Computational Nanoelectronics Laboratory

Victor I. Ryzhii Professor	Irina I. Khmyrova Associate Professor	Maxim V. Ryzhii Associate Professor	Alexander Dubinov Visiting Researcher

The research activity of the Computational Nano-Electronics Laboratory is focused on theoretical studies and computer modeling of physical processes in semiconductor microand nanostructures and in novel electronic and optoelectronic classical and quantum devices based on such structures. Since the laboratory establishment in 1993, its members have published more than 190 journal articles and made more than 200 presentations at international conferences. One of the members of the laboratory is a Fellow of the Institute of Electrical and Electronics Engineers (IEEE), Fellow of the American Physical Society, and Corresponding member of the Russian (national) Academy of Sciences. Two professors are the IEEE Senior Members. The research efforts of the laboratory members are now centered on theory and computer modeling of: The theory and computer modeling of graphene-based devices - the basis of future Carbon electronics. Semiconductor classical and quantum heterostructure devices operating in the terahertz range of frequencies (terahertz detectors, mixers, generators, and photomixers). Quantum-well and quantum-dot infrared photodetectors and other functional devices. Investigation of heart and brain electrical activity utilizing high-performance computing systems. Original research results obtained in this academic year have been published in refereed journal papers (published in Physical Review B, Journal of Applied Physics, Applied Physics Letters, Japanese Journal of Applied Physics, and others) and presented at different international conferences. The Computational Nano-Electronics Laboratory conducts research in cooperation with leading research groups at: Tohoku University (Sendai, Japan), Rensselaer Polytechnic Institute (Troy, USA), Institute for Physics of Microstructures RAS (Nizhny Novgorod, Russia), University at Buffalo (Buffalo, USA), Moscow Institute of Physics and Technology, Ioffe Physical-Technical Institute (St. Petersburg, Russia), Gothenburg University (Gothenburg, Sweden), and others.

Refereed Journal Papers

[m-ryzhii-01:2009, v-ryzhii-01:2009]	V. Ryzhii, M. Ryzhii, V. Mitin, and T. Otsuji. Terahertz and infrared photodetection using p-i-n multiple-graphene-layer structures. Journal of Applied Physics, 107(5):054512(7), 2010.
	We propose to utilize multiple-graphene-layer structures with lateral p-i-n junctions for terahertz and infrared (IR) photodetection and substantiate the operation of photodetectors based on these structures. Using the developed device model, we calculate the detector dc responsivity and detectivity as functions of the number of graphene layers and geometrical parameters and show that the dc responsivity and detectivity can be fairly large, particularly, at the lower end of the terahertz range at room temperatures. Due to relatively high quantum efficiency and low thermogeneration rate, the photodetectors under consideration can substantially surpass other terahertz and IR detectors. Calculations of the detector responsivity as a function of modulation frequency of THz and IR radiation demonstrate that the proposed photodetectors are very fast and can operate at the modulation frequency of several tens of gigahertz.
[m-ryzhii-02:2009, v-ryzhii-02:2009]	V. Ryzhii, M. Ryzhii, A. Satou, T. Otsuji, A. A. Dubinov, and V.Ya. Aleshkin. Feasibility of terahertz lasing in optically pumped epitaxial multiple graphene layer structures. Journal of Applied Physics, 106(8):084507(6), 2009.
	A multiple graphene layer (MGL) structure with a stack of GLs and a highly conducting bottom GL on SiC substrate pumped by optical radiation is considered as an active region of terahertz and far infrared lasers with external metal mirrors. The dynamic conductivity of the MGL structure is calculated as a function of the signal frequency, the number of GLs, and the optical pumping intensity. The utilization of optically pumped MGL structures might provide the achievement of lasing with the frequencies of about 1 THz at room temperature due to a high efficiency of pumping.
[m-ryzhii-03:2009, v-ryzhii-03:2009]	A.A. Dubinov, V.Ya. Aleshkin, M. Ryzhii, T. Otsuji, and V. Ryzhii. Terahertz laser with optically pumped graphene layers and Fabri-Perot resonator. Applied Physics Express, 2(9):092301(3), 2009.
	We propose and substantiate the concept of terahertz (THz) laser based on the optically pumped graphene layers and the resonant cavity of the Fabri-Perot type. The pumping scheme which corresponds to the optical interband excitation of graphene followed by the emission of an optical phonons cascade provides the population inversion for the interband transitions in a relatively wide range of THz frequencies. We demonstrate that the THz lasing in the device under consideration at room temperatures is feasible if its structure is optimized. The frequency and output power of the generated THz radiation can be tuned by varying the distance between the mirrors.
[m-ryzhii-04:2009,v-ryzhii-04:2009]	V. Ryzhii and M. Ryzhii. Graphene bilayer fieldeffect phototransistor for terahertz and infrared detection. Physical Review B, 79(24):245311(8), 2009.
	A graphene bilayer phototransistor (GBL-PT) is proposed and analyzed. The GBLPT under consideration has the structure of a field-effect transistor with a GBL as the channel sandwiched between the back and the top gates. The positive bias of the back gate creates the conducting source and drain sections in the channel, while the negatively biased top gate provides the potential barrier which is controlled by the charge of the photogenerated holes. The features of the GBL-PT operation are associated with the variation in both the potential distribution and the energy gap in different sections of the channel when the gate voltages change. Using the developed GBL-PT device model, the spectral characteristics, dark current, responsivity, photoelectric gain, and detectivity are calculated as functions of the applied voltages, energy of incident photons, intensity of electron and hole scattering, and geometrical parameters. It is shown that the GBL-PT spectral characteristics are voltage tuned. The GBL-PT performance as a photodetector in the terahertz and infrared regions of the spectrum can markedly exceed the performance of other photodetectors.
[m-ryzhii-05:2009, v-ryzhii-05:2009]	V. Ryzhii, M. Ryzhii, N. Ryabova, V. Mitin, and T. Otsuji. Graphene nanoribbon phototransistor: proposal and analysis. Japanese Journal of Applied Physics, 48(2):04C144(5), 2009.
	We propose and analyze a graphene tunneling transit time device based on a heterostructure with a lateral p-i-n junction electrically induced in the graphene layer by the applied gate voltages of different polarity. The depleted i-section of the graphene layer (between the gates) serves as both the tunneling injector and the transit region. Using the developed device model, we demonstrate that the ballistic transit of electrons and holes generated due to interband tunneling in the i-section results in the negative ac conductance in the terahertz frequency range, so that the device can serve as a terahertz oscillator.
[m-ryzhii-04:2008, v-ryzhii-04:2008]	V. Ryzhii, M. Ryzhii, N. Ryabova, V. Mitin, and T. Otsuji. Graphene nanoribbon phototransistor: proposal and analysis. Jpn. J. Appl. Phys., 48:04C144 (5), 2009.
	We consider a concept of a graphene nanoribbon phototransistor (GNR-PT) based on an array of GNRs operating as a photodetector of far-infrared (FIR) and terahertz (THz) radiation. The photodetector has the structure of a GNR field effect transistor with the back and relatively short top gates. To calculate the GNR-PT characteristics, we develop an analytical model of the device. This model generalizes the model we proposed previously by accounting for the possibility of not only the thermionic regime but also the tunneling regime of the GNR-PT operation. Using the developed model, we derive analytical formulas for the source-drain current as a function of the intensity and frequency of the incident radiation and bias voltages, and estimate the detector responsivity. The obtained formulas can be used for detector optimization by varying the dark current, photoelectric current gain, and voltage control of the spectral properties. The dependences of the absorption edge on GNR width and bias voltages can be utilized for the development of multicolor voltage tunable FIR/THz photodetectors.
[m-ryzhii-06:2009]	E. Ryzhii, M. Ryzhii, and D. Wei. A study of spatial action potential distributions in myocardium with 3D whole-heart model. Journal of Communications Technology and Electronics, page (accepted for publication), 2010.
	Computer simulations of cardiac electrical activity are conducted using a 3D wholeheart model incorporating ion-channel action potential formulations. An inhomogeneous continuous spatial distribution of action potentials based on different dependences of maximal slow delayed rectifier current conductance is proposed and implemented to study electrocardiographic T-waves. It is demonstrated that the proposed distribution is reasonable to reproduce realistic electrocardiographic waveforms.
[m-ryzhii-07:2009, v-ryzhii-06-2009]	V. Ryzhii, M. Ryzhii, A. Satou, T. Otsuji, and N. Kirova. Device model for graphene bilayer field-effect transistor. Journal of Applied Physics, 105(10):104510(9), 2009.
	We present an analytical device model for a graphene bilayer field-effect transistor (GBL-FET) with a graphene bilayer as a channel and with back and top gates. The model accounts for the dependences of the electron and hole Fermi energies as well as energy gap in different sections of the channel on the bias back-gate and top-gate voltages. Using this model, we calculate the dc and ac source-drain currents and the transconductance of GBL-FETs with both ballistic and collision dominated electron transport as functions of structural parameters, the bias backgate and top-gate voltages, and the signal frequency. It is shown that there are two threshold voltages, so that the dc current versus the top-gate voltage relation markedly changes depending on whether the section of the channel beneath the top gate (gated section) is filled with electrons, depleted, or filled with holes. The electron scattering leads to a decrease in the dc and ac currents and transconductances, whereas it weakly affects the threshold frequency. As demonstrated, the transient recharging of the gated section by holes can pronouncedly influence the ac transconductance resulting in its nonmonotonic frequency dependence with a maximum at fairly high frequencies.
[m-ryzhii-08:2009, v-ryzhii-07:2007]	V. Ryzhii, M. Ryzhii, M.S.Shur, and V. Mitin. Negative terahertz dynamic conductivity in electrically induced lateral p-i-n junction in graphene. Physica E, 42(4):719 E21, 2009.
	We analyze a graphene tunneling transit-time device based on a heterostructure with a lateral p-i-n junction electrically induced in the graphene layer and calculate its ac characteristics. Using the developed device model, it is shown that the ballistic transit of electrons and holes generated due to interband tunneling in the i-section results in the negative ac conductance in the terahertz frequency range. The device can serve as an active element of terahertz oscillators. quantum efficiency and low thermogeneration rate, the photodetectors under.
[v-ryzhii-08:2009]	V. Ryzhii, A. Dubinov, T. Otsuji, V. Mitin, and M.S. Shur. Terahertz lasers based on optically pumped multiple graphene structures with slot-line and dielectric waveguides. Journal of Applied Physics, 107(5):054505(5), 2010.
	Terahertz (THz) lasers on optically pumped multiple-graphene-layer (MGL) structures as their active region are proposed and evaluated. The developed device model accounts for the interband and intraband transitions in the degenerate electron-hole plasma generated by optical radiation in the MGL structure and the losses in the slot or dielectric waveguide. The THz laser gain and the conditions of THz lasing are found. It is shown that the lasers under consideration can operate at frequencies about 1 THz at room temperatures.
[v-ryzhii-09:2009]	V.V. Popov, T.Yu. Bagaeva, T. Otsuji, and V. Ryzhii. Oblique terahertz plasmons in graphene nanoribbon arrays. Physical Review B, 81(7):073404(4), 2009.
	We show that the plasmon frequencies in a one-dimensional dense array of doped (or gated) graphene nanoribbons can be changed through the entire terahertz range depending on the angle between the plasmon wave vector and the nanoribbon direction. The overdamped regime for oblique plasmons in the graphene nanoribbon array is discussed.
[v-ryzhii-10:2009]	A.V. Arsenin, A.D. Gladun, V.G. Leiman, V.L. Semenenko, and V.I. Ryzhii. Parametric instability in a nanoelectromechanical detector of modulated terahertz radiation on the basis of a high electron mobility transistor with a mobile elastic gate. Journal of Communications Technology and Electronics, 54(11):1322 E330, 2009.
	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.
[v-ryzhii-11:2009]	A.Satou, V. Ryzhii, V. Mitin, and N. Vagidov. Damping of plasma waves in two-dimensional electron systems due to contacts. Physica Status Solidi (B), 246(9):2146 E149, 2009.
	We report on the numerical study of plasma waves in two-dimensional electron systems with contacts using the kinetic electron transport model. We simulate the time- and position-dependence of plasma waves in the system by initially adding small perturbation of the electron concentration from the steady state. We demonstrate that in such a system the damping of plasma waves caused by out of phase electrons exiting the channel through the contacts occur. We find that the damping rate is proportional to the electron average velocity and inversely proportional to the channel length.
[v-ryzhii-12:2009]	O.G. Balev, F.T. Vasko, and V. Ryzhii. Carrier heating in intrinsic graphene by a strong dc electric field. Physical Review B, 79(16):165432(8), 2009.
	We consider the heating of carriers in an intrinsic graphene in a strong dc electric field. The intraband energy relaxation due to acoustic phonon scattering and the interband generation-recombination transitions due to thermal radiation are taken into account. The distributions of nonequilibrium carriers are obtained for the cases when the carrier-carrier scattering is unessential and when the intercarrier Coulomb scattering effectively establishes the quasiequilibrium distribution with the temperature and the density of carriers determined by the balance equations. Due to an interplay between weak energy relaxation and generation-recombination processes, the nonlinear response is characterized by a very low threshold electric field. The nonlinear current-voltage characteristics as well as the field-dependent carrier concentration are calculated for the case of the momentum relaxation associated with the elastic scattering. The obtained current-voltage characteristics exhibit a low threshold of nonlinearity and an appearance of the second ohmic region, for strong fields.

Refereed Proceeding Papers

[khmyrova-01:2009]	I.Khmyrova. Terahertz resonant frequencies of grating-bicoupled plasma wave devices. In The Int. IEEE Conf. on Microwaves, Communications, Antennas and Electronic Systems - IEEE COMCAS 2009, Tel Aviv, Israel, Nov. 2009. IEEEI.
	Resonant frequencies of plasma oscillations in the grating-bicoupled HEMT-like structures with interdigitated gates are evaluated in the presence of non-saturated source-drain current for different combinations of gate bias voltages.
[khmyrova-02:2009]	I.Khmyrova and E. Shestakova. Multi-cantilever HEMT-based resonant sensor. In The Int. IEEE Conf. on Microwaves, Communications, Antennas and Electronic Systems - IEEE COMCAS 2009, Tel Aviv, Israel, Nov. 2009. IEEEI.
	The paper deals with the analysis of resonant sensor based on micro-machined high-electron mobility transistor (HEMT) in which multiple suspended resonant cantilevers serve as floating gates. An equivalent circuit of the resonant sensor has been developed and used to simulate its frequency response using IsSpice software.
[khmyrova-03:2009]	I.Khmyrova. ‘Fringing field impact on resonant frequency in THz plasma wave devices. In Progress In Electromagnetics Research Symposium PIERS2009, Moscow, Russia, Aug. 2009.
	To analyze the impact of fringing electric field on the performance of THz plasma wave devices the concept of gate extention is used. he distributions of electric field and sheet el ectron density at the 2DEG surface are calculated. The dependemce of the resonant plasma frequency on the fringing field is obtained.
[m-ryzhii-09:2009, v-ryzhii-13:2009]	V.Ryzhii, M. Ryzhii, M.S. Shur, and V. Mitin. Negative terahertz dynamic conductivity in electrically induced lateral p-i-n junction in graphene. In 18th Int. Conf. Electronic Properties of Two- Dimensional Systems (EP2DS), Kobe, Japan, July 2009.
	We propose a device based on a gated graphene structure with electrically induced lateral p-i-n juction - graphene tunneling transit-time diode (GT-diode) and study its high-frequency characteristics.
[m-ryzhii-10:2009]	E. Ryzhii, M. Ryzhii, and D. Wei. Computer simulation study of gender differences in cardiac repolarization: normal case and the Brugada syndrome. In Ext. Abst. of 13th Int. Congress of the Int. Society for Holter and Noninvasive Electrocardiology (ISHNE 2009), Yokohama, Japan, June 2009.
	Gender differences in electrocardiographic (ECG) manifestations affect on the arrhythmia susceptibility, notably in Brugada syndrome frequently diagnosed in males (8:1 ratio male:female), but the underlying mechanisms are still unknown. We included gender differences in the ten Tusscher human ventricular cell model adjusting densities of the L-type Ca current (ICal), transient outward K (Ito), and rapid delayed rectifier K current (IKr) according to experimental data. Thesimulated action potentials for male and female cases were inputted into a state-ofthe- art 3D whole-heart model and corresponding ECG waveforms were calculated. The obtained results demonstrate that in female case cardiac cells have longer action potential duration and the surface ECG is characterized by longer QT interval. Male cardiac cells have prominent phase-1 repolarization, and are more susceptible to all-or-none repolarization, which facilitate the appearance of the Brugada syndrome manifestations on the surface ECG. These results are supported by previous clinical findings.
[m-ryzhii-11:2009, v-ryzhii-14:2009]	V.Ryzhii, M. Ryzhii, M.S. Shur, and V. Mitin. Graphene tunneling transit-time device with electrically induced p-i-n junction. In 34th Int. Conf. on Infrared, Millimeter, and Terahertz Waves (IRMM-THz 2009), Pusan, Korea, Sept. 2009.
	We propose a graphene tunneling transit-time device based on a heterostructure with a lateral p-i-n junction electrically induced in the graphene layer, develop the device model, and calculate its ac characteristics. Using the developed device model, it is shown that the ballistic transit of electrons and holes generated due to interband tunneling in the i-section results in the negative ac conductance in the terahertz frequency range. The device can serve as an active element of terahertz oscillators.
[m-ryzhii-12:2009, v-ryzhii-15:2009]	M. Ryzhii, V. Ryzhii, T. Otsuji, and V. Mitin. Graphene nanoribbon and graphene bilayer photodetectors: models and characteristics. In 14th Int. Conf. on Narrow Gap Semiconductors and Systems, Sendai, Japan, July 2009.
	Using the proposed device models for GNR-PD and GBL-PD, we calculate the dark current, responsivity, and dark current limited detectivity. The similarity and distinctions of the characteristics of GNR-PDs and GBL-PDs are discussed.
[m-ryzhii-13:2009, v-ryzhii-16:2009]	V. Ryzhii, A. Satou, A.A. Dubinov, M. Ryzhii, N. Ryabova, V.Ya. Aleshkin, and T. Otsuji. Possibility of terahertz lasing in optically excited multiple-graphene layer structures. In Int. Symp. on Quantum Nanophotonics and Nanoelectronics (ISQNN 2009), Tokyo, Japan, Nov. 2009.
	Using the developed device model, it is shown that the utilization of multiple graphene layer structures can provide relatively low threshold optical excitation level of THz lasing associated with the negative dynamic conductivity in the THz range of frequencies.
[m-ryzhii-14:2009, v-ryzhii-17:2009]	V. Ryzhii, M. Ryzhii, V. Mitin, and M.S. Shur. Negative dynamic conductivity in graphene tunneling transit-time device. In 14th Int. Conf. on Narrow Gap Semiconductors and Systems, Sendai, Japan, July 2009.
	In this communication, we analyze the proposed graphene tunneling transit-time (G-TUNNETT) device. This device is based on a graphene layer with the source and drain contacts and two gates. The bias voltages of different polarity applied to the gates result in the formation of a lateral p-i-n junction. The depleted isection serves as the interband tunneling injector of electron-hole pairs as well as the transit region. As demonstrated using the developed device model, owing to a strong sensitivity of the tunneling rate to the electric field and relatively short electron and hole transit times across the i-section, the real part of the GTUNNETT source-drain dynamic conductivity can be negative in the terahertz range of frequencies.
[m-ryzhii-15:2009, v-ryzhii-18:2009]	V. Ryzhii, M. Ryzhii, A. Satou, El M. Amine, and T. Otsuji. Emission of terahertz radiation due to self-excitation of plasma oscillations in optically pumped graphene. In Int. Conf. on Solid-State Devices and Materials (SSDM 2009), Sendai, Japan, Oct. 2009.
	The spectra of plasma oscillations in single- and periodic structures with optically pumped graphene are calculated and the self-excitation of plasma oscillations in such structures is considered in connection with the concept of terahertz emitter utilizing these oscillations.
[m-ryzhii-16:2009, v-ryzhii-19:2009]	A. Dubinov, V. Aleshkin, M. Ryzhii, T. Otsuji, and V. Ryzhii. Terahertz laser on optically pumped graphene: Concept and its substantiation. In Int. Conf. on Solid-State Devices and Materials (SSDM 2009), Sendai, Japan, Oct. 2009.
	We consider and substantiate the concept of terahertz (THz) lasers with the resonant cavity of the Fabri-Perot type utilizing the optically pumped epitaxial doublegraphene layer (double-GL) structure and multiple-graphene-layer (multiple-GL) structure with a highly conducting botton GL as the active media.
[m-ryzhii-17:2009]	E. Ryzhii, M. Ryzhii, and D. Wei. Extension of whole-heart model by coupling with human ventricular cell model. In Progress In Electromagnetics Research Symposium (PIERS 2009), Moscow, Russia, Aug. 2009. The Electromagnetics Academy.
	The experimental possibilities for studying cardiac arrhythmias in human ventricular myocardium are very limited. Thus, the utilization of computer simulation is an important alternative method. In this work, we extend 3D whole-heart model by coupling with ion channel human ventricular cell model developed by ten Tusscher et al. We adopted the model of the action potential of human ventricular cells to simulate sex differences in accordance to experimental data for male and female hearts of different species. Using the extended model the surface 12-lead Electro-cardiogram (ECG) waveforms were simulated. The obtained results conform adequately to the available clinical reports. The developed extended model can reproduce a variety of electrophysiological behaviors and provides a good basis for understanding the genesis of ECG under normal and abnormal conditions.
[m-ryzhii-18:2009, v-ryzhii-20:2009]	V. Ryzhii, M. Ryzhii, A. Satou, and T. Otsuji. Selfexcitation of terahertz plasma oscillations in optically pumped graphenebased heterostructures. In 8th Topical Workshop on Heterostructure Microelectronics (TWHM 2009), Nagano, Japan, Aug. 2009. IEICE.
	In this paper, we discuss a concept of THz emitter utilizing the self-excitation of the plasma oscillations in graphene-based heterostructures with optical pumping and determine the conditions of the plasma oscillations self-excitation (plasma instability).
[m-ryzhii-19:2009, v-ryzhii-21:2009]	V. Ryzhii, M. Ryzhii, M.S. Shur, and V. Mitin. Graphene tunneling transit-time diode for terahertz generation: proposal, model, and analysis. In Int. Meeting for Future of Electron Devices Kansai (IMFEDK 2009), Osaka, Japan, May 2009.
	Using developed model, we calculated the graphene tunneling transit-time diode (G-TUNNETT) ac conductance (admittance) as a function of the signal frequency and applied bias voltages. It is demonstrated that the ballistic transit of electrons and holes generated owing to interband tunneling leads to the negative ac conductivity in the terahertz frequency range.
[v-ryzhii-22:2009]	H. Karasawa, T. Komori, T. Watanabe, M. Suemitsu, V. Ryzhii, and T. Otsuji. Observation of carrier relaxation and recombination dynamics in optically pumped epitaxial graphene heterostructures using terahertz emission spectroscopy. In Photonics Europe 2009, Brussels, Belgium, May 2009.
	Using the terahertz emission spectroscopy, the relaxation and recombination dynamics in optically pumped epitaxial graphene heterostructures have been studied experimentally. The characteristic times of energy relaxation of the photogenerated electrons and holes and their life were estimated.
[v-ryzhii-23:2009]	V. Ryzhii. Graphene-based infrared and terahertz devices: concepts and characteristics. In 2009 Advanced Research Workshop Future Trends in Microelectronics: Unmapped Roads, page (invited), Sardinia, Italy, June 2009.
	In this paper, the features of the physical processes responsible for the device operation (specifics of the energy spectra of electrons and holes, photogeneration and tunneling injection, energy relaxation and recombination, plasma properties), the device characteristics (threshold of lasing, spectral dependences, detector responsivity and detectivity, and voltage tuning) limiting performance, and the feasibility of their realization are considered and discussed.
[v-ryzhii-24:2009]	V.Ya. Aleshkin, A.A. Dubinov, and V. Ryzhii. Graphene terahertz laser. In 17th Int. Symp. ’Nanostructures: Physics and Modeling E Minsk, Belarus, June 2009.
	We consider a terahertz laser based on optically pumped graphene layer and bilayer as the active media and suggested waveguide structure. Using the developed model, we calculate the spectral dependences the dynamic conductivity of the optically pumped graphene layer and bilayer associated with the interband and intraband transitions, estimate the pumping optical power required for lasing, and demonstrate the feasibility of realization of such a laser.
[v-ryzhii-25:2009]	T. Otsuji, Y. Tsuda, H. Karasawa, T. Suemitsu, M. Suemitsu, E. Sano, and V. Ryzhii. Emission of terahertz radiation from two-dimensional electron systems in semiconductor nano-heterostructures. In 17th Int. Symp. ’Nanostructures: Physics and Modeling E page (invited), Minsk, Belarus, June 2009.
	This paper reviews recent advances in emission of terahertz radiation from twodimensional (2D) electron systems in semiconductor nano-heterostructures. 2D plasmon resonance is first presented to demonstrate intense broadband terahertz emission from InGaP/InGaAs/GaAs material systems. The device structure is based on a high-electron mobility transistor and incorporates authors Eoriginal doubly interdigitated grating gates. Second topic focuses on graphene, a monolayer carbon-atomic honeycomb lattice crystal, having attracted attention due to its peculiar carrier transport and optical properties holding massless and gapless energy spectrum. Stimulated terahertz emission from femtosecond laser pumped epitaxial graphene is experimentally observed, reflecting the occurrence of population inversion. lateral p-i-n junction in graphene.
[v-ryzhii-26:2009]	A. Satou, F.T. Vasko, T. Otsuji, and V. Ryzhii. Population inversion and negative dynamic conductivity in optically pumped graphene. In 2009 Int. Conf. on Simulation of Semiconductor Processes and Devices, San Diego, USA, Sept. 2009.
	We study nonequilibrium carriers (electrons and holes) in an intrinsic graphene at low temperatures under infrared optical pumping. We calculate the energy distributions of carriers using a quasi-classical kinetic equation. It is found that the nonequilibrium distributions are determined by an interplay between weak energy relaxation on acoustic phonons and generation-recombination processes as well as by the effect of pumping saturation. We show that at certain pumping power density the population inversion as well as the dynamic negative conductivity can take place in terahertz and far-infrared frequencies, suggesting the possibility of utilization of graphene under optical pumping for optoelectronic applications, in particular, lasing at such frequencies.

Unrefereed Papers

[khmyrova-04:2009]	I.Khmyrova and M. Fukuda. Plasma resonances in multi-gate terahertz devices with 2DEG. In The 2010 IEICE General Conf., Sendai, Japan, Mar. 2010.
	Resonant plasma frequencies are evaluated in interdigitated grating-gated HEMTlike structures.
[khmyrova-05:2009]	I.Khmyrova. Impact of cap layer on plasma frequencies in HEMTbased terahertz devices. In The 2009 IEICE Society Conf., Niigata, Japan, Sept. 2009.
	The model based on equivalent circuit approach is proposed and used for IsSpice simulation to study the possible impact of the cap layer on frequency performance of HEMT-based terahertz devices.
[m-ryzhii-20:2009]	E. Ryzhii, M. Ryzhii, and D. Wei. A study of M-cells allocation using an algorithm of action potential duration distribution with 3D whole heart model. In IEICE Conference on Medical Engineering and Bio Cybernetics (MBE), Tamagawa, Japan, March 2010. IEICE.
	The distribution of M-cell regions within ventricular wall is not well determined. Experimental data suggest that M-cells are located in the layers with variable depth in the myocardium. The purpose of this study is to investigate the influence of different configurations of midmyocardial layer allocation on the action potential duration (APD) and surface ECG. For this purpose we proposed a novel algorithm for APD spatial distribution and implemented it together with the combined ion-channel and 3D whole 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.
[m-ryzhii-21:2009, v-ryzhii-27:2009]	V. Ryzhii, M. Ryzhii, T. Otsuji, and V. Mitin. Detectors of terahertz and infrared radiation based on p-i-n single- and multiple- graphene layer structures. In IEICE Conference on Functional Nano Device and Related Technology (ED), Okinawa, Japan, Feb. 2010. IEICE.
	Detectors of terahertz and infrared radiation based on p-i-n graphene structures utilizing interband transitions are proposed and evaluated. Using the developed device model, the detector responsivity and detectivity is calculated as functions of the number of graphene layers, energy of photons, bias voltage, and temperature. It is demonstrated that the proposed detectors can substantially surpass in the terahertz and middle infrared spectral ranges quantum-well and quantum-dot detectors as well as detectors based on narrow-gap and gapless bulk semiconductors

Grants

[v-ryzhii-28:2009]br>	V. Ryzhii. Grant-in-Aid (S) from the Japan Society for Promotion of Science (JSPS): Terahertz plasma wave nanoelectronic devices, 2006-2011.
[v-ryzhii-29:2009]	V. Ryzhii. Grant from the Japan Science and Technology Agency, CREST: Development of Graphene on Silicon (GOS) device modeling technology, 2007-2012.

Academic Activities

[khmyrova-06:2009]	Irina Khmyrova, 2008. Senior Member, IEEE
[khmyrova-07:2009]	Irina Khmyrova, 2008. Member, American Physical Society, USA
[m-ryzhii-22:2009]	M. Ryzhii.Dec. 2002-. Senior Member, IEEE
[m-ryzhii-23:2009]	M. Ryzhii.July 1995-. Member (lifelong), American Physical Society
[m-ryzhii-24:2009]	M. Ryzhii. Reviewer for The Journal of Physics D: Applied Physics
[m-ryzhii-25:2009]	M. Ryzhii. Reviewer for Semiconductor Science and Technology Journal
[m-ryzhii-26:2009]	M. Ryzhii. Reviewer for Solid State Electronics Journal
[m-ryzhii-27:2009]	M. Ryzhii. Reviewer for Journal of Physics: Condensed Matter
[m-ryzhii-28:2009]	M. Ryzhii. Reviewer for Semiconductor Science and Technology Journal
[v-ryzhii-30:2009]	V. Ryzhii. Fellow (1994-present), IEEE
[v-ryzhii-31:2009]	V. Ryzhii. Fellow (1995, lifelong), American Physical Society
[v-ryzhii-32:2009]	V. Ryzhii. Reviewer for Physical Review B Journal
[v-ryzhii-33:2009]	V. Ryzhii. Reviewer for Physical Review B Journal
[v-ryzhii-34:2009]	V. Ryzhii. Reviewer for Physical Review Letters Journal
[v-ryzhii-35:2009]	V. Ryzhii. Reviewer for Applied Physics Letters Journal
[v-ryzhii-36:2009]	V. Ryzhii. Reviewer for Journal of Physics Condensed Matter
[v-ryzhii-37:2009]	V. Ryzhii. Reviewer for Semiconductor Science and Technology Journal
[v-ryzhii-38:2009]	V. Ryzhii. Reviewer for Journal of Applied Physics
[v-ryzhii-39:2009]	V. Ryzhii. Reviewer for Nanotechnology Journal
[v-ryzhii-40:2009]	V. Ryzhii. Reviewer for Solid-State Electronics Journal
[v-ryzhii-41:2009]	V. Ryzhii,2009 E010. Member of the Editorial Board of Journal of Applied Physics
[v-ryzhii-42:2009]	V. Ryzhii,2009 E010. Member of the Editorial Board of Applied Physics Letters
[v-ryzhii-43:2009]	V. Ryzhii, 2006 E010. Member of the Int. Advisory Committee and the Editorial Board of Optoelectronics Review Int. Journal

Ph.D., Master and Graduation Theses

[khmyrova-08:2009]	Makoto Fukuda. Graduation Thesis: Tunable plasma resonances in multi-gate HEMT-like structures, University of Aizu, 2009.
	Thesis Advisor: I. Khmyrova
[khmyrova-09:2009]	Keita Takeshita. Graduation Thesis: Analysis of the impact of cap layer on plasma resonant frequencies in terahertz HEMT-based devices, University of Aizu, 2009.
	Thesis Advisor: I. Khmyrova
[m-ryzhii-29:2009]	Takumi Serizawa. Graduation Thesis: Mobile learning for natural science education: motion of bodies on a light pulley, University of Aizu, 2010.
	Thesis Advisor: M. Ryzhii
[m-ryzhii-30:2009]	Naoki Takamatsu. Graduation Thesis: Mobile learning of natural science with DoJa: Interactions of point charges, University of Aizu, 2010.
	Thesis Advisor: M. Ryzhii

2011 THE UNIVERSITY OF AIZU ALL RIGHTS RESERVED