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We perform the numerical simulation of the characteristics of normally-off GaN/AlGaN HEMT transistors with a p-gate. The dependences of the threshold voltage on the thickness of the main AlGaN barrier and additional spacer and stop AlN layers are determined. The effect of the incomplete compensation of the spontaneous charge during passivation on the output characteristics of the transistor is analyzed. The effect of the ohmic resistance of the source on the saturation current of the transistor is studied. It is shown that the saturation current with the optimal design parameters can reach 1 A/mm at a gate voltage of Vg ~ 3 V.

The GaN based devices with respect to most parameters exceed the devices based on traditional semiconductor materials. The AlGaN-transistors are the devices, operating in the depletion mode. For most applications it is necessary to implement the operating mode E, when the current in the channel is closed at zero gate voltage. In this paper the novel method namely using the p-GaN layer under the gate has been considered. The plasma-chemical removal of p-GaN layer in the non-gated active region has been chosen as a formation method of this layer. In this case the challenges, namely the non-uniformity in the depth of etching and poor control of the etching rate, arise. To exclude these problems, the heterostructures with additional AlN barrier layer has been developed. The research results of the heterostructure parameters affecting the carrier concentration in the channel, and, respectively, the transistor output characteristics have been presented and the developed design process has been shown. According to it the normally-off transistors have been formed. The maximum drain current in the open state is 350 mA/mm at 4 V gate voltage and the breakdown voltage is about 550 V in closed state at 0 V gate voltage.

The effect of atomic composition on the rate of the plasma-chemical etching of silicon nitride in high-power transistors based on an AlGaN/GaN heterojunction is studied. It is shown how the subsequent process of its plasma-chemical etching depends on the configuration of the incorporation of hydrogen impurity atoms into the molecular structure of silicon nitride deposited in the plasma. The dependence of the etching rate on the process parameters (the working pressure in the chamber, the plasma-generator power, the working-gas flows, and the deposition temperature) is investigated. It is shown that the etching rate of the HxSirNzHy film is independent directly on the hydrogen content but significantly depends on the ratio of [Si–H]/[N–H] bonds. The etching rate of HxSirNzHy in high-density plasma at low powers is much less dependent on the configuration of hydrogen bonds than the etching rate of this dielectric in a buffer etchant.

For silicon carbide, the problem of obtaining low-resistance ohmic contacts with improved service characteristics remains topical despite a significant body of experimental data. The influence exerted by the composition of Ni and TiAl metallization, alloying parameters, additional doping of the contact layer of silicon carbide (SiC) with N+ nitrogen ions, and the crystallographic Si- or C-face on the resistance of ohmic contacts to n-6H-SiC is examined. It is found that the greatest influence on how ohmic contacts to n-6H-SiC are formed is exerted by the alloying process resulting in a decrease in the contact resistance by approximately six times. The process of additional doping with N+ also reduces the contact resistance by nearly a factor of four. It is found that low-resistance contacts can be obtained on both faces with approximately the same low resistance. TiAl metallization is optimal for the C-face, and Ni metallization, for the Si-face. This choice of metallization makes it possible to obtain ohmic contacts on both polar faces with approximately the same resistances on the order of 2.5 × 10–4 Ω cm2.

4H-SiC was irradiated with Al+ions at an energy of 190 keV. The depth profiles of implanted aluminum were obtained using the secondary ion mass spectrometry method; a comparison was made with profiles calculated in the SRIM program. Using Rutherford backscattering in channeling mode, we studied the amorphization of the crystal structure after ion implantation in the target at room temperature and 400° C. The fluence of 1015 cm−2 was shown to completely disorder the crystal structure under irradiation of a room temperature target. It was found that after ion irradiation of a target heated to 400° C, the penetration depth of the embedded impurity increases. An increase in the target temperature during irradiation leads to the recombination of a significant number of simple defects and the restoration of the crystal structure. The topography of the samples before and after ion irradiation was compared.

It is shown that intentionally undoped high-resistance GaN buffer layers in AlGaN/GaN heterostructures with high electron mobility for transistors can be formed by ammonia molecular beam epitaxy. The GaN growth conditions have been optimized using calculations of the background impurity and point defect concentrations at different ratios of the gallium and ammonia fluxes.

The state-of-the-art long-distance near-infrared optical radars use laser-diode-based miniature pulsed transmitters producing optical pulses of 3–10 ns in duration and peak power typically below 40 W. The duration of the transmitted optical pulses becomes a bottleneck in the task of improving the radar ranging precision, particularly due to the progress made in developing single photon avalanche detectors. The speed of miniature high-current drivers is limited by the speed of the semiconductor switch, either a gallium nitride field-effect transistor, the most popular alternative nowadays, or a silicon avalanche bipolar junction transistor (ABJT), which was traditional in the past. Recent progress in the physical understanding of peculiar 3-D transients promises further enhancement in speed and efficiency of properly modified ABJTs, but that is not the only factor limiting the transmitter speed. We show here that a low-inductance miniature transmitter assembly containing only a specially developed capacitor, a more advanced transistor chip than that used in commercial ABJTs and a laser diode, has allowed peak power from 40 to 180 W to be reached in optical pulses of 1–2 ns in duration without after-pulsing relaxation oscillations. This finding is of interest for compact low-cost, long-distance decimeter-precision lidars, particularly for automotive applications.

In this paper, we investigated the influence of doping a GaN buffer with iron Fe and carbon C on the static characteristics of DC normally open HEMT AlGaN/AlN /GaN transistors, as well as on their high-frequency RF characteristics. The simulation showed that the high-frequency characteristics of the transistor in which the buffer layer is not doped with iron or carbon changed little when the buffer is doped with iron or carbon, up to concentrations of 5 • 1017 (cm-3). A little change has occurred at extremely high concentrations 1 • 1018, 1 • 1019 (cm-3). A comparison of the simulation results for a buffer doped with iron and carbon shows that the effect of pushing the current from the depth of the buffer to the channel region is most pronounced when the buffer is doped with carbon. Thus, at a concentration of 1 • 1018 (cm-3) doping of the buffer with carbon, the depth of current penetration into the buffer decreases to a value of 0.10 mkm, with a buffer thickness of 2.00 mkm.

The preparation of ohmic contacts to heterobipolar nanostructures has a number of characteristic features. In addition to the basic requirement of minimizing contact resistance, contacts to this type of structures have a transition layer whose depth of penetration must not exceed the emitter layer’s thickness, due to the possibility of short-circuiting the emitter base p–n junction. In this work, the effect the main technological parameters of rapid thermal annealing have on a contact’s characteristics are examined, and the process of obtaining a low-resistance ohmic contact to heterobipolar transistor layers is optimized. Ohmic contacts to the n-layers of heterobipolar nanoheterostructures based on gallium arsenide and produced via layer-by-layer electron-beam deposition of Ge/Au/Ni/Au are considered. The diffusion distribution profiles of doping with Ge impurities are calculated as a function of the time and temperature of rapid thermal annealing, and are examined via scanning electron microscopy. It is found that rapid thermal annealing for 60 s at a temperature of 398°C yields ohmic contacts with low resistance, smooth surface morphology, and the minimum size of the transition layer.

The conditions for the growth of epitaxial layers are considered and the resistance of alloyed ohmic contacts to tellurium-doped gallium arsenide layers is studied. The use of the (AuGe eutectic alloy)-Ni–Au composition alloy of ohmic contacts to the gallium arsenide layers with electron conductivity, including use as a contact layer of a narrow-band (In0.5Ga0.5As), makes it possible to achieve a resistance of 10–7 Ohm cm2, in the best case; however, this leads to a deterioration of the surface morphology. In this paper, we study the issues of doping the GaAs contact layer by tellurium to the maximum concentration of 2.5 × 1019 cm–3. In this case, the resistance of the ohmic contacts proves to be less than 5 × 10–8 Оhm cm2, simultaneously with the improvement of the semiconductor’s surface morphology.

GaN technology has been waiting to be widely adopted because of its specific technical requirements. Integration of transistor and driver in a single die will enable to overcome problems with gate driving, high cost of circuit and low device reliability. This paper demonstrates technology of GaN-on-Si normally-on and normally-off transistor with different p-GaN cap-layer thickness as well as simulation of these devices. The simulation data confirm experimental results. P-GaN cap-layer thickness affects the current channel density: the more p-GaN thickness, the less channel density. The fabricated transistors have a maximum drain current in open state of about 800 mA/mm.

This paper investigates ohmic contacts to n-GaAs layers of the heterobipolar nanoheterostructures obtained through electron-beam evaporation of Ge, Au, Ni, and Au layer-by-layer. The effect of the firing time and temperature on the contact resistance is considered. Based on the analysis of the characteristics of the ohmic contacts, a firing installation of a special design and a firing technique are developed. The technique ensures the minimum contact resistance for the minimum size of a transition layer, satisfactory morphology, and even edges of the contacts.

The structure of AlN/GaN heterostructures with an ultrathin AlN barrier is calculated for normally-off transistors. The molecular-beam epitaxy technology of in situ passivated SiN/AlN/GaN heterostructures with a two-dimensional electron gas is developed. Normally-off transistors with a maximum current density of ~1 A/mm, a saturation voltage of 1 V, a transconductance of 350 mS/mm, and a breakdown voltage of more than 60 V are demonstrated. Gate lag and drain lag effects are almost lacking in these transistors.

The results devoted to the development of a method for creating an RF transistor, in which a T-shaped gate is formed by nanoimprint lithography, are presented. The characteristics of GaAs p-HEMT transistors have been studied. The developed transistor has a gate “foot” length of the order of 250 nm and a maximum transconductance of more than 350 mS/mm. The maximum frequency of current amplification f t is 40 GHz at the drain-source voltage V DS = 1.4 V and the maximum frequency of the power gain f max is 50 GHz at V DS = 3 V.

The sensitivity of classical n +/n – GaAs and AlGaN/GaN structures with a 2D electron gas (HEMT) and field-effect transistors based on these structures to γ-neutron exposure is studied. The levels of their radiation hardness were determined. A method for experimental study of the structures on the basis of a differential analysis of their current–voltage characteristics is developed. This method makes it possible to determine the structure of the layers in which radiation-induced defects accumulate. A procedure taking into account changes in the plate area of the experimentally measured barrier-contact capacitance associated with the emergence of clusters of radiation-induced defects that form dielectric inclusions in the 2D-electron-gas layer is presented for the first time.

The effect of the layer thickness and composition in AlGaN/AlN/GaN and InAlN/AlN/GaN transistor heterostructures with a two-dimensional electron gas on their electrical and the static parameters of test transistors fabricated from such heterostructures are experimentally and theoretically studied. It is shown that the use of an InAlN barrier layer instead of AlGaN results in a more than twofold increase in the carrier concentration in the channel, which leads to a corresponding increase in the saturation current. In situ dielectric-coating deposition on the InAlN/AlN/GaN heterostructure surface during growth process allows an increase in the maximum saturation current and breakdown voltages while retaining high transconductance.

A molecular beam epitaxy technology of in situ passivated SiN/AlN/GaN heterostructures with an ultrathin AlN barrier has been developed. Based on these structures, normally off transistors with maximum current density of about 1 A/mm, saturation voltage of about 1 V, transconductance up to 350 mS/mm, and breakdown voltage above 60 V have been fabricated, in which the drain and gate current collapse phenomena are virtually absent.

Polarization-induced p-type doping of AlGaN layers with high aluminum content during plasmaassisted MBE growth has been studied. It is shown that a gradient of the AlN molar fraction in AlGaN (composition gradient) on a level of 0.005 nm–1 must be set in order to obtain a hole concentration of ~1018 cm–3 (measured by the C–V method) in Al x Ga1–x N:Mg (x = 0.52–0.32) layers with dopant concentration [Mg] = 1.3 × 1018 cm–3. p–i–n photodiodes based on AlGaN heterostructures with such layers as p-emitters showed maximum photoresponsitivity in the solar-blind wavelength range (λ = 281 nm) about 35 and 48 mA/W at reverse bias voltage U = 0 and–5 V, respectively, and exhibited a dark current density of 3.9 × 10–8 A/cm2 at U =–5 V.

The phenomenon of terahertz radiation detection by resonant tunneling structures (RTSs) has been studied. The calculations of the changes ΔI0 in the direct current (DC) component I0 under the action of an alternating electric field were carried out by the solution of a nonstationary Schrodinger equation with a time-periodic electric field based on the Floquet mode expansion of the wave functions. The dependences of the DC component I0 in resonant tunneling structures on the frequency ν and AC signal amplitude Vac have been built. It is shown that the ΔI0 value in triple-barrier RTSs at resonance frequency hv ≈ Er2–Er1 (Er1 and Er2 are the energies of the size-quantized levels) can exceed a low-frequency value by more than an order of magnitude. The parameters of the structures have been optmized, in order to use them in the terahertz radiation detectors in the anbsence of an external bias. The possibility of tuning the resonance frequency in the terahertz range by changing the DC bias has been shown.

The results of experimental studies of the parameters of GaN and GaAs structures before and after γ-neutron irradiation are reported. A special set of test diodes making it possible to reduce the error in the results of measuring the parameters of the structures, which is important in the design and optimization of the structure of semiconductor devices, is suggested.

Peak power is a critical factor for sub-nanosecond-pulsed transmitters utilizing laser diodes (LD) and applied to long distance LIDARs (light detection and ranging) for drones and automotive applications. Receiver speed is not anymore a limiting factor thanks to replacing linear (typically avalanche) detectors and a broad-band amplifier with a single photon avalanche detector (SPAD). Consequently the transmitters become the bottle neck in the resolution and ranging. The simplest and lowest-possible-cost transmitter consists of a switch, an LD, a storage capacitor C, and unavoidable parasitic loop inductance L. In the resulting resonant circuit, the principal problem consists of suppressing relaxation oscillations. Traditional way of oscillation damping reduce peak current and increase the pulse width. Here we show that specific transient properties of a Si avalanche switch solves the problem automatically provided the inductance is sufficiently low. This finding advances the state-of-the-art by reaching 90 W/1ns/200 kHz pulses from a miniature low-cost transmitter based on Si avalanching bipolar junction transistor (ABJT). Besides, the same self-damping effect may be realized in other switches maintaining significant residual voltage despite of fast current reduction.

The aim of the work is to create a miniature pulse optical lidar on an infrared laser diode by means of highly effective avalanche switching in bipolar silicon transistors. Confident operation of the optical switch board at a frequency of 10 kHz with a dynamic charging circuit has been achieved. The ways of increasing the radiation power, increasing the repetition rate of pulses (necessary to improve the accuracy of the lidar) are considered.

Dependence of the chemical composition of a film of plasma-chemical silicon nitride on the technological parameters of the deposition process is studied. The stages in which the process parameters are optimized in order to improve the masking properties of the film are described. A systematic study of the Fourier-transform infra-red (IR) spectra of plasma-chemical silicon-nitride films is carried out. It is found that the chemical resistance of a silicon-nitride film depends on the configuration in which hydrogen is incorporated into chemical bonds.

A method of mark deposition for electron beam lithography was developed. It solved the problem of a dry photoresist explosion. This occurs during the deposition of refractory metals thick layers. The photoresist degradation leads to bad morphology, poor adhesion and non-linear edges of the metal. We used an additional sublayer of aluminum and carried out the molybdenium deposition process with interruptions. The final marks layer composition is 10 nm of aluminium and 150 nm of molybdenum. The optimal pause between the processes is 10 minutes, deposition step of molybdenium is 15 nm. Metallization showed good adhesion and smooth surface morphology. Electron beam lithography can recognize these marks. Annealing at the temperature of 870 degrees did not produce any significant changes. The marks have a high temperature and mechanical stability. This makes it suitable for gallium nitride based technology.

Performance of a detector based on AlGaAs/InGaAs/GaAs-material system was studied. The detector was comprised of large serpentine array of high-electron mobility transistors (HEMTs) connected in series. The floating drain contact of each transistor (except the last one) served as a source for the next one. Detection of terahertz (THz) radiation was based on the excitation of electron plasma oscillations in the HEMT's channel. The peculiarities of THz response of the detector in question including an enhanced noise-equivalent power were demonstrated.

The results of the fabrication and study of a double-barrier resonant tunneling structure grown on the basis of GaN and AlN wide-gap materials on a (0001)-oriented sapphire substrate are given. It is shown that, at voltages of ∼3 V, the current-voltage characteristics of resonant tunneling diode samples exhibit a region of negative differential conductivity that disappears upon multiple cyclic measurements. It is also shown that the reversal of sign of the applied voltage restores the initial shape of the current-voltage characteristics and an increase in the temperature of the structure from room temperature to 200°C yields irreversible degradation of the device and a shift of the region of negative differential conductivity to lower voltages

We have recently shown that only a small part of a Si bipolar junction transistor (BJT) conducts the current in a short-pulsing mode (≤ 2 ns), and a complicated temporal variation takes place in the size of operating emitter-base perimeter. Namely, the switched-on region in the corner of an emitter finger first shrinks down to just a few micrometers and only then spreads to ~ 100 μm by the end of the transient. Additionally important is the demonstrated ability of a tiny filament (≤ 10 μm) to quench the switching in the entire perimeter (1.6 mm). This creates the impression that an initial triggering inhomogeneity of the smallest size will always win the switching competition. It has been shown experimentally, however, that the sharpest corners (in size) “lose out” to the ~ 100 μm corners, a fact that has not been explained so far. It is shown here using quasi-3-D modeling that an optimal curvature for the corner of an emitter finger exists that provides minimal switching delay, resulting in the shortest current pulses of the highest amplitude. This finding is especially important when designing unique subnanosecond avalanche BJTs, the 3-D transient properties of which are of major importance.

In this paper, the high electron mobility transistor (HEMT) with p-GaN gate is developed. The article demonstrates development of normally-off p-GaN gate HEMT on heterostructure with AlN stop layer for p-GaN selective etching and formation of normally-on GaN HEMT on the same wafer. It is researched that the gate length and gate-to-drain length influence on transistor operation and its breakdown voltage. The ohmic contact resistance and leakage currents depend on etching RF mode. The developed normally-off transistor with gate length of 1 um and gate-to-drain length of 9.5um has a breakdown voltage of 500 V and drain current in open state of 350 mA/mm. It is established that 2 nm SiN under the gate metal influence on device work.

The process of ion implantation into silicon carbide is studied in this paper. We conducted an analysis of acceptor distribution profiles. We determined that silicon carbide layers with an orientation (11–20) have a higher degree of crystal lattice recovery after ion implantation with aluminum ions than a crystal lattice with an orientation (0001). A significantly higher efficiency of ion doping of silicon carbide with an orientation (11–20) was shown, which may indicate a more efficient recrystallization of the fastest growing crystallographic direction. We have established a higher degree of restoration of the crystal lattice of silicon carbide implants with an orientation (11–20) after implantation. Highly doped SiC p-layers were obtained with a specific resistance of about 0.02 Ohm*cm and with high crystalline structure quality without the use of ultra-large implantation doses. The minimum value of Rs for orientation (0001) is about 10 k Ω/□, and for orientation (11-20) - 2.7 k Ω/□.

A simple miniature source generating pulse trains with a central frequency of ∼100 GHz and a duration of 50–100 ps has been demonstrated recently. The source is based on nanometer-scale collapsing field domains (CFDs) generated in the collector of an avalanching bipolar GaAs transistor. The central frequency is determined by the domain transient time across the collector, and thus, a routine increase in the oscillation frequency from 0.1 to 0.3–0.5 THz would require a reduction in the collector thickness by a factor of 3–5. This is not acceptable, however, since it would reduce the maximum blocking voltage affecting the achievable peak current across the avalanche switch. We suggest here a solution to this challenging problem by reducing the CFD travel distance while keeping the collector thickness unchanged. Here, the discovered and interpreted phenomenon of CFD collapse when entering a dense carrier plasma zone made it possible by means of bandgap engineering. A CFD emitter generating ∼200 GHz wavetrains of ∼100 ps in duration is demonstrated. This finding opens an avenue for the increase in the oscillation frequency without any reduction in the emitted power, by using a smart structure design.

The results of the comprehensive study of LT-GaAs epitaxial structures on GaAs and Si substrates by high-energy electron diffraction, reflection anisotropy spectroscopy, atomic force microscopy, X-ray diffraction, Raman scattering, and photoluminescence methods are presented. The results obtained indicate the existence of several channels of nonequilibrium carrier recombination, which depend, in particular, on the substrate type and on the complex dependence of the concentration of structural imperfections on the used technology and growth conditions of the structures.

Current-voltage (I–V) characteristics of resonant-tunneling diode In0.53Ga0.47As/AlAs/InP structures are studied at 300 and 77 K. The peak-to-valley current ratios were determined as 22:1 and 44:1 at temperatures of 300 and 77 K, respectively, which correspond to the maximum values for InGaAs/AlAs/InP heterostructures without an additional InAs layer of a quantum subwell in their configuration.

Definition the temperature dependence of electronic components parameters needs for their using in different devices. In this paper we research the temperature dependence of the parameters of test Schottky field-effect transistor based on gallium nitride (GaN) with nanostructure heterojunction. Our measuring platform is based on a two-channel measuring unit and Agilent Technologies E5273A probe-based devices WILD M3Z microscope with a heated table and a temperature controller. We describe the structure of the measured MESFET, layout and installation of measuring current-voltage characteristics of measurement methods. The temperature dependence of the electrical parameters of test Schottky field-effect transistor are presented in table and graphic modes.

We report on development of digital circuits fabrication technique based on depletion mode AlGaN/GaN high electron mobility transistors (HEMTs) with adjusted threshold voltage. Transistors fabrication technique is based on fluorine plasma treatment of AlGaN/GaN on Sapphire HEMT gate region. Plasma treatment process based on CHF 3 /O 2 gas mixture was developed. Post-treatment annealing process was applied to improve carrier mobility, which degrades after plasma treatment due to plasma etching induced damage. Physical etching of top heterostructure layer allowed us to control maximum drain-source saturation current. We have fabricated AlGaN/GaN HEMTs with threshold voltage V th = −1.36 V, drain-source saturation current Id ss =170 mA/mm and transconductance g m =20 mS/mm. The voltage level shifter (LS) which transfer input voltage levels V IH =3÷5 V and V IL =0÷0.4 V to output voltage levels V OH = −0.4÷0 V and V OL = −40 ÷ −35 V was developed and fabricated using Ni-AlGaN/GaN HEMT Schottky diodes. Maximum supply current of LS is 10 mA. In this paper we discuss adjusted threshold voltage AlGaN/GaN HEMT fabrication technique and introduce design and measurement results of HEMTs and LS.

The-state-of-the-art in long-distance near-infrared optical radars is utilization the laser-diode-based miniature pulsed transmitters producing optical pulses of 3–10 ns in duration and peak power typically below 40 W. The bandwidth of the receiving channel nowadays exceeds 300 MHz, and thus the duration of the optical pulses exceeding 3 ns is a bottleneck in the task of high practical importance, namely increase in the radar ranging precision. Nowadays the speed of the high-current drivers is limited by the speed of a semiconductor switch that is typically field-effect transistor or an avalanche switch. The last one provides faster switching, and development of new avalanche switches is very challenging and important task, but this is not the only factor limiting the transmitter speed. Here we show that not only the switch, but also parasitic inductance in the miniature assembly and type of the capacitor play very important role in solving the problem of long-distance decimeter-precision radar.

Array of field-effect transistors (FET) with asymmetric T-gates and floating electrodes fabricated on a single chip was used as terahertz (THz) detector. Nonresonant detection with strong photovoltaic response was realized due to excitation of electron plasma oscillations in the common channel of the FETs array. Voltage responsivities obtained by the array of FETs with floating electrodes surpass the photoresponse reported for the array of FETs connected in series by external wiring.

A numerical method for electron transport calculations in resonant-tunneling GaN/AlGaN heterostructures has been developed on the basis of a self-consistent solution of the Schrodinger and Poisson equations. Dependences of the system’s transmission coefficient on the external field and of the peak current on the ratio between the well and barrier widths have been studied for a double-barrier resonant-tunneling diode. For technical applications, the optimal values of the structure’s parameters have been found.

Technology for the production of an array of ordered nanoemitters based on carbon nanotubes is developed. The technological parameters of the fabrication of carbon nanotubes are chosen. It is shown that the structures produced exhibit field electron emission with an emission current of 8 μA and a threshold voltage of 80 V

Progress in terahertz spectroscopy and imaging is mostly associated with femtosecond laser-driven systems, while solid-state sources, mainly sub-millimetre integrated circuits, are still in an early development phase. As simple and cost-efficient an emitter as a Gunn oscillator could cause a breakthrough in the field, provided its frequency limitations could be overcome. Proposed here is an application of the recently discovered collapsing field domains effect that permits sub-THz oscillations in sub-micron semiconductor layers thanks to nanometer-scale powerfully ionizing domains arising due to negative differential mobility in extreme fields. This shifts the frequency limit by an order of magnitude relative to the conventional Gunn effect. Our first miniature picosecond pulsed sources cover the 100–200 GHz band and promise milliwatts up to ∼500 GHz. Thanks to the method of interferometrically enhanced time-domain imaging proposed here and the low single-shot jitter of ∼1 ps, our simple imaging system provides sufficient time-domain imaging contrast for fresh-tissue terahertz histology.Progress in terahertz spectroscopy and imaging is mostly associated with femtosecond laser-driven systems, while solid-state sources, mainly sub-millimetre integrated circuits, are still in an early development phase. As simple and cost-efficient an emitter as a Gunn oscillator could cause a breakthrough in the field, provided its frequency limitations could be overcome. Proposed here is an application of the recently discovered collapsing field domains effect that permits sub-THz oscillations in sub-micron semiconductor layers thanks to nanometer-scale powerfully ionizing domains arising due to negative differential mobility in extreme fields. This shifts the frequency limit by an order of magnitude relative to the conventional Gunn effect. Our first miniature picosecond pulsed sources cover the 100–200 GHz band and promise milliwatts up to ∼500 GHz. Thanks to the method of interferometrically enhanced time-domain imaging proposed here and the low single-shot jitter of ∼1 ps, our simple imaging system pr...

We demonstrate a Schottky ultraviolet photodiode (UV-PD) and a UV light-emitting diode (UV-LED) based on AlGaN heterostructures grown by plasma-assisted molecular beam epitaxy. The spectral responsivity of the Schottky UV-PD is 3 mA/W at 271 nm at zero bias and decreases by two orders of magnitude for the spectral range of longer wavelengths ( > 300 nm). The sub-monolayer digital alloying technique was used for growing the AlGaN quantum wells in UV-LEDs emitting a single electroluminescence peak at 273 nm.

An array of GaAs/InGaAs/AlGaAs field-effect transistors with an asymmetric T-gate in each transistor and floating electrodes was fabricated on a single chip and tested as a detector of terahertz (THz) radiation. Principle of detection was based on excitation of plasma oscillations in the common electron channel of the FETs array. Strong terahertz photovoltaic response was demonstrated without any supplementary antenna. Voltage re-sponsivities above 1000 V/W and up to 2000 V/W were obtained at zero (unbiased mode) and positive (directed from drain to source — biased mode) dc currents in the FETs array channel, respectively, surpassing the photorespponse demonstrated by the array of FETs connected in series by external wiring [5].

Acoustic charge transport is studied experimentally and theoretically. To this end, an AlGaAs/GaAs heterostructure is designed and fabricated with set geometrical and electrical parameters of the layers. Its transfer characteristic is measured, i.e., the variation of output voltage with injection current. The behavior of the curve is explained within an analytical model. The conclusions are supported by numerical simulation.

Results of complex experiments aimed at finding a relationship between the properties of initial GaAs single-crystal wafers and epitaxial films and the threshold spectrometric characteristics of ionizing radiation detectors are reported.

Development of physical principles of THz-wave amplification and oscillation is one of problems determining progress in modern solid state electronics towards high frequencies and ultrahigh performance. Novel perspectives are tied with use of resonant tunneling quantum effects, characterized by transient times less than 1 ps, comparable with fast response of superconducting devices. The information about these properties can be obtained from investigation of high-frequency oscillations or current-voltage switching phenomena in resonant-tunneling (RTD) nanostructures. In the paper the results of theoretical and experimental studies of high-frequency properties of RTD elements in subterahertz and terahertz frequency range are presented basing on developed theory of high-frequency response in RTD as well as on experimental high-frequency investigation data and current-voltage switching phenomena investigation results of effects correspondingly related to stationary current characteristics changes in single-quantum-well as well as in doublequantum- well resonant-tunneling diode nanostructures under external electromagnetic electrical field.