Search

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.

N-Acetylmuramyl-L-alanyl-D-isoglutamine α-phenylglycoside was synthesized from α-phenyl-D-glucosaminide peracetate, which was obtained by fusing β-D-glucosamine pentaacetate with phenol and zinc chloride followed by deacetylation. α-Phenyl-N-acetylglucosaminide was converted in two steps into 4,6-O-isopropylidene-N-acetyl-D-muramic acid α-phenylglycoside, which was condensed with L-Ala-D-iGln benzyl ether using the activated ester method. Sequential removal of glycopeptide protecting groups via acid hydrolysis and catalytic hydrogenolysis gave the target product.

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.

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.

Two step decomposition procedure was developed and implemented to analyze experimentally measured EL-spectra of light-emitting diode (LED) with mesh-like top electrode and two sets of InGaN/GaN quantum wells (QWs) for blue and green emissions. At a first step EL-spectra were decomposed into basic Gaussian functions (GFs) for blue, green, and violet emission lines. Then each of the basic GFs was decomposed into the secondary GFs which give reasonable ground to relate broadening of EL-spectrum to the position dependent compensation of quantum-confined Stark effect (QCSE) in the InGaN/GaN QWs. Metal strips prevent from extraction a portion of light not only with larger intensity but also with shorter wavelength comparing to those for the light extracted from the uncovered active region. Such a “cut-off” manifests itself in longer central peak wavelengths of the basic blue and green GFs obtained by EL-spectrum decomposition comparing to the emission spectra of blue and green QWs. Analysis of basic GFs allowed to evaluate quantitatively splitting of the injected charge carriers between blue and green QWs and the third source of violet emission. This can be useful in optimization-oriented modeling of the LED's performance.

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.

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.

N-Acetylmuramyl-L-alanyl-D-isoglutamine α-cyclooctyl- and α-cyclopentadecylglycosides were synthesized. The starting peracetylated α-N-glucosaminides were synthesized by reacting the cycloalkanols with peracetyl α-D-glucosaminyl chloride in the presence of Hg(II) iodide in CH3NO2 with heating or by using ZnCl2/tetrabutylammonium bromide in CH2Cl2 at room temperature. Sequential deacetylation, isopropyl protection, and alkylation by (S)-2-bromopropanoic acid gave α-cycloalkyl-4,6-O-isopropylidene-N-acetyl-D-muramic acids, condensation of which with the benzyl ester of L-Ala-D-iGln using the HOSu/DCC method and deprotection afforded the target glycopeptides.

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.

β-Cyclooctyl-, β-cyclodecyl-, and β-cyclopentadecylglycosides of N-acetylmuramyl-L-alanyl-D-isoglutamine were prepared in yields of 39, 18, and 25%, respectively, (calculated for muramic acid) via the reaction of β-cycloalkyl-4,6-O-isopropylidene-N-acetyl-D-muramic acids with the benzyl ester of L-Ala-D-iGln using the HOSu/DCC method followed by deprotection.

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.

Light-emitting diodes (LEDs) with blue-green dual-wavelength emission and top metal electrode patterned as a mesh were fabricated using InGaN/GaN material system and tested. In pulsed voltage supply mode an increase in injected current resulted in electroluminescence (EL) with equal peak intensities of blue and green emission lines and shallow trough between them. These features of the LED EL-spectrum can be attributed to the effect of the mesh-like patterning of the top electrode.Meshed electrode promotes the injection of current spatially nonuniform along the planes of the quantum well (QWs) which results not only in spatial nonuniformity of the intensity of generated light but also may contribute to position-dependent compensation of Quantum-confined Stark effect (QCSE) resulting in blue shift of EL in the QWs. The observed phenomenon can be used to control or engineer the EL spectra of dual-wavelength LEDs by electrode patterning. Display Omitted Blue-green light-emitting diodes with mesh-like electrode demonstrate broad EL-spectrum.In EL-spectrum blue and green emission peaks are equal with shallow trough between them.Observed EL-spectrum is related to spatially nonuniform current injection.Position-dependent compensation of quantum-confined Stark effect takes place.

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 parameters of the electromagnet in the electromagnetic suspension system of the city transit vehicle are evaluated. A simulation model of the magnetic suspension system which allows studying its dynamic characteristics is created in Simulink. Air gap regulator settings are obtained using the model.

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 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 effect of a monolayer thick SiN film on the surface states of the AlN/GaN heterostructure grown by molecular beam epitaxy was investigated. It was revealed that the submonolayer SiN coating of the AlN surface leads to the formation of an ordered (√3 × √3)R30° structure. Further SiN film growth results in a Si-enriched SiN amorphous film formation. The Fermi level, pinned 1 eV above the valence band maximum of as-grown AlN, jumps 2.3 eV when (√3 × √3)R30° is formed, and then gradually goes to 3.1 eV with an increase in the thickness of the SiN film up to 4 monolayers. The motion of the Fermi level is a consequence of the evolution of surface states, as well as the appearance of donor-like states in a Si-enriched SiN film. The presence of donor-like states was confirmed when studying the effect of current collapse in enhancemet-mode HEMTs made of SiN/AlN/GaN heterostructures.

The aim of the work is to create a miniature pulse optical emitter on an infrared laser diode with a pulse duration of the order of 1 ns and a pulse power of more than 30 W based on the effect of high-efficiency avalanche switching in bipolar silicon transistors. An optical emitter that can improve the accuracy of optical radar operation up to 10 times and which is a record indicator has been developed. The ways of increasing the radiation power, increasing the repetition rate of pulses (necessary to improve the accuracy of the radar), and searching for ways to transition to the subnanosecond region are considered.

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.

cited By 9; International audience; The numerical simulation, and theoretical and experimental optimization of field-effect microwave high-electron-mobility transistors (HEMTs) based on GaN/AlN/AlGaN heterostructures are performed. The results of the study showed that the optimal thicknesses and compositions of the heterostructure layers, allowing high microwave power implementation, are in relatively narrow ranges. It is shown that numerical simulation can be efficiently applied to the development of microwave HEMTs, taking into account basic physical phenomena and features of actual device structures.

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.

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.

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 peracetate of 7-(2-acetamido-2-deoxy-β-D-glucopyranosyloxy)-2-methyl-6-propyl-3′,4′-trimethylenedioxyisoflavone was synthesized under phase-transfer catalysis conditions by quaternary ammonium salts at room temperature and with heating to 50°C in K2CO3 solution (0.18 M):CHCl3. The corresponding glycoside of N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP) was synthesized from the peracetate.

A series of 7-O-β-D-glucosaminides of isoflavone derivatives were synthesized by glycosylation of phenolic hydroxyls using solid K2CO3:CH3CN with crown-ether catalysis and K2CO3 solution (0.18 M):CHCl3 with tetrabutylammonium-bromide catalysis.

We have fabricated a grating-gate InGaAs/GaAs field-effect transistor structure with narrow slits between the grating gate fingers. The resonant photoconductive response of this structure has been measured in the sub-terahertz frequency range. The frequencies of the photoresponse peaks correspond to the excitation of the plasmon resonances in the structure channel. The obtained responsivity exceeds the responsivity reported previously for the grating-gate FET detector with wider slits of the grating-gate by two orders of magnitude due to enhanced coupling between incoming terahertz radiation and plasmon oscillations in the slit-grating-gate field-effect transistor structure.

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.

Blue-green InGaN/GaN light-emitting diodes (LEDs) with spatially nonuniform current injection were fabricated and tested. Broad electroluminescence (EL) spectra with equal peak intensities of blue and green emission lines and shallow trough between them were observed at elevated injected current. These features of EL-spectrum are believed to be caused by the mesh-like patterning of the electrode as it creates spatially nonunform electric potential which provides spatial modulation of the injected current along the QW-planes. The latter results not only in spatial nonuniformity of intensity of generated light along the QW-planes but due to screening of polarization field in the QWs causes also position-dependent blue shift of EL. The observed phenomenon can be used to control the EL spectra of dual-wavelength LEDs by the patterned electrodes.

The results of numerical simulation and experimental study of the effect of the gate region parameters on static characteristics of microwave field-effect transistors based on pseudomorphic AlGaAs-InGaAs-GaAs heterostructures (p-HEMT) are considered. The possibility of correct simulation of static characteristics of actual device structures of p-HEMT transistors using the TCAD software package (SILVACO Inc.) is demonstrated. The essential necessity of using selective gate-groove etching to achieve controllable and reproducible device parameters is shown.

The depth distribution of free carriers over the HEMT structures with quantum-well layers is studied by electrochemical capacitance-voltage profiling. It is shown that the actual distribution of the concentration of free carriers and their energy spectrum in the HEMT structure channel can be obtained by numerical simulation of the results of profiling based on the self-consistent solution of one-dimensional Schrodinger and Poisson equations.

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...

N-Acetylmuramyl- l -alanyl- d -isoglutamine or muramyl dipeptide is a cleavage product of peptidoglycan by lysozyme. This study explored the use of the temperature-programmed desorption mass spectrometry (TPDMS) in analysis of glycoside of muramyl dipeptide: O-{(4-tert-butylcyclohexyl)-2-acetamido-2,3-dideoxy-β- d -glucopyranoside-3-yl}- d -lactoyl- l -alanyl- d -isoglutamine (MDP) on the surface of fumed silica. Stages of pyrolysis of MDP in condensed state and on the silica surface have been determined. Three stages have been clear identified under pyrolysis of MDP on the silica surface. Kinetic parameters of thermal reactions on the fumed silica surface and in the condensed state have been calculated.

Terahertz photoresponse of a GaAs/InGaAs transistor structure with large-area slit grating gate has been measured. Peaks in the photoresponse curve are assigned to plasmon resonances excited in the structure. More effective excitation of plasmon resonances is achieved in a grating gate structure with narrow slits, which increase the photoresponse amplitude by an order of magnitude.