V. G. Leiman

Effect of plasma resonances on dynamic characteristics of double graphene-layer optical modulator

We analyze the dynamic operation of an optical modulator based on double graphene-layer (GL) structure utilizing the variation of the GL absorption due to the electrically controlled Pauli blocking effect. The developed device model yields the dependences of the modulation depth on the control voltage and the modulation frequency. The excitation of plasma oscillations in double-GL structure can result in the resonant increase of the modulation depth, when the modulation frequency approaches the plasma frequency, which corresponds to the terahertz frequency for the typical parameter values.

Analysis of resonant detection of terahertz radiation in high-electron mobility transistor with a nanostring/carbon nanotube as the mechanically floating gate

We develop a device model for a resonant detector of electromagnetic radiation with a frequency in the terahertz (THz) range modulated by megahertz (MHz) or gigahertz (GHz) signals based on a micromachined high-electron mobility transistor (HEMT) with a metallized nanostring (NS) or metallic carbon nanotube (CNT) as mechanically the floating gate and analyze the detector operation. The device model describes both the NS/CNT mechanical motion and plasma effects in the HEMT two-dimensional electron channel. Using this model, we calculate the output gate alternating current and the detector responsivity as functions of the carrier (in the THz range) and modulation frequencies, which are in the THz and MHz (or GHz range), respectively. It is shown that the THz detector responsivity exhibits sharp and high maxima under the conditions of both mechanical and plasma resonances.

Backward waves in planar insulator?metal?insulator waveguide structures

Existence conditions of backward waves and waves with zero group velocity in insulator–metal–insulator (IMI) structures are obtained and expressions for the group velocity of the surface plasmon polariton (SPP) are derived. We consider the general case when the two insulator half-spaces may be identical or different. The effect of losses on dispersion curves and values of the energy velocity is analyzed. The obtained equations are used for a characterization and a detailed study of backward waves in thin silver film waveguides.

Double injection, resonant-tunneling recombination, and current-voltage characteristics in double-graphene-layer structures

We evaluate the effect of the recombination associated with interlayer transitions in ungated and gated double-graphene-layer (GL) structures on the injection of electrons and holes. Using the proposed model, we derive analytical expressions for the spatial distributions of the electron and hole Fermi energies and the energy gap between the Dirac points in GLs as well as their dependences on the bias and gate voltages. The current-voltage characteristics are calculated as well. The model is based on hydrodynamic equations for the electron and hole transports in GLs under the self-consistent electric field. It is shown that in undoped double-GL structures with weak scattering of electrons and holes on disorder, the Fermi energies and the energy gap are virtually constant across the main portions of GLs, although their values strongly depend on the voltages and recombination parameters. In contrast, the electron and hole scattering on disorder lead to substantial nonuniformities. The resonant inter-GL tunne...

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.

Detection of Modulated Terahertz Radiation Using Combined Plasma and Mechanical Resonances in Double-Carbon-Nanotube Device

We propose a resonant detector of terahertz radiation modulated by megahertz or gigahertz signals. The detector is based on mechanically floating carbon nanotubes (CNTs), suspended over an insulator. The device operation is associated with the excitation of both plasma and mechanical oscillations in CNTs resulting in an ac displacement current between them. This current plays the role of the detector output signal. Using the proposed device model, we find that the frequency dependence of the detector responsivity exhibits a sharp peak at the combined plasma-mechanical resonance and estimate its maximum value.

Parametric instability in a nanoelectromechanical detector of modulated terahertz radiation on the basis of a high electron mobility transistor with a mobile elastic gate

Parametric instability in a modulated terahertz radiation detector based on a high electron mobility transistor with a mobile elastic gate fabricated from a conductor in the form of a micronanocantilever is studied in detail. The analysis is based on the method of coupled oscillations and subsequent testing by direct numerical integration of the original equations. The thresholds and increments of the instability are determined. The feasibility of practical realization of conditions for parametric instability in such detectors is discussed.

Infrared photodetectors based on graphene van der Waals heterostructures

V Ryzhii, M Ryzhii, D Svintsov, V Leiman, V Mitin, M S Shur and T Otsuji 1 Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577, Japan 2 Institute of Ultra High Frequency Semiconductor Electronics of RAS, Moscow 117105, Russia 3 Center for Photonics and Infrared Engineering, Bauman Moscow State Technical University, Moscow 111005, Russia 4 Department of Computer Science and Engineering, University of Aizu, Aizu-Wakamatsu 965-8580, Japan 5 Laboratory of 2D Materials’ Optoelectronics, Moscow Institute of Physics and Technology, Dolgoprudny 141700, Russia 6 Department of Electrical Engineering, University at Buffalo, Buffalo, New York 1460-1920, USA 7 Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA

Two-dimensional plasmons in lateral carbon nanotube network structures and their effect on the terahertz radiation detection

We consider the carrier transport and plasmonic phenomena in the lateral carbon nanotube (CNT) networks forming the device channel with asymmetric electrodes. One electrode is the Ohmic contact to the CNT network and the other contact is the Schottky contact. These structures can serve as detectors of the terahertz (THz) radiation. We develop the device model for collective response of the lateral CNT networks which comprise a mixture of randomly oriented semiconductor CNTs (s-CNTs) and quasi-metal CNTs (m-CNTs). The proposed model includes the concept of the collective two-dimensional (2D) plasmons in relatively dense networks of randomly oriented CNTs (CNT “felt”) and predicts the detector responsivity spectral characteristics exhibiting sharp resonant peaks at the signal frequencies corresponding to the 2D plasmonic resonances. The detection mechanism is the rectification of the ac current due the nonlinearity of the Schottky contact current-voltage characteristics under the conditions of a strong enhancement of the potential drop at this contact associated with the plasmon excitation. The detector responsivity depends on the fractions of the s- and m-CNTs. The burning of the near-contact regions of the m-CNTs or destruction of these CNTs leads to a marked increase in the responsivity in agreement with our experimental data. The resonant THz detectors with sufficiently dense lateral CNT networks can compete and surpass other THz detectors using plasmonic effects at room temperatures.

Graphene nanoelectromechanical resonators for the detection of modulated terahertz radiation

We propose and analyze the detector of modulated terahertz (THz) radiation based on the graphene field-effect transistor with mechanically floating gate made of graphene as well. The THz component of incoming radiation induces resonant excitation of plasma oscillations in graphene layers (GLs). The rectified component of the ponderomotive force between GLs invokes resonant mechanical swinging of top GL, resulting in the drain current oscillations. To estimate the device responsivity, we solve the hydrodynamic equations for the electrons and holes in graphene governing the plasma-wave response, and the equation describing the graphene membrane oscillations. The combined plasma-mechanical resonance raises the current amplitude by up to four orders of magnitude. The use of graphene as a material for the elastic gate and conductive channel allows the voltage tuning of both resonant frequencies in a wide range.