Source: http://web-ext.u-aizu.ac.jp/official/researchact/annual-review/2010/computerScience/cnl.html
Timestamp: 2019-04-19 16:51:55+00:00

Document:
The theory and computer modeling of graphene-based devices (field-effect transistors, lasers, etc.) - the basis of future carbon electronics.
Investigation of cardiac electrical activity utilizing high-performance computing systems.
Moscow Institute of Physics and Technology, and others.
I. Khmyrova, R. Yamase, M. Fukuda, and N.Watanabe. Analysis of terahertz plasma resonances in structures with two-dimensional electron systems periodicaslly modulated by interdigitated gate. J.Appl.Phys., 108:074511, 2010.
Simple analytical model is developed to evaluate spatial distribution of sheet electron density in the channel of the high-electron mobility (HEMT)-like structure periodically modulated by the bias voltages applied to interdigitated gate. Resonant frequencies of plasma oscillations excited in the two-dimensional electron gas (2DEG) channel of such structures are evaluated in the ideal and realistic situations. The realistic model accounts for the ungated regions which due to nonideality of gate contact 2DEG channel system can be also affected by the gate bias voltages. It is shown that plasma resonances in realistic structures with fringed ungated regions deviate from those predicted by the ideal model. The model developed can be used to interpret the terahertz plasmon spectra measured experimentally.
V. Ryzhii, M. Ryzhii, A .Satou, T. Otsuji, and V. Mitin. Analytical device model for graphene bilayer field-effect transistors using weak nonlocality approximation. Journal of Applied Physics, 109:064508 1-10, 2011.
We develop an analytical device model for graphene bilayer field-effect transistors (GBL-FETs) with the back and top gates. The model is based on the Boltzmann equation for the electron transport and the Poisson equation in the weak nonlocality approximation for the potential in the GBL-FET channel. The potential distributions in the GBL-FET channel are found analytically. The source-drain current in GBL-FETs and their transconductance are expressed in terms of the geometrical parameters and applied voltages by analytical formulas in the most important limiting cases. These formulas explicitly account for the short-gate effect and the effect of drain-induced barrier lowering. The parameters characterizing the strength of these effects are derived. It is shown that the GBL-FET transconductance exhibits a pronounced maximum as a function of the top-gate voltage swing. The interplay of the short-gate effect and the electron collisions results in a nonmonotonic dependence of the transconductance on the top-gate length.
M. Ryzhii, V. Ryzhii, T. Otsuji, V. Mitin, and M.S. Shur. Electrically induced n-i-p junctions in multiple graphene layer structures. Physical Review B, 82(7):075419 1-6, 2010.
The Fermi energies of electrons and holes and their densities in different graphene layers (GLs) in the n and p regions of the electrically induced n-i-p junctions formed in multiple-GL structures are calculated both numerically and using a simplified analytical model. The reverse current associated with the injection of minority carriers through the n and p regions in the electrically induced n-i-p junctions under the reverse bias is calculated as well. It is shown that in the electrically induced n-i-p junctions with moderate numbers of GLs the reverse current can be substantially suppressed. Hence, multiple-GL structures with such n-i-p junctions can be used in different electron and optoelectronic devices.
T. Otsuji, H. Karasawa, T. Watanabe, T. Suemitsu, M. Suemitsu, E. Sano, W. Knap, and V. Ryzhii. Emission of terahertz radiation from two-dimensional electron systemsnext term in previous termsemiconductor nano-heterostructures. Comptes Rendus Physique, 11(7-8):421-432, 2010.
This article reviews recent advances in previous termemission of terahertz radiation from two-dimensionalnext term (2D) previous termelectron systemsnext term in previous termsemiconductor nano-heterostructures.next term 2D plasmon resonance is first presented to demonstrate intense broadband previous termterahertz emissionnext term from InGaP/InGaAs/GaAs material previous termsystems.next term The device structure is based on a high-previous termelectronnext term mobility transistor and incorporates the author's original interdigitated dual-grating gates. The second topic focuses on graphene, a monolayer carbon-atomic honeycomb lattice crystal, exhibiting unique carrier transport and optical properties owing to the massless and gapless energy spectrum. Coherent stimulated previous termterahertz emissionnext term from femtosecond infrared-laser pumped epitaxial graphene is experimentally observed, reflecting the occurrence of negative dynamic conductivity and population inversion.
A.A. Dubinov, V.Ya. Aleshkin, V. Mitin, T. Otsuji, and V. Ryzhii. Terahertz surface plasmons in optically pumped graphene structures. Journal of Physics: Condensed Matter, 23(14):145302, 2011.
We analyze the surface plasmons (SPs) propagating along optically pumped singlegraphene layer (SGL) and multiple-graphene layer (MGL) structures. It is shown that at sufficiently strong optical pumping when the real part of the dynamic conductivity of SGL and MGL structures becomes negative in the terahertz (THz) range of frequencies due to the interband population inversion, the damping of the THz SPs can give way to their amplification. This effect can be used in graphene-based THz lasers and other devices. Due to the relatively small SP group velocity, the absolute value of their absorption coefficient (SP gain) can be large, substantially exceeding that of optically pumped structures with dielectric waveguides. A comparison of SGL and MGL structures shows that to maximize the SP gain the number of graphene layers should be properly chosen.
I. Khmyrova, R. Yamase, and N. Watanabe. Analysis of Plasma Resonances in Terahertz Devices with Grating Gate. In 35th International Conference on Infrared, Millimeter and THz Waves (IRMMW- THz 2010), pages MoP.85, Rome, Italy, Sept. 2010.
Analytical model is developed and used to calculate spatial distribution of sheet electron density in the channel of grid-grating gated HEMT structure and resonant frequencies of plasma waves excited in the channel. It is shown that increasing number of gates results in spectrum broadening.
N. Watanabe R. Yamase, M. Fukuda and I.Khmyrova. Tunable plasma resonances in Terahertz HEMT-based devices with interdigitated grating gate: Analytical model. In 2010 Asia-Pacific Radio Science Conference (AP-RASC'10), pages DP−5, Toyama, Japan, Sept. 2010.
In the paper we develop simple analytical model for evaluation of resonant frequencies of plasma waves propagating in the 2DEG channel periodically modulated by bias voltages applied to interdigitated grating gate.
I.Khmyrova. Equivalent circuit modeling of terahertz devices and resonant MEMS with two-dimensional electron gas system. In 15th IEEE Mediterranean Electrotechnical Conf., page 3135, Valletta, Malta, Apr. 2010.
Equivalent circuit models have been developed to study the performance of the devices with two-dimensional electron gas (2DEG) system for terahertz (THz) applications (grid-grating-gated high-electron-mobility transistor (HEMT)) and for sensing (multi-cantilever resonant sensor). The components of the equivalent circuits were related to physical and geometrical parameters of the devices under consideration. The developed equivalent circuits were used to simulate frequency performance of the devices under consideration invoking IsSpice circuit simulator.
I. Khmyrova, R. Yamase, and N. Watanabe. Model for evaluation of terahertz plasma resonances in HEMT-based devices with grating gate. In 8th Int. Conf. on Advabed Semicon. Devices and Microsystems (ASDAM 2010), pages 13-16, Smolenice Castle, Slovakia, Oct. 2010.
We propose simple analytical model for calculation of spatial distribution of the sheet electron density in the channel of high-electron mobility transistor (HEMT) periodically modulated by the bias voltage applied to grid-grating gate. The contribution of ungated regions of two-dimensional electron gas (2DEG) channel is taken into account. The developed model allows to evaluate resonant frequencies of plasma oscillations excited in such periodically modulated 2DEG channel. The proposed model can be useful in the interpretation of experimentally obtained data and optimization of the grating-gated HEMT-like structures for THz applications.
E. Ryzhii and M. Ryzhii. An algorithm of action potential duration distribution with 3D biventricular heart model. In 29th Progress in Electromagnetics Research Symposium (PIERS), Marrakesh, Morocco, March 2011. The Electromagnetics Academy.
In this study we investigate the influence of different configurations of midmyocardial layer allocation on the action potential duration (APD) and surface electrocardiogram (ECG). For this purpose we proposed an algorithm for APD spatial distribution and implemented it together with the combined ion-channel and 3D biventricular heart model to calculate body surface ECG. Our simulations demonstrated that the thickness of M-cell layer affected in maximal and minimal APD within ventricular wall and also reflected in T-wave amplitude and QT interval on ECG increasing with the thickness of midmyocardial layer.
V. Ryzhii, M. Ryzhii, T. Otsuji, A. Satou, A.A. Dubiniv, V. Mitin, and M.S. Shur. Graphene terahertz lasers and photodetectors. In Asia-Pacific Radio Science Conference (AP-RASC 2010), Toyama, Japan, September 2010. IUSI, IEICE.
We demonstrate that the THz/MIR lasers under consideration can surpass the quantum cascade lasers at the lower edge of the THz spectrum. The comparison of the multiple-GL THz/MIR photodetectors with photodetectors based on the standard narrow-gap materials as well as with those made of the standard semiconductor quantum heterostructures, in particular, quantum-well and quantum-dot photodetectors shows that the former can provide markedly higher responsivity and detectivity. The advantages of the proposed graphene photodetectors are associated with higher quantum efficiency and lower thermogeneration rate.
M. Ryzhii, T. Otsuji, V. Mitin, M.S. Shur, and V. Ryzhii. Field-effect in multiple graphene layer structures. In Int. Conference on Solid State Device and Materials (SSDM2010), Tokyo, Japan, September 2010. The Japan Society of Applied Physics.
We report the results of a theoretical investigation how the gate voltage affects the electron distribution over the graphene layers in gated multiple-graphene-layer structures.
V. Ryzhii, M. Ryzhii, N. Ryabova, V. Mitin, and T. Otsuji. Teraherts and infrared detectors based on graphene structures. In Quantum Structure Infrared Photodetector Conference (QSIP 2010), Istanbul, Turkey, August 2010. NASA, JPL, AFRL.
We consider newly proposed terahertz and infrared interband detectors based on multiple-graphene-layer structures with p-i-n junctions. Using the developed device model, we calculate the photodetector characteristics (responsivity and dark current limited detectivity) and compare them with the characteristics of other photodetectors. It is shown that due to relatively high quantum efficiency and weakened thermogeneration processes, the detectors under consideration can exhibit superior performance.
H. Karasawa, T. Watanabe, T. Otsuji, M. Ryzhii, A. Satou, and V. Ryzhii. Observation of amplified stimulated terahertz emission in optically pumped epitaxial graphene heterostructures. In CLEO: Conference on Lasers and Electrooptics Digest, San Jose, USA, May 2010. APS, IEEE, OSA.
We experimentally observed an amplified stimulated terahertz emission from an epitaxial graphene-on-silicon heterostructure. The result well supports the occurrence of negative dynamic conductivity leading to a new type of terahertz lasers.
V. Ryzhii, M. Ryzhii, N. Ryabova, T. Otsuji, V.Ya. Aleshkin, A.A. Dubinov, V. Mitin, and M.S. Shur. Concepts of novel terahertz and mid-infrared photodetectors and lasers based on multiple-graphene layer structures. In XXI Int. Conference on Photoelectronics and Night Vision Devices, Moscow, Russia, May 2010. SPIE.
The multiple-graphene-layer THz/MIR photodetectors are compared with photodetectors made of the standard narrow-gap materials as well as with those based on the standard semiconductor quantum heterostructures, in particular, quantum-well and quantum-dot photodetectors. The advantages of the proposed photodetectors are associated with higher quantum efficiency and lower thermogeneration rate. The lasers under consideration can surpass the quantum cascade lasers at the lower edge of the THz spectrum.
V. Ryzhii, M. Ryzhii, A.A. Dubinov, T. Otsuji, M.S. Shur, and V. Mitin. Novel terahertz and infrared devices on multiple graphene structures: concepts and characteristics. In VCIAN: Villa Conference on Interactions Among Nanostructures, Santorini, Greece, June 2010.
Unique spectral properties of graphene layers (GLs) associated with their gapless energy spectrum open up prospects in creating of novel terahertz (THz) and infrared (IR) lasers and photodetectors. The utilization of stacks of disoriented perfect GLs in such multiple-GL devices can result in significantly higher performance in comparison with single-GL devices. In this paper, we overview the concepts of novel THz and IR devices utilizing multiple-GL structures. Using the developed device models, we calculated the characteristics and demonstrated that these devices, THz and IR lasers and photodetectors, can substantially surpass analogous devices made of standard quantum structures, in particular, multiple quantum-well and quantumdot structures.
M. Ryzhii, T. Otsuji, V. Mitin, and V. Ryzhii. Characteristics of p-i-n terahertz and infrared photodiodes based on multiple graphene layer structures. In Int. Symposium on Graphene Devices: Technology, Physics, and Modeling (ISGD 2010), Sendai, Japan, October 2010. JST-CREST, RIEC.
We compare the multiple-graphene-layer photodiodes (MGL-PD) characteristics with those of the field-effect phototransistors based on graphene bilayers proposed earlier and other THz and IR detectors. As demonstrated, MGL-PDs appears to have considerable promise as high-temperature wideband (or multicolor) THz and IR detectors.
M. Ryzhii, V. Ryzhii, T. Otsuji, and V. Mitin. Terahertz and infrared detectors based on multiple-graphene layers with p-i-n junctions: device model and characteristics. In 29th Progress in Electromagnetics Research Symposium (PIERS), Marrakesh, Morocco, March 2011. The Electromagnetics Academy.
Using developed model, we obtain analytical formulas for the multiple-graphenelayer photodiodes (MGL-PDs) responsivity and dark-current limited detectivity and compare the MGL-PD characteristics with those of the field-effect phototransistors based on graphene bilayers (GBL-PTs) proposed earlier. We demonstrate that at lower temperatures, GBL-PT can surpass MGL-PDs exhibiting huge values of the responsivity and detectivity. We also show that MGL-PDs can overperform other THz and IR detectors, particularly, at elevated (room) temperatures.
A.Satou, T. Otsuji, and V. Ryzhii. Theoretical study of population inversion in graphene under pulse excitation. In Int. Symposium on Graphene Devices: Technology, Physics, and Modeling (ISGD 2010), Sendai, Japan, October 2010. JST-CREST, RIEC.
We study theoretically the population inversion in intrinsic graphene under optical pulse excitation at room temperature. We develop the theoretical model of carrier relaxation dynamics based on the rate equations derived from the quasi-classical Boltzmann equation. We take into account the energy relaxation and recombination by the intra and interband optical phonon (OP) scattering, and we assume that the carrier-carrier (CC) scattering is dominant so that the carrier distribution is always the quasi-Fermi distribution. Using the model developed, we demonstrate that the population inversion can be achieved under the pulse excitation even in the limiting case of the dominant CC scattering.
D. Svintsov, V. Vyurkov, V. Ryzhii, and T. Otsuji. Effect of 'mexican hat' on graphene bilayer field-effect transistor characteristics. In Int. Symposium on Graphene Devices: Technology, Physics, and Modeling (ISGD 2010), Sendai, Japan, October 2010. JST-CREST, RIEC.
Ballistic model of a graphene bilayer field-effect transistor (GBL FET) was developed. It incorporates the exact graphene bilayer electronic spectrum reminding a 'Mexican hat'. The isotropic minimum shifted from the center of a band results in a conductance step at low temperature which was so far known for one-dimensional conductors due to conductance quantization. At room temperature a GBL FET exhibits an extremely high transconductance in ON-state. It makes a GBL FET promising for high-frequency analog circuits. We also point out to possibility of electron localization inside the channel on the top of potential barrier.
T. Otsuji, S.A. Boubanga Tombet, S. Chan, T. Watanabe, A. Satou, and V. Ryzhii. Terahertz light amplification by stimulated emission of radiation from optically pumped graphene. In 29th Progress in Electromagnetics Research Symposium (PIERS), Marrakesh, Morocco, March 2011. The Electromagnetics Academy.
The gapless and linear energy spectra of electrons and holes in graphene lead to nontrivial features such as negative dynamic conductivity in the terahertz spectral range. This paper reviews the recent advances in theoretical and experimental study on terahertz light amplification by stimulated emission of radiation in optically pumped graphene.
S. Boubanga Tombet, S. Chan, A. Satou, T. Watanabe, V. Ryzhii, and T. Otsuji. Amplified stimulated terahertz emission at room temperature from optically pumped graphene. In EOS Annual Meeting, Paris, France, October 2010. EOS.
Y. Takatsuka, E. Sano, V. Ryzhii, and T. Otsuji. THz amplifiers based on multilayer graphene and field-enhancement structures. In Int. Symposium on Graphene Devices: Technology, Physics, and Modeling (ISGD 2010), Sendai, Japan, October 2010. JST-CREST, RIEC.
Terahertz (THz) devices have been developed over the last decade to utilize THz waves for non-destructive sensing and high-speed wireless communications. Ryzhii et al. theoretically demonstrated the feasibility of THz lasing in optically pumped multiple graphene layer (MGL) structures and proposed THz laser structures. In addition, metallic sheets perforated with a periodic array of holes (metal mesh) have been used for band-pass filters with resonant transmittance of unity. In these periodic structures, induced surface plasmon polaritons (SPPs) enhance the electric field near the holes. We investigated THz amplifiers composed of MGL and metal mesh structures using finite difference time domain (FDTD) electromagnetic simulation. A remarkable increase in the transmittance for the metal mesh structure with MGL was observed.
A. Satou, T. Otsuji, and V. Ryzhii. Study of hot carriers in optically pumped graphene. In Int. Conference on Solid State Device and Materials (SSDM2010), pages 882-883, Tokyo, Japan, September 2010. The Japan Society of Applied Physics.
T. Otsuji, M. Suemitsu, E. Sano, and V. Ryzhii. Trends and future for graphene-based terahertz nano-photonics. In ISTESNE: Int. Symposium on Technology Evolution for Silicon Nano-Electronics, Tokyo, Japan, June 2010. The Japan Society of Applied Physics.
T. Otsuji, S. Chan, S.-A. Boubanga-Tombet, H. Karasawa, T. Watanabe, A. Satou, H. Fukidome, M. Suemitsu, and V. Ryzhii. Observation of amplified stimulated terahertz emission from heteroepitaxial graphene-onsilicon materials. In WINDS: Workshop on Innovative Devices and Systems, Hawaii, USA, December 2010.
M. Ryzhii. Co-investigator on the project 'Terahertz plasma wave nanoelectronic devices' supported by the Grant-in-Aid for Scientific Research (S) from the Japanese Society for Promotion of Science, 2006-2011.
M. Ryzhii. Co-investigator on the project 'Development of Graphene on Silicon (GOS) device modeling technology' supported by Japan Science and Technology Agency, CREST, 2007-2012.
M. Ryzhii. Co-investigator on the project supported by Nation-wide Research Grant from RIEC, 2010-2011.
V. Ryzhii. Nation-wide Research Grant from RIEC, 2010-2011.

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