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EN
The conditions for THz radiation generation caused by electron transite time resonance in momentum and real spaces under low-temperature optical-phonon emission are analyzed. It is shown that such a phenomenon provides a unique possibility to realize the sub-THz and THz radiation generation at the border of the electrooptical and electronic techniques by using both the approaches: (i) amplification of transverse electromagnetic waves in 3D bulk materials and 2D quantum wells, and (ii) longitudinal current instabilities in submicron and overmicron n⁺nn⁺ diodes.
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Modeling of THz-Electro-Optical Sampling Measurements

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EN
We carry out a theoretical analysis of THz-electro-optical sampling experimental technique applied to semiconductor structures. The difficulties/impossibility of determining the small-signal conductivity spectrum in the framework of such a technique are analyzed and discussed.
EN
The problems related with the intrinsic noise in FET/HEMT channels induced by continuous branching of the total current between channel and gate are considered in the framework of a simple analytical model and its predictions on the current-noise spectra. Main branching-induced effects such as the appearance of an additional noise related to the excitation of plasma waves, its dependence on FET/HEMT embedding circuits, interference properties, etc. are analysed.
FR
Monte Carlo simulations of high-field transport in semiconductor nitrides, GaN and InN, is used to calculate the velocity-field characteristics and the high-frequency behavior of the differential mobility, spectral density of velocity fluctuations, and noise temperature. It is found that due to very short relaxation time scales of nitrides, the characteristic frequencies associated with extrema and cutoff decay of the negative differential mobility, etc. are shifted to higher frequency range with respect to the case of standard A_3B_5 compounds. This property is favorable for applications of nitrides in the THz frequency range.
EN
We report Monte Carlo simulations of electronic noise in heavily doped nanometric GaAs Schottky-barrier diodes operating in series with a parallel resonant circuit when a high-frequency large-signal voltage is applied to the whole system. Significant modifications of the noise spectrum with respect to the unloaded diode are found to occur in the THz-region.
EN
Experimental results of direct measurement of resonant terahertz emission optically excited in InGaAs HEMT channels are presented. The emission was attributed to two-dimensional plasma waves excited by photogeneration of electron-hole pairs in the HEMT channel at the frequency of the beating of two cw-laser sources. The presence of resonances for the radiation emission in the range of f_0 ± 10 GHz (with f_0 from 0.3 up to 0.5 THz) detected by a Si-bolometer is found. The intensity of THz emission exhibits a nonlinear growth with increase of the pumping power.
EN
Calculations of the small-signal response of InGaAs HEMTs by using the hydrodynamic approach coupled with a pseudo-2D Poisson equation are performed. The spectra of small-signal admittance and impedance are found to demonstrate series of the resonant peaks corresponding to excitation of plasma waves. Possibilities and conditions of instability onset and THz signal detection are discussed.
EN
By means of a numerical hydrodynamic model, we consider the mechanism of collective plasma oscillations in a field-effect transistor channel under different excitations and biasing conditions. First, we consider the case of a device externally-excited by a harmonic optical beating or an electronic excitation under constant current condition at the drain. Both situations exhibit sharp resonances related to the first odd plasma modes illustrating the possibility of using the HEMT as a terahertz photomixer or detector. Then, we demonstrate that the frequencies, amplitudes and quality factors of the resonances can be strongly modified by varying the drain biasing condition from current- to voltage-driven operation.
EN
We report measurements of the pulsed and dc current-voltage characteristics of AlGaN/GaN high-electron-mobility transistors as functions of geometry, temperature (from 300 down to 15 K), and operating conditions. An increase in the drain current with shortening of the pulse width from 1 μs to 400 ns is found to be significant at room temperature whilst this behavior is inverted or even removed at 77 and 15 K temperatures.
EN
We report transmission measurements of GaN quantum well grown on sapphire substrate in the 220-325 GHz frequency band at low temperatures. A significant enhancement of the transmitted beam intensity with the applied voltage on the devices under test is found.
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