Computer Solid State Physics Laboratory

Victor I. Ryzhii 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. 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 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). Quantum-well and quantum-dot infrared photodetectors (QWIPs and QDIPs), QWIP- and QWIP-based functional devices. Theory and computer modeling of zero-resistance and zero-conductance states in two-dimensional 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., J. Phys, Phys. Stat Sol., IEICE Trans., and others) and presented at different international conferences. The computer Solid State Physics Laboratory conducts research in cooperation with leading research groups at: Rensselaer Polytechnic Institute (Troy, USA) Tohoku University (Sendai, Japan), University at Buffalo (Buffalo, USA), Ioffe Physical-Technical Institute (St. Petersburg, Russia), Gothenburg University (Gothenburg, Sweden), and others.

Refereed Journal Papers

[khmyrova-01:2005]	A.Satou, I.Khmyrova, A.Chaplik, V.Ryzhii, and M.S.Shur. Spectrum of plasma oscillations in a slot diode with a two-dimensional electron channel. Jpn. J. Appl. Phys., 44:2592-2595, 2005.
[m-ryzhii-01:2005]	V. Ryzhii, M. Ryzhii, I. Khmyrova, T. Otsuji, and Shur M.S. Resonant terahertz photomixing in integrated high-electron-mobility transistor and quantum-well infrared photodetector device. Jpn. J. Appl. Phys., 45(4B):3648-3651, 2006.
	We propose a novel heterostructure device for generating of terahertz (THz) radiation based on the integration of a high-electron-mobility transistor (HEMT) and a quantum-well infrared photodetector (QWIP) and utilizing the photomixing of middle- or far-infrared optical signals. The operation of the photomixer under consideration is associated with the resonant excitation of plasma oscillations in the device HEMT section brought about by the transient photocurrent produced in the QWIP by incident infrared radiation. Using the developed device model for HEMT-QWIP photomixers which combines both the analytical description of electron processes and their ensemble Monte Carlo particle modeling, we evaluate the device performance.
[m-ryzhii-02:2005]	V. Ryzhii, A. Satou, I. Khmyrova, M. Ryzhii, T. Otsuji, V. Mitin, and M. S. Shur. Plasma effects in lateral Schottky junction tunneling transit-time terahertz oscillator. J. Phys. - Conf. Ser., 38:228-233, 2006.
	We study the plasma oscillations in a two-dimensional electron channel with a reverse-biased Schottky junction. Using the developed model we show that the negative dynamic conductivity of the Schottky junction associated with the tunneling injection and electron-transit-time effect can result in the selfexcitation of plasma oscillations (plasma instability) in the quasineutral portion of the channel serving as a resonant cavity. The spectrum of plasma oscillations and the conditions of their self-excitations are expressed via the structure parameters. The instability can be used in a novel diode device - lateral Schottky junction tunneling transit-time terahertz oscillator.
[v-ryzhii-01:2005]	V.I. Ryzhii. Microwave-induced negative conductivity and zeroresistance states in two-dimensional electron systems: history and current status. Physics - Uspekhi, 48(2):191-198, 2005.
	The history of the effect of absolute negative conductivity in semiconductor structures and its current studies are briefly reviewed. We focus primarily on this effect in two-dimensional electron systems in magnetic field under microwave radiation in the context of the so-called zero-resistance as well as zero-conductance states observed in recent experiments.
[v-ryzhii-02:2005]	A. Satou, I. Khmyrova, A. Chaplik, V. Ryzhii, and Shur M.S. Spectrum of plasma oscillations in a slot diode with a two-dimensional electron channel. Jpn. J. Appl. Phys., 44(4B):2592-2595, 2005.
	We strictly calculate the spectrum of plasma oscillations in a slot diode containing a two-dimensional electron channel with strip-like highly conducting contacts. The spectrum of plasma oscillations in a gated two-dimensional electron channel (without contacts) is calculated as well. We use the hydrodynamic electron transport model involving a two-dimensional Poisson equation. It is shown that the features of the structure geometry affect the oscillation spectrum.
[v-ryzhii-03:2005]	M. Hanabe, T. Otsuji, T. Ishibashi, T. Uno, and Ryzhii V. Modulation effects of photocarriers on the terahertz plasma-wave resonance in high-electron mobility transistors under interband photoexcitation. Jpn. J. Appl. Phys., 44(6A):3842-3847, 2005.
	Two-dimensional (2-D) electron plasma in a submicron channel of a highelectron mobility transistor (HEMT) is excited by interband photoexcitation, resulting in performing the photomixing function. The injected photoelectrons modulate the total 2-D electron density, affecting the plasma resonant properties. The modulation depth of the density of 2-D electrons by the photoelectrons deeply relates to the resonant intensity and fr. This effect was modeled analytically in the 2-D plasma hydrodynamic equation. In order to validate the analytical calculation, the plasma-wave resonance was experimentally observed for a 0.15-um gate-length InGaP/InGaAs/GaAs pseudomorphic HEMT in the terahertz range. At the modulation depth of 30with a double peak (the peak at 1.9/5.8 THz corresponding to the fundamental/third harmonic resonance). The resonant frequencies slightly shifted downward and the intensity attenuated with decreasing the modulation depth. Observed resonant frequencies support the analytical calculation.
[v-ryzhii-04:2005]	Ryzhii V. Microwave-induced suppression of dissipative conductivity and its Shubnikov-de Haas oscillations in two-dimensional electron systems: effects of dynamic electron localization and plasma reflection. Jpn. J. Appl. Phys., 44(9A):6600-6606, 2005.
	We present a model for microwave photoconductivity in two-dimensional electron systems (2DESs) in a magnetic field at microwave frequencies lower than the electron cyclotron frequency when the intra-Landau level (LL) transitions dominate. Using this model, we explain the effect of the decrease in the 2DES dissipative conductivity (and resistivity) and smearing of its Shubnikov-de Haas oscillations caused by microwave radiation observed recently. The model invokes the concept of suppression of elastic impurity scattering of electrons by the microwave electric field. We calculated the dependence of the 2DES conductivity associated with intra-LL transitions as a function of the radiation and cyclotron frequencies and microwave power. We take into account the effect of plasma reflection of microwaves from 2DES resulting in a distinction between the ac microwave electric field acting on electrons and that generated by a microwave source. The obtained dependences are consistent with the results of recent experimental observations.
[v-ryzhii-05:2005]	A. Satou, V. Ryzhii, and Chaplik A. Plasma oscillations in twodimensional electron channel with non-ideally conducting side contacts. J. Appl. Phys., 98(1 August):034502-034506, 2005.
	We calculate the spectrum and damping rate of plasma oscillations in a twodimensional electron channel with striplike side contacts, taking into account the finite value of the conductivity of side contacts. We use a hydrodynamic electron-transport model for electrons both in the two-dimensional electron channel and contacts, with the Poisson equation for the self-consistent electric potential. It is shown that in the real channels the damping rate can markedly increase due to the influence of nonideally conducting side contacts.
[v-ryzhii-06:2005]	V. Ryzhii, A. Satou, W. Knap, and M. S. Shur. Plasma oscillations in high-electron-mobility transistors with recessed gate. J. Appl. Phys., accepted, 2006.
	We calculate the plasma oscillation spectrum in high-electron-mobility transistors (HEMTs) with recessed gate having the highly doped caps adjacent to the source and drain contacts and the windows between the caps and the gate. The resonant plasma frequencies are found as functions of the lengths of the gate, cap, and window regions, the electron concentration in the transistor channel, and the gate voltage. We demonstrate that the effect of cap region can result in a significant reduction of the resonant frequencies in comparison with those calculated for simplified HEMT model. This can provide a plausible explanation of the data obtained in recent experimental studies of the detection of terahertz radiation in and its emission from HEMTs.
[v-ryzhii-07:2005]	V. Ryzhii, A. Satou, I. Khmyrova, M. Ryzhii, T. Otsuji, V. Mitin, and M. S. Shur. Plasma effects in lateral Schottky junction tunneling transit-time terahertz oscillator. J. Phys. - Conf. Ser., 38:228-233, 2006.
	We study the plasma oscillations in a two-dimensional electron channel with a reverse-biased Schottky junction. Using the developed model we show that the negative dynamic conductivity of the Schottky junction associated with the tunneling injection and electron-transit-time effect can result in the selfexcitation of plasma oscillations (plasma instability) in the quasineutral portion of the channel serving as a resonant cavity. The spectrum of plasma oscillations and the conditions of their self-excitations are expressed via the structure parameters. The instability can be used in a novel diode device - lateral Schottky junction tunneling transit-time terahertz oscillator.
[v-ryzhii-08:2005]	V. Ryzhii and A. Satou. Plasma effects in transistors and their terahertz applications. IEICE Technical Report, 105(629):29-37, 2006.
	We review concepts associated with applications of plasma waves and oscillations in two-dimensional electron gas in heterostructures for different compact and effective terahertz devices.
[v-ryzhii-09:2005]	V. Ryzhii, A. Satou, and M. S. Shur. Plasma instability and terahertz generation in HEMTs due to electron transit-time effect. IEICE Trans. Electron., accepted, 2006.
	We study the coupled spatio-temporal variations of the electron density and the electric field (electron plasma oscillations) in high-electron mobility transistors using the developed device model. The excitation of electron plasma oscillations in the terahertz range of frequencies might lead to the emission of terahertz radiation. In the framework of the model developed, we calculate the resonant plasma frequencies and find the conditions for the plasma oscillations self-excitation (plasma instability). We show that the transit-time effect in the high-electric field region near the drain edge of the channel of high-electron mobility transistors can cause the self-excitation of the plasma oscillations. It is shown that the self-excitation of plasma oscillations is possible when the ratio of the electron velocity in the high field region, and the gate length, i.e., the inverse transit time are sufficiently large in comparison with the electron collision frequency in the gated channel. The transit-time mechanism of plasma instability under consideration can superimpose on the Dyakonov-Shur mechanism predicted previously strongly affecting the conditions of the instability and, hence, terahertz emission. The instability mechanism under consideration might shed light on the origin of terahertz emission from high electron mobility transistors observed in recent experiments.
[v-ryzhii-10:2005]	V. Ryzhii, M. Ryzhii, I. Khmyrova, T. Otsuji, and Shur M.S. Resonant terahertz photomixing in integrated high-electron-mobility transistor and quantum-well infrared photodetector device. Jpn. J. Appl. Phys., 45(4B):3648-3651, 2006.
	We propose a novel heterostructure device for generating of terahertz (THz) radiation based on the integration of a high-electron-mobility transistor (HEMT) and a quantum-well infrared photodetector (QWIP) and utilizing the photomixing of middle- or far-infrared optical signals. The operation of the photomixer under consideration is associated with the resonant excitation of plasma oscillations in the device HEMT section brought about by the transient photocurrent produced in the QWIP by incident infrared radiation. Using the developed device model for HEMT-QWIP photomixers which combines both the analytical description of electron processes and their ensemble Monte Carlo particle modeling, we evaluate the device performance.

Refereed Proceeding Papers

[khmyrova-02:2005]	I.Khmyrova, M.Ryzhii, M.S.Shur, and V. Ryzhii. Resonant terahertz heterostructure photomixer with lateral Schottky junction. In Digest of the 13th Conference on Microwave Techniques (COMITE 2005), Prague, Czech Republic, Sep. 2005.
[khmyrova-03:2005]	V.Ryzhii, I.Khmyrova, M.Ryzhii, S.-Y.Lin, and J.Y.Chi. Integration of quantum well and quantum dot infrared photodetectors with a field-effect transistor. In Microtechnogies for a New Millenium, Sevilla, Spain, May. 2005.
[m-ryzhii-03:2005]	V. Ryzhii, A. Satou, I. Khmyrova, M. Ryzhii, T. Otsuji, V. Mitin, and M.S. Shur. Plasma effects in lateral Schottky junction tunneling transit time terahertz oscillator. In 7th Int. Conf. on New phenomena in Mesoscopic Systems / 5th Int. Conf. on Surfaces and Interfaces of Mesoscopic Devices (NPMS-7/SIMD-5), Maui, Hawaii, pages 60-61, Nov. - Dec. 2005.
[m-ryzhii-04:2005]	V. Ryzhii, I. Khmyrova, M. Ryzhii, S.-Y. Lin, and J.Y Chi. Integration of quantum well and wuantum dot infrared photodetectors with a field-effect transistor. In Microtechnogies for a New Millenium, Sevilla, Spain, May 2005.
[m-ryzhii-05:2005]	I. Khmyrova, M. Ryzhii, M.S. Shur, and V. Ryzhii. Resonant terahertz heterostructure photomixer with lateral Schottky junction. In The 13th Conference on Microwave Techniques (COMITE 2005), Prague, Czech Republic, Sep. 2005.
	We study a heterostructure device with the structure akin to a high-electron mobility transistor which can be used to generate electro-magnetic radiation in the terahertz range of frequencies. The gated electron channel is supplied with a lateral Schottky contact serving as the source.
[m-ryzhii-06:2005]	V. Ryzhii, V. Ryzhii, I. Khmyrova, T. Otsuji, and M.S. Shur. Resonant Terahertz Photomixing in Integrated HEMT-QWIP Device. In 2005 Int. Conference on Solid State Devices and Materials, Kobe, Japan, Sep. 2005.
	Novel terahertz photomixing device based on integration of a HEMT and QWIP has been proposed. The proposed device has been assessed theoretically using the developed analytical and numerical models. We have shown that the HEMT-QWIP resonant photomixer can effectively transform infrared signals (radiation of two infrared lasers with close frequencies or ultrashort infrared pulses) into terahertz signals.
[m-ryzhii-07:2005]	M. Ryzhii, I. Khmyrova, V. Ryzhii, T. Otsuji, and M.S. Shur. Modeling of plasma oscillations and terahertz photomixing in HEMTlike heterostructure with lateral Schottky junction. In SPIE Int. Symposium 'Microelectronics, MEMS, and Nanotechnology', Brisbane, Australia. SPIE, SPIE, Dec. 2005.
	We study theoretically a heterostructure device with the structure akin to a high-electron mobility transistor which can be used to generate electromagnetic radiation in the terahertz range of frequencies. The gated electron channel is supplied with a lateral Schottky contact serving as the source. The operation of the device is associated with photomixing of optical signals in high-electric-field depletion region of the Schottky junction. The electrons and holes photogenerated in the Schottky junction depletion region and propagating across it induce the ac current in the quasi-neutral electron channel which, in turn, excites the plasma oscillations in this channel. Fast electron transport in the Schottky junction depletion region and resonant properties of the electron channel provide an enhanced response of the photomixer to optical signals at the plasma frequencies.
[m-ryzhii-08:2005]	V. Ryzhii, A. Satou, I. Khmyrova, M. Ryzhii, and T. Otsuji. Terahertz photomixing in UTC-photodiode with electron resonant cavity. In 9th Int. Symposium on Contemporary Photonics Technology (CPT2006), Tokyo, Japan, Jan. 2006.
	We propose the integration of a uni-traveling-carrier (UTC) photodiode with an electron resonant (ER) cavity for generation of terahertz radiation using photomixing of optical signals and assess the device performance invoking analytical and numerical models.
[m-ryzhii-09:2005]	M. Ryzhii, V. Ryzhii, and M.S. Shur. Resonant terahertz photomixing devices based on integration of QWIP and HEMT utilizing plasma effects. In Int. Workshop on Quantum Well Infrared Photodetectors (QWIP2006), Kandy, Sri-Lanka, accepted 2006.
	In this paper, we propose novel devices with the structure comprising a QWIP integrated with a HEMT, develop their models, calculate the device characteristics, and discuss the device ultimate performance.
[v-ryzhii-11:2005]	T. Otsuji, M. Hanabe, T. Nishimura, N. Imamura, E. Sano, and V. Ryzhii. Widely-tunable terahertz plasmon-resonant photomixer based on heterostructure integrated microelectronics. In The 35th Workshop: Physics and Technology of THz Photonics, Erice, Italy, July 2005.
	Specific features of two-dimensional plasmons in a submicron high-electron moblity transistor (HEMT) promote resonant oscillations in the terahertz range. We've proposed a novel plasmon-resonant terahertz photomixer as a frequency-tunable CW source that can improve the conversion gain and radiation power.
[v-ryzhii-12:2005]	V. Ryzhii, A. Satou, and M.S. Shur. Plasma instability and terahertz generation in HEMTs due to electron transit-time effect. In The 6th Topical Workshop on Heterostructure Microelectronics (TWHM2005), Awajii Island, Japan, pages 60-61, August 2005.
	In this paper, we discuss different mechanisms of plasma instability in HEMTs which can be responsible for terahertz emission observed experimentally, focusing our consideration on the electron transit-time mechanism.
[v-ryzhii-13:2005]	V. Ryzhii, A. Satou, I. Khmyrova, M. Ryzhii, T. Otsuji, V. Mitin, and M.S. Shur. Plasma effects in lateral Schottky junction tunneling transit time terahertz oscillator. In 7th Int. Conf. on New phenomena in Mesoscopic Systems / 5th Int. Conf. on Surfaces and Interfaces of Mesoscopic Devices (NPMS-7/SIMD-5), Maui, Hawaii, pages 60-61, Nov. - Dec. 2005.
[v-ryzhii-14:2005]	V. Ryzhii, I. Khmyrova, M. Ryzhii, S.-Y. Lin, and J.Y Chi. Integration of quantum well and wuantum dot infrared photodetectors with a field-effect transistor. In Microtechnogies for a New Millenium, Sevilla, Spain, May 2005.
[v-ryzhii-15:2005]	V. Ryzhii, A. Satou, I. Khmyrova, M. Ryzhii, and T. Otsuji. Terahertz photomixing in UTC-photodiode with electron resonant cavity. In 9th Int. Symposium on Contemporary Photonics Technology (CPT2006), Tokyo, Japan, Jan. 2006.
	We propose the integration of a uni-traveling-carrier (UTC) photodiode with an electron resonant (ER) cavity for generation of terahertz radiation using photomixing of optical signals and assess the device performance invoking analytical and numerical models.

Grants

[m-ryzhii-10:2005]

M Ryzhii. Subsidy of Fukushima Prefectural Foundation for Advancement of Science and Education, 2005-2006.

Academic Activities

[khmyrova-04:2005]	Irina Khmyrova, 2004. Senior Member, The Institute of Electrical and Electronics Engineers, USA (1994.03 - to present)
[khmyrova-05:2005]	Irina Khmyrova, 2004. Member, American Physical Society, USA (1995.07 - lifelong membership)
[m-ryzhii-11:2005]	M Ryzhii, Dec. 2002. Senior Member, IEEE (1996.01 - present)
[m-ryzhii-12:2005]	M Ryzhii, July 1995. Member (lifelong), American Physical Society (1995.07 - present)
[v-ryzhii-16:2005]	V Ryzhii, March 2004. Corresponding Member (1987.12-present), Russian Academy of Sciences (Branch of Informatics, Computer Engineering and Automation)
[v-ryzhii-17:2005]	V Ryzhii, March 2004. Fellow Member (1994.03-present), IEEE
[v-ryzhii-18:2005]	V Ryzhii, March 2004. Fellow Member (1995.07-present), American Physical Society

Ph.D and Other Theses

[khmyrova-06:2005]	A. Yamada. Graduation Thesis: Simulation of HEMT performance using equivalent-circuit model, University of Aizu, 2005. Thesis Advisor: I. Khmyrova
[khmyrova-07:2005]	Yu. Seijyo. Graduation Thesis: Development of distributed circuit model for HEMT-like structure, University of Aizu, 2005. Thesis Advisor: I. Khmyrova

2007 THE UNIVERSITY OF AIZU ALL RIGHTS RESERVED