


 Department of Computer Hardware 
 Computer Solid State Physics Laboratory 

    
 Victor I. Ryzhii Professor  Vladimir V'yurkov Visiting Professor  Irina I. Khmyrova Assistant Professor  Maxim V. Ryzhii Assistant Professor 


The research activity of the Computer Solid State Physics Laboratory is focused on theoretical studies and computer modeling of physical processes in semiconductor micro and nanostructures and in novel electronic and optoelectronic classical and quantum devices based on such structures. A substantial part of activity of the laboratory is associated with the development of Internet interactive educational resources and materials. Since the laboratory establishment in 1993, its members have published more than 120 journal articles and made more than 120 presentations at international conferences. Among the members of the laboratory there are one Corresponding Member of the Russian (National) Academy of Sciences and three IEEE Senior Members. The research efforts of the laboratory members are now centered on theory and computer modeling of:
 Semiconductor classical and quantum heterostructure devices operating in the terahertz range of frequencies (terahertz detectors mixers, generators, and photomixers).
 Quantumwellandquantumdotinfraredphotodetectors((QWIPsandQDIPs), QWIP and QWIPbased functional devices.
 Electronic and optoelectronic devices based on semiconductor heterostructures with lateral pn junctions.
 Theory and computer modeling of zeroresistance and zeroconductance states in twodimensional electron systems irradiated with microwaves and related phenomena.


Original research results obtained in this academic year have been published in refereed journal papers (published in J. Appl. Phys., Jpn. J. Appl. Phys., Physica E, Physical Review, IEEETrans. On Electron Devices, and others) and presented at different international conferences. The computer Solid State Physics Laboratory conducts research in cooperation with leading research groups at:
 Kyushu Institute of Technology (Kyoto, Japan),
 Wayne State University (Detroit, USA),
 Sensor Electronic Technology, Inc. (Columbia, USA),
 Ioffe Physical
 Technical Institute (St. Petersburg, Russia),
 Chalmers Institute of Technology (Gothenburg, Sweden), and others.



 [khmyrova01:2003]  S. Oktyabrsky, I. Khmyrova, and V.Ryzhii. Characteristics of integrated QWIPHBTLED upconverter. IEEE Trans. on Electron Devices, 50:23782387, 2003.
We evaluate characteristics of anovel device based on integration of a quantumwell infrared photodetector(QWIP),a heterostructure bipolar transistor (HBT),anda lightemitting diode(LED) for upconversion of middle infrared (IR) into near IR (visible) radiation 
 [khmyrova02:2003]  A. Satou, V. V'yurjov, and I.Khmyrova. Plasma oscillations in terahertz photomixing highelectronmobility transistor structure on p+substrate. Jpn.J.Appl.Phys., 43:L566L568, 2004.
The effect of heavily doped p+substrateonplasma oscillations in the channel of a highelectronmobility transistor is considered. 
 [mryzhii01:2003]  M. Ryzhii, V. Ryzhii, and V. Mitin. Electricfield and spacecharge distributions in InAs/GaAs quantumdot infrared photodetectors: ensemble Monte Carlo particle modeling. Microelectronics J., 34(5):411414, 2003.
We proposed a simplified quasithreedimensional model for nonequilibrium electron transport in quantum dot infrared photodetectors (QDIPs) based on an ensemble Monte Carlo particle method. Invoking the developed model, we calculated the electricfield and spacecharge distributions, in InAs/GaAs and InGaAs/GaAs QDIPs. 
 [mryzhii02:2003]  V. Ryzhii, I. Khmyrova, M. Ryzhii, and V. Mitin. Comparison of dark current, responsivity and detectivity of different intersubband infrared photodetectors. Semicond. Sci. Technol., 19(1):816, 2004.
This paper deals with the comparison of quantum well, quantum wire and quantum dot infrared photodetectors (QWIPs, QRIPs and QDIPs, respectively) based on physical analysis of the factors determining their operation. The operation of the devices under consideration is associated with the intersubband (intraband) electron transitions from the bound states in QWs, QRs and QDs into the continuum states owing to the absorption of infrared radiation. The redistribution of the electric potential across the device active region caused by the photoionization of QWs, QRs and QDs affects the electron injection from the emitting contact. The injection current provides the effect of current gain. Since the electron thermo emission and capture substantially determine the electric potential distribution and, therefore, the injection current, these processes are also crucial for the device performance. To compare the dark current, responsivity and detectivity of QWIPs,QRIPs and QDIPs we use simplified but rather general semiphenomenological formulae which relate these device characteristics to the rates of the thermoemission and photoemission of electrons from and their capture to the QWs and the QRandQD arrays. These rates are expressed via the photoemission crosssection, capture probability and so on, and the structural parameters. Calculating the ratios of the QWIP, QRIP and QDIP characteristics using our semiphenomenological model, we show that: the responsivity of QRIPs and QDIPs can be much higher than the responsivity of QWIPs, however, higher responsivity is inevitably accompanied by higher dark current; the detectivity of QRIPs and QDIPs with lowdensity arrays of relatively large QRs and QDs is lower than that of QWIPs; the detectivity of QRIPs and QDIPs based on dense arrays can significantly exceed the detectivity of QWIPs. 
 [mryzhii03:2003]  M. Ryzhii, V. Ryzhii, and M. Shur. Effect of nearballistic photoelectron transport on resonant plasmaassisted photomixing in highelectron mobility transistors. Semicond. Sci. Technol., 19(0):in press, 2004.
We analyse photomixing using a structure akin to a highelectron mobility transistor. We develop a device model which takes into account the resonant excitation of plasma oscillations in the highelectron mobility transistor and nearballistic transport of the photogenerated carriers. The transport of the photogenerated carriers is considered using an ensemble Monte Carlo particle modelling. It is shown that the velocity overshoot due to nearballistic propagation of just photogenerated electrons can substantially increase the eAEciency of the resonant photomixing and generation of terahertz radiation. 
 [vryzhii01:2003]  V. Ryzhii, A. Satou, and M. Shur. Admittance of a slot diode with a twodimensional electron channel. J. Appl. Phys., 93(12):1004110045, 2003.
We calculate the frequencydependent admittance of a diode with a twodimensional electron channel in a slot between striplike contacts. Hydrodynamic electron transport equations coupled with a twodimensional Poisson equation for the selfconsistent electric potential are used. Using the calculated expression for the admittance, we analyze the effect of the planar contacts and external capacitance on the plasma oscillations in the system under consideration. The obtained results are useful for the interpretation of experimental observation of plasma effects in highelectron mobility transistors and optimization of terahertz devices based on these transistors. 
 [vryzhii02:2003]  V. Ryzhii and A. Satou. Electricfield breakdown of absolute negative conductivity and supersonic streams in twodimensional electron systems with zero resistance/conductance states. J. Phys. Soc. Japan, 72(11):27182721, 2003.
We calculate the currentvoltage characteristics of a twodimensional electron system (2DES) subjected to a magnetic field at strong electric fields. The interaction of electrons with piezoelectric acoustic phonons is considered to be a major scattering mechanism governing the currentvoltage characteristics. It is shown that at a suAEciently strong electric field corresponding to the Hall drift velocity exceeding the velocity of sound, the dissipative current exhibits an overshoot. The overshoot of the dissipative current can result in a breakdown of the absolute negative conductivity caused by microwave irradiation and, therefore, can substantially affect the formation of the domain structures with the socalled zeroresistance and zeroconductance states and supersonic electron streams. 
 [vryzhii03:2003]  V. Ryzhii and V. Vyurkov. Absolute negative conductivity in twodimensional electron systems associated with acoustic scattering stimulated by microwave radiation. Phys. Rev. B, 68(16):165406 165414, 2003.
We discuss the feasibility of absolute negative conductivity (ANC) in twodimensional electron systems (2DES's) stimulated by microwave radiation in a transverse magnetic field. The mechanism of ANC under consideration is associated with electron scattering on acoustic phonons accompanied by absorption of microwave photons. It is demonstrated that the dissipative components of the 2DES dc conductivity can be negative due to negative values of the dc photoconductivity caused by microwave radiation at certain ratios of the microwave frequency and the electron cyclotron frequency. The phase of the oscillations of the dissipative dc photoconductivity associated with photonassisted electron scattering on acoustic phonons is quite different from that in the case of the photonassisted impurity scattering mechanism. The concept of ANC associated with an interplay of the scattering mechanismscanbe invokedto explainthe natureof the occurrence of zeroresistance 'dissipationless' states observed in recent experiments. 
 [vryzhii04:2003]  V. Ryzhii. Microwave photoconductivity in twodimensional electron systems due to photonassisted interaction of electrons with leaky interface phonons. Phys. Rev. B, 68(19):193402193406, 2003.
We calculate the contribution of the photonassisted interaction of electrons with leaky interface phonons to the dissipative dc photoconductivity of a twodimensional electron system in a magnetic field. The calculated photoconductivity as a function of the frequency of microwave radiation and the magnetic field exhibits pronounced oscillations. The obtained oscillation structure is different from that in the case of photonassisted interaction with impurities. We demonstrate that at a suAEciently strong microwave radiation in certain ranges of its frequency (or in certain ranges of the magnetic field) this mechanism can result in absolute negative conductivity. 
 [vryzhii05:2003]  V. Ryzhii and R. Suris. Nonlinear effects in microwave photoconductivity of twodimensional electron systems. J. Phys. Cond. Matt., 15(40):68556869, 2003.
We present a model for microwave photoconductivity of twodimensional electron systems in a magnetic field which describes the effects of strong microwave and steadystate electric fields. Using this model, we derive an analytical formula for the photoconductivity associated with photon and multiphotonassisted impurity scattering as a function of the frequency and power of microwave radiation. According to the developed model, the microwave conductivity is an oscillatory function of the frequency of microwave radiation and the cyclotron frequency which becomes zero at the cyclotron resonance and its harmonics. It exhibits maxima and minima (with absolute negative conductivity) at microwave frequencies somewhat different from the resonant frequencies. The calculated power dependence of the amplitude of the microwave photoconductivity oscillations exhibits pronounced sublinear behaviour similar to a logarithmic function. The height of the microwave photoconductivity maxima and the depth of its minima are nonmonotonic functions of the electric field. The possibility of a strong widening of the maxima and minima due to a strong sensitivity of their parameters on the electric field and the presence of strong longrange electricfield fluctuations is pointed to. The obtained dependences are consistent with the results of the experimental observations. 
 [vryzhii06:2003]  V. Ryzhii, V. Vyurkov, P.O. Vaccaro, and T. Aida. Physics and characteristics of lateral pn junction tunneling transistor. Physica E,21(2):867871, 2004.
The explicit model of a lateral pn junction tunneling transistor is developed and the currentvoltage characteristics are obtained. 
 [vryzhii07:2003]  L. Pichl, L.M. Schmidt, V. Ryzhii, M. Kimura, and J. Horacek. Tunneling effects in concentric disk quantum dots: discretediscrete and discretecontinuum limits. Phys. Stat. Solidi (c), 238(3):815401543, 2003.

 [vryzhii08:2003]  G.P. Nikishkov, I. Khmyrova, and V. Ryzhii. Finite element analysis of selfpositioning microstructures and nanostructures. Nanotechnology, 14(7):820823, 2003.
The finite element method is used formodelling of selfpositioning microstructures and nanostructures. The geometrically nonlinear problem with large rotations and large displacements is solved using a step procedure with coordinate updating after each step. It is shown that the real shape of the selfpositioning structures is rather complicated and the analytical formulae have limited applicability in the estimation of such parameters as the curvature radius and/or angle of elevation. 
 [vryzhii09:2003]  A. Satou, I. Khmyrova, V. Ryzhii, and M.S. Shur. Plasma and transittime mechanisms of the terahertz radiation detection in highelectronmobility transistors. Semicond. Sci. Technol., 18(6):460469, 2003.
We develop a device model for a highelectronmobility transistor (HEMT) affected by the incoming terahertz radiation. The model takes into account the electron plasma oscillations in the HEMT channel, tunnelling of electrons from the channel into the gate layer and electron transittime effects in this layer. It is shown that the excitation of plasma oscillations accompanied by the delay in the electron propagation across the gate layer and a strong nonlinearity of the tunnelling current can result in significant features of the HEMT highfrequency linear and nonlinear characteristics. We derive a formula for the HEMT gatetosource/drain admittance. We also calculate the variation of the dc current induced by the terahertz radiation and the HEMT detection responsivity. It is found that the detection responsivity exhibits sharp resonant peaks corresponding to the frequencies of plasma oscillations. The resonant plasma frequencies and the positions of the admittance and detection responsivity peaks depend on the gate length and the lengths of the contact regions (sourcetogate and gatetodrain spacings) and can be tuned by the gate voltage. The coincidence of the plasma and transittime resonances can lead to a marked sharpening of the responsivity peaks. 

 Refereed Proceeding Papers 

 [khmyrova03:2003]  V.Ryzhii, I. Khmyrova, and M.Shur. Terahertz photomixing using plasma oscillations in a twodimensional heterostructure focal plane arrays. In SPIE's First Int. Symposium on Microtechnologies for the New Millenium, pages 340345, Gran Canaria, Canary Islands, Spain,, May 2003.
We address the problem of photomixing using twodimensional heterostructures akin to a highelectron mobility transistor. It is shown that the velocity overshoot of just photogenerated electrons can substantially increase the eAEciency of the resonant photomixing and generation of terahertz radiation. 
 [mryzhii04:2003]  V. Ryzhii, M. Ryzhii, andM. Shur. Combined ensemble Monte Carlo particle and hydrodynamic model for terahertz photomixing devices. In Editor K.Seabelfeld, editor, IVth IMACS Seminar on Monte Carlo methods, pages 2123, Berlin, Sept. 2003. IMACS, WIAS.
Optical methods of generation of electromagnetic radiation in the terahertz (THz) rangeare fairly effectiveand simple. Recently, a conception of THzphotomixing using the excitation of plasma oscillations in heterostructures akin to highelectron mobility transistors (HEMTs) has been proposed. To assess the performance of HEMTbased photomixers and find approaches for their optimization a computer simulation is indispensable. The features of the system in question are associated with nonequilibrium transport of the electrons and holes photogenerated in the device absorption region and the electron plasma oscillation in the twodimensional channel. Non equilibrium character of the transport of the photogenerated electrons and holes propagating mainly perpendicular to the channel plane necessitates the use of an ensemble Monte Carlo particle technique. In contrast, the electron system in the channel has rather large concentration. The frequency of the electronelectron collisions in the channel is significantly higher that the frequency of the electron collisions with phonons and impurities. This makes the electron system in the channel an ideal object for hydrodynamic modeling. In ourpaper we discuss the model for the HEMTlike photomixer utilizing the excitation of plasma oscillations by nonequilibrium photoelectrons and photoholes which is based on a combination of Monte Carlo and hydrodynamic approaches and show some results of our simulations. 
 [mryzhii05:2003]  V. Ryzhii, M. Ryzhii, and M. Shur. Modeling of the excitation of terahertz plasma oscillations in aHEMTby ultrashot optical pulses. In Editor Y.Nakano, editor, 3rd. Int. Conf. on Numerical Simulation of Semiconductor Optoelectronic Devices (NUSOD'03), pages 8485, NewYork, Oct. 2003. IEEE/LEOS, IEEE.
We report devicemodels forHEMTbasedTHz source: an allanalytical model and a model in which the electron system in the channel is considered analytically in linear approximation, whereis the transport of the photogenerated electrons and holes is treated invoking an ensemble Monte Carlo particle simulation 
 [mryzhii06:2003]  A. Satou, I. Khmyrova, M. Ryzhii, V. Ryzhii, and M. Shur. Resonant terahertz photomixers based on highelectron mobility transistors. In EditorK.Tada, editor, 7th Int. Symp. on Contemporary Photonics Technology (CPT2004), pages 2122, Tokyo, Jun. 2004. CRL, CRL.
We calculate and analyze the characteristics of recently proposed terahertz photomixers based on highelectron mobility transistors utilizing the resonant excitation of the plasma oscillations in the device electron channel by the photogenerated electrons and holes 
 [vryzhii10:2003]  V. Ryzhii, I. Khmyrova, and M. Shur. Terahertz photomixing using plasma oscillations in a twodimensional heterostructure. In Editor R. Vajtai, editor, Proceedings of SPIE Vol.15, Nanotechnology, pages 340345, Bellingham, May 2003. SPIE, SPIE  The International Society for Optical Engineering.
We address the problem of photomixing using twodimensional heterostructures akin to a highelectron mobility transistor. 
 [vryzhii11:2003]  V. V'yurkov, A. Vetrov, and V. Ryzhii. Pseudogap and spin polarization in a twodimensional electron gas. InChairZh. Alferov, editor, 11th Symp. 'Nanostructures: Physics and Technology, pages 351352, St Petersburg, June 2003. Ioffe PhysicoTechnical Institute, Ioffe PhysicoTechnical Institute.
Tunnel density of states in the vicinity of Fermi level of a twodimensional electron gas (2DEG) subject to an external magnetic filed is calculated.It reveals a pseudogap recently observed in the experiments. 
 [vryzhii12:2003]  V. Ryzhii, V. Vyurkov, P.O. Vaccaro, and T. Aizda. Physics and characteristics of lateral pn junction tunneling transistor. In Chair Y.Arakawa, editor, 11th Int. Conf. onModulated Semiconductor Structures (MSS11), pages482483, Tokyo, July2003. Institute of Industrial Science, University of Tokyo, Institute of Industrial Science, University of Tokyo.
The explicit model of a lateral pn junction tunneling transistor is developed and the currentvoltage characteristics are obtained. 
 [vryzhii13:2003]  V. Vyurkov, A. Satou, V. Ryzhii, and M. Shur. The effect of p+substrate on terahertz oscillations in a nhighelectron mobility transistor. In Editors K. Hirakawa, H. Ito, editor, 11th Int. Conf. on Terahertz Electronics (THz 2003), page 123, Sendai, Japan, Sep. 2003. RIKEN, RIKEN.

 [vryzhii14:2003]  V. Ryzhii, A. Satou, M. Ryzhii, I. Khmyrova, and M. Shur. Characteristics of a terahertz source based on a HEMT with optical input through the ungated regions. In Editors K. Hirakawa, H. Ito, editor, 11th Int. Conf. on Terahertz Electronics (THz 2003), page 78, Sendai, Japan, Sep. 2003. RIKEN, RIKEN.

 [vryzhii15:2003]  V. Ryzhii, A. Satou, I. Khmyrova, M. Ryzhii, V. Vyurkov, and M. Shur. Device model for HEMTbased resonant terahertz photomixers. In Editor N.Hiramoto, editor, 28th Int. Conf. on Infrared amd Millimeter Waves (IRMMW 2003), pages PDP56, Otsu, Japan, Oct. 2003. JSAP, CRL, JSIR, JSAP.
We develop a device model for recently proposed terahertz photomixers (TPMs) based on highelectronmobility transistors (HEMTs). The TPM operation is associated with the excitation of plasma oscillations in the HEMT channel. This results in the resonant response of TPMs to optical signals. We evaluate the effect of the TPM structural parameters on its performance. 
 [vryzhii16:2003]  V. Ryzhii. Absolute negative conductivity in twodimensional electron systems under microwave radiation. In Chair T. Ogino, editor, Int Symp. on Functional Semiconductor Nanosystems (FSNS 2003), page 52, Atsugi, Japan, Nov. 2003. NEDO, JST, NTT Basic Research Lab., JSAP, JSAP.

 [vryzhii17:2003]  V. Ryzhii. Mechanism of absolute negative conductivity and 'dissipationless' states in twodimensional electron systems stimulated by microwaves. In Chairs D.K. Ferry, C. Hamaguchi, editor, New Phenomena in Mesoscopic Structures 6 and Surfaces and Interfaces in Mesoscopic Devices 4, pages 8889, Maui, Hawaii, Dec. 2003. ONR, JSPS, JSPS.

 [vryzhii18:2003]  M. Shur and V. Ryzhii. Plasma wave electronics devices. In Proc. of 2003 Int. Semiconductor Device Research Symp. (, pages WP70710, Washington DC, Dec. 2003. IEEEEDS, ARL, ARO, NSF.

 



 [mryzhii07:2003]  M Ryzhii. Subsidy of Fukushima Prefectural Foundation for Advancement of Science and Education, 20032004. 


 [khmyrova04:2003]  Irina Khmyrova, 2003.
Senior Member, The Institute of Electrical and Electronics Engineers, USA(1994.03  to present) 
 [khmyrova05:2003]  Irina Khmyrova, 2003.
Member, American Physical Society, USA (1995.07  lifelong membership) 
 [khmyrova06:2003]  Irina Khmyrova, 2003.
Associate Member, The Third World Organization for Women in Science, Trieste, Italy (1992.02  to present) 
 [mryzhii08:2003]  M Ryzhii, March 2003.
Senior Member, IEEE (1996.01  present) 
 [mryzhii09:2003]  M Ryzhii, March 2003.
Member (lifelong), American Physical Society (1995.07  present) 
 [vryzhii19:2003]  V. Ryzhii, Apr. 2003.
Corresponding Member, Russian Academy of Sciences (Branch of Informatica, Computer Engineering and Automation)(1987.12  present) 
 [vryzhii20:2003]  V. Ryzhii, Apr. 2003.
Fellow Member, IEEE (1994.03  present) 
 [vryzhii21:2003]  V. Ryzhii, Apr. 2003.
Member (lifelong), American Physical Society (1995.07  present) 
 [vryzhii22:2003]  V. Ryzhii, Apr. 2003.
Member, Japan Society of Applied Physics (1993.11  present) 
 [vryzhii23:2003]  V. Ryzhii, Apr. 2003.
Member, IEICE Japan (1993.07  present) 
 [vryzhii24:2003]  V. Ryzhii, Apr. 2003.
Member of Editorial Board, Journal 'Microelectronics' (Russian Academy of Sciences)(1990.01  present) 
