SPPs) give an opportunity to break the diffraction limit and design nanoscale optical components, however their practical implementation is hindered by high ohmic losses in a metal. Here, we propose a novel approach for efficient SPP amplification under electrical pumping in a deep-subwavelength metal-insulator-semiconductor waveguiding geometry and numerically demonstrate full compensation for the SPP propagation losses in the infrared at an exceptionally low pump current density of 0.8 kA/cm2. This value is an order of magnitude lower than in the previous studies owing to the thin insulator layer between a metal and a semiconductor, which allows injection of minority carriers and blocks majority carriers reducing the leakage current to nearly zero. The presented results provide insight into lossless SPP guiding and development of future high dense nanophotonic and optoelectronic circuits.

Nonlinear response of infrared photodetectors based on van der Waals heterostructures with graphene layers

We report on the device model for the infrared photodetectors based on the van der Waals (vdW) heterostructures with the radiation absorbing graphene layers (GLs). These devices rely on the electron interband photoexcitation from the valence band of the GLs to the continuum states in the conduction band of the inter-GL barrier layers. We calculate the photocurrent and the GL infrared photodetector (GLIP) responsivity at weak and strong intensities of the incident radiation and conclude that the GLIPs can surpass or compete with the existing infrared and terahertz photodetectors. The obtained results can be useful for the GLIP design and optimization.