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An algorithm for solving exciton Schrodinger equation in an arbitrary 2D multiple quantum well structure under applied electric field is proposed, allowing one to model both the absorption and refraction spectra consistently and efficiently. It gives much better quantitative results than variational approximation, while being faster than more advanced methods. The algorithm is implemented using R language and tested by comparing to other published results. Possible improvements are discussed.

The strong effect of weak interband illumination on tunneling transport in doped GaAs/AlAs superlattices was found under conditions of electric domain formation. The photoresponse at voltages below the threshold one (before the domain formation) did not observe. The phenomenon is referred to strong carrier depletion inside the triangular high-field domain. The domain modes transformations under the illumination were also found.

The design and technological conditions for the manufacture of photoconductive antennas based on low-temperature gallium arsenide (LT-GaAs) have been developed. The optimized photoconductive THz antenna is made based on LT-GaAs with the flag geometry of the contacts and with the interdigitated structure including metal closing through the dielectric of each second period. LT-GaAs samples were obtained by molecular beam epitaxy at temperatures of 210 °C, 230 °C, 240 °C on GaAs substrates (100). Dark and photocurrent were measured depending on the bias voltage of the LT-GaAs heterostructure at the EP6 probe station. Full wave finite element method solver has been used to investigate the proposed plasmon PCA electrical and optical behavior by combining the Maxwell's wave equation with the drift-diffusion/Poisson equations.

A material in the form of a multilayer structure based on low-temperature LT-GaAs grown on (111)A-oriented substrates is proposed for fabrication of THz photoconductive antennas. These structures contain active LT-GaAs layers and doping acceptor GaAs:Si-based layers. At the optical pump power of 19 mW and the bias voltage of 30 V, a photoconductive antenna based on the optimized {LT-GaAs/GaAs:Si} (111)A structure emits THz pulses with the average power of 2.3 μW at the pulse repetition frequency of 80 MHz; the conversion efficiency is 1.2 × 10–4. It is shown that the dependence of the integral power of THz pulses of the antenna based on the {LT-GaAs/GaAs:Si} (111)A structure on the applied voltage is superlinear; the dependence of this parameter on the optical pump power is plotted as a curve with saturation. It is shown that the designed antennas have a practical application in THz spectroscopy of biological solutions.

The structural characteristics of {InGaAs/InAlAs} superlattices, grown by molecular-beam epitaxy (MBE) at a temperature of 200°C on InP substrates with the crystallographic orientations (100) and (111)A, have been investigated. The superlattices consist of 100 periods of alternating In0.53Ga0.47As and In0.52Al0.48As layers with nominal thicknesses of 12 and 8 nm, respectively. The structural quality of the samples has been investigated by transmission electron microscopy (TEM). It is shown that the superlattice on the InP(100) substrate is single-crystal with high concentration of stacking faults, twins, and small-angle domains. The superlattice on the InP(111)A substrate is polycrystalline; however, the grown layers can be traced throughout almost the entire superlattice. A wave-like curvature of the layers grown on the InP(111)A substrate is much larger than that of the layers grown on the InP(100) substrate: the angular ranges of layer deviation from the horizontal growth plane reach ±30° and ±18°, respectively.

This work presents a process design kit (PDK) for a 0.15 μm GaAs pHEMT process for low-noise MMIC applications developed for AWR Microwave Office (MWO). A complete set of basic elements is proposed, such as TaN thin film resistors and mesa-resistors, capacitors, inductors, and transistors. The developed PDK can be used in technology transfer or education.

The morphology, chemical composition, microstructure, and electrical properties of BC3 thin films subjected to melting by a nanosecond laser pulse are investigated. The original films have been created by pulsed laser codeposition of B and C onto a sapphire substrate at 150 and 350°C. Morphological changes in the films depended on their initial structural state. However, a “frozen” structure of both films after irradiation corresponded to the B-saturated graphite-like phase, the local composition of which varied due to the formation of inclusions of amorphous boron carbide. Before and after irradiation, the films exhibited a slightly decreasing dependence of the surface resistance with increasing temperature from 4.2 to 330 K. After laser irradiation, the films resistance has decreased by a factor of ~2.6.

In most cases researchers consider existing de-embedding techniques in terms of characterization accuracy of the monolithic microwave integrated circuit component where an emphasis is put on the upper limit of the frequency range. In real practice, when faced with a choice of the de-embedding technique, one must take into account a number of additional factors, such as target application field of the component, manufacturing capabilities and production costs. In this paper we compare existing de-embedding techniques in the context of GaAs pHEMT-based two-stage low-noise amplifier monolithic microwave integrated circuit design. Firstly, we analyze several de-embedding techniques valid for pHEMTs with both coplanar and microstrip accesses and outline differences in de-embedded active bias S-parameters. Then, for each of the considered de-embedding technique we estimated the overall effect on low-noise amplifier small-signal characteristics, the total wafer area occupied by various de-embedding structures and flexibility of a technique regarding characterization of several active and passive devices with different pad distance and feed line length located on the same wafer.

Semiconductor quantum dots (QDs) are known for their high two-photon absorption (TPA) capacity. This allows them to efficiently absorb infrared photons with energies lower than the bandgap energy. Moreover, TPA in QDs can be further enhanced by the interaction of excitons of the QDs with plasmons of a metal nanoparticle. We fabricated nonlinear plasmon–exciton photodetectors based on QDs and silver nanoplates (SNPs) to demonstrate the optoelectronic application of these effects. A thin layer of CdSe QDs was used as a source of charge carriers for a photoresistor-type photodetector. SNPs with near-infrared plasmon modes were introduced into the layer of QDs to increase the light absorption efficiency. Under near-infrared irradiation, the power of the dependence of the photocurrent on the excitation intensity was twice the power of the corresponding dependence under one-photon excitation with visible light. This proved that the new photodetector efficiently operated under two-photon excitation. Although the SNP light absorption was linear, energy was transferred from plasmons to excitons in the two-quantum mode, which led to a nonlinear dependence. Moreover, we found that the photocurrent from the designed photodetector containing the QD–SNP composite was an order of magnitude higher than that from a photodetector containing QDs alone. This can be explained by the plasmon-induced increase in the TPA efficiency., This study was supported by the Russian Science Foundation, grant no. 18-72-10143. The part of this study dealing with the synthesis and characterization of nanomaterials was supported by the Russian Science Foundation, grant no. 18-19-00588. V. K. has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie, grant agreement no. 101025664 (QESPEM). I. N. acknowledges support of the French National Research Agency (ANR-20-CE19-009-02) and co-funding by the European Union via the European Regional Development Fund (FreeBioWave project).

Metamorphic high-electron-mobility transistor (HEMT) structures based on deep In0.2Ga0.8As/In0.2Al0.8As quantum wells (0.7 eV for Γ electrons) with different metamorphic buffer designs are implemented and investigated for the first time. The electronic properties of metamorphic and pseudomorphic HEMT structures with the same doping are compared. It is found that, over a temperature range of 4–300 K, both the electron mobility and concentration in the HEMT structure with a linear metamorphic buffer are higher than those in the pseudomorphic HEMT structure due to an increase in the depth of the quantum well. Low-temperature magnetotransport measurements demonstrate that the quantum momentum-relaxation time decreases considerably in metamorphic HEMT structures because of enhanced small-angle scattering resulting from structural defects and inhomogeneities, while the dominant scattering mechanism in structures of both types is still due to remote ionized impurities.

Relatively low and high deposition rates of BCх films were realized by pulsed laser ablation of mixed B–diamond and dual B–graphite targets, respectively. Deposition was performed at 500 °C and the rate of film deposition was determined with respect to the number of atomic monolayers (obviously less or more than one monolayer) grown for one laser pulse. In the case of BCх films formation with a low deposition rate, doping with B facilitated the growth of the nanocomposite structure, which possessed an increased fraction of sp3 bonds, a very low electrical resistance, and an improved mechanical performance. The change of the sheet resistance of these films as the temperature was reduced from 300 to 65 K had a metallic character. For about 95-nm-thick films with bulk compositions of BC1.7 and BC0.6, the resistivity at room temperature were approximately equal to 1.5 mΩ·cm, and the lowest resistivity of 0.23 mΩ·cm was detected for B-enriched film at 85 K. With an increase in the B atom concentration in such films, the charge carrier (holes) concentration decreased, and their mobility increased from 180 to 10,500 cm2·V−1·s−1 due to samples cooling. The application of a higher deposition rate from the dual B–graphite target activated surface migration of condensed atoms, which caused the development of granular morphology, the B segregation and the reduction of the sp3 bond fraction. The hardness and electrical conductivity of such films were obviously inferior to those of the films obtained by PLD with a low deposition rate.

The experiments showed the strong dependence of forward and backward scattering of light in the visible region of the spectrum by silicon nanoparticles on the method of their preparation. Silicon nanoparticles are created in two ways: by laser ablation and by the action of a relativistic electron beam. The backscattering spectra from the obtained silicon nanoparticles were measured. Raman light scattering is much more intense for silicon nanoparticles obtained by an electron beam as compared to those created by laser radiation and from single-crystal silicon. These properties of silicon nanoparticles should be taken into account when creating nanoantennas, metamaterials, and other nanophotonic devices with low dissipative losses and reflection.

The active region of a THz (terahertz) quantum-cascade laser based on three tunnel-coupled GaAs/Al0.15Ga0.85As quantum wells with a resonance-phonon depopulation scheme is designed. Energy levels, matrix elements of dipole transitions, and gain spectra are calculated as functions of the applied electric-field strength F and temperature. It is shown that the maximum gain is implemented at a frequency of 3.37 THz and F = 12.3 kV/cm. Based on the proposed design, a quantum-cascade laser emitting at ~3.3 THz with a double metal waveguide and Tmax ~ 84 K is fabricated. The activation energy Ea = 23 meV for longitudinal-optical (LO) phonon emission upon the stimulated recombination of hot electrons from the upper laser level to the lower one is determined from the Arrhenius temperature dependence of the output power.

In this paper, we report on the results of the study of the Ti/Au/n-GaAs planar Schottky diodes (PSD) intended for the wideband detection of terahertz radiation. The two types of the PSD devices were compared having either the dual n/n+ silicon dopant profile or the triple one with a moderately doped matching sublayer inserted. All the diodes demonstrated no noticeable temperature dependence of ideality factors and barrier heights, whose values covered the ranges of 1.15–1.50 and 0.75–0.85 eV, respectively. We observed the lowering of the flat band barrier height of ∼80 meV after introducing the matching sublayer into the GaAs sandwich. For both the devices types, the series resistance value as low as 20 Ω was obtained. To extract the total parasitic capacitance, we performed the Y-parameters analysis within the electromagnetic modeling of the PSD's behavior via the finite-element method. The capacitance values of 12–12.2 fF were obtained and further verified by measuring the diodes' response voltages in the frequency range of 400–480 GHz. We also calculated the AC current density distribution within the layered structures similar to those being experimentally studied. It was demonstrated that insertion of the moderately Si-doped matching sublayer might be beneficial for implementation of a PSD intended for the operation within the ‘super-THz’ frequency range.

The influence of the concentration of δ doping with Si on the electron transport properties of Al0.25Ga0.75As/In0.2Ga0.8As/GaAs pseudomorphic quantum wells is studied in a broad temperature range of 4.2–300 K. A decrease in the doping efficiency at an electron concentration of >1.8 × 1012 cm–2 is found. This is caused by the effects of incomplete impurity ionization, which is also reflected on the temperature dependence of the electron concentration. A nonmonotonic variation in the electron mobility with increasing donor concentration, which is not associated with filling of the upper subband of size quantization, is observed. An increase in the mobility is associated with a rise in the Fermi momentum and screening, while its subsequent drop with increasing Si concentration is caused by the tunnel degradation of the spacer layer with a decrease in the conduction-band potential in the region of the δ-Si layer.

The influence of the concentration of silicon donors on the electron-transport properties of pseudomorphous Al0.25Ga0.75As/In0.2Ga0.8As/GaAs quantum wells (QWs) in heterostructures with heavy unilateral δ-doping by Si atoms was studied in a broad temperature interval (2.1–300 K). High electron mobility (up to 35700 cm2/(V s)) at T = 4.2 K was observed at a 2D (sheet) electron density of 2 × 1012 cm–2 in the QW. A band mechanism limiting the ionization of donors at an increased level of doping is described. The nonmonotonic variation of electron mobility with increasing silicon concentration is explained. A growth in the mobility is related to increase in the Fermi momentum and screening, while the subsequent decay is caused by tunneling-induced degradation of the spacer layer with decreasing potential of the conduction band in the region of δ-Si layer. It is shown that the effect is not related to filling of the upper subband of dimensional quantization.

We investigate the influence of the surface properties of a low-temperature-grown GaAs photoconductive antenna on the terahertz (THz) response power. A comparison to the surface roughness which is extracted from an atomic force microscope is given. We used energy dispersive x-ray spectroscopy (EDX) measurements to determine the Ga/As compositional ratio in the LT-GaAs.

The electron-transport and optical properties of heterostructures with a surface InGaAs/InAlAs quantum well in the cases of inverted δ doping with Si atoms (below the quantum well) and of standard δ doping (above the quantum well) are compared. It is shown that, in the case of inverted doping, the two-dimensional electron density in the quantum well is increased in comparison with the case of the standard arrangement of the doping layer at identical compositions and thicknesses of other heterostructure layers. The experimentally observed features of low-temperature electron transport (Shubnikov–de Haas oscillations, Hall effect) and the photoluminescence spectra of heterostructures are interpreted by simulating the band structure.

The efficiency of the generation and detection of terahertz radiation in the range up to 3 THz by LT-GaAs films containing equidistant Si doping δ layers and grown by molecular beam epitaxy on GaAs (100) and (111)Ga substrates is studied by terahertz spectroscopy. Microstrip photoconductive antennas are fabricated on the film surface. Terahertz radiation is generated by exposure of the antenna gap to femtosecond optical laser pulses. It is shown that the intensity of terahertz radiation from the photoconductive antenna on LT-GaAs/GaAs (111)Ga is twice as large as the intensity of a similar antenna on LT-GaAs/GaAs(100) and the sensitivity of the antenna on LT-GaAs/GaAs (111)Ga as a terahertz-radiation detector exceeds that of the antenna on LT-GaAs/GaAs(100) by a factor of 1.4.

It was investigated the thermal stability of two types of Hall sensors based on gold nanofilms deposited on sapphire: (i) with the titanium adhesive sublayer (Ti/Au) and (ii) with the titanium adhesive sublayer and the platinum barrier sublayer of (Ti/Pt/Au). Vacuum annealing for 3 h at 400 °C significantly changes all investigated electrophysical parameters of samples with the Ti/Au metallization, which is explained by the titanium diffusion into gold. At the same time, the sensitivity and the resistivity of sensors with the Ti/Pt/Au metallization remain unchanged within a few percent, allowing them to be used in the plasma's magnetic diagnostic systems of the ITER and DEMO fusion reactors where operating temperatures will exceed 300 °C.

Using the Shubnikov–de Haas effect, the dependences of electron effective mass m* and transport and quantum momentum relaxation times in Al0.25Ga0.75As/In0.2Ga0.8As/GaAs pseudomorphic quantum wells with one-sided silicon δ-doping on the electron density in the range of (1.1–2.6) × 1012 cm–2 have been established. Nonparabolicity coefficient m* in the linear approximation was found to be 0.133m0/eV. Both the transport and quantum momentum relaxation times depend nonmonotonically on Hall electron density nH, which is related to the competition between growth mechanisms of the Fermi momentum and the increasing contribution of large-angle scattering with increasing donor concentration.

The spectra of mode loss in terahertz quantum cascade laser (THz QCL) with double metal waveguide (DMW) based on Au, Cu and Ag have been analysed. On the basis of measurements of the resistivity of DMW claddings for the temperature range from 4.2 to 300 K, the loss coefficients of THz radiation at Au-, Cu-, Ag-claddings are calculated. We show that the Ag-based DMW allows to reduce the losses by 1.3–7.0 cm-1 in comparison with Au-based DMW at room temperature. Our calculations show that the Ag-based DMW has slightly lower losses (~1 cm-1) than Cu-based DMW at cryogenic temperatures (below 100 K). The use of Cu-based DMW allows to reduce the loss coefficient in comparison with Ag-based DMW at higher temperatures (above 100 K). Temperature dependence of threshold gain for THz QCL with Au-, Cu-, Ag-based DMW are calculated. Taking into account the absorption of THz radiation by free carriers and optical phonons, the spectrum of total mode loss of THz QCL with different thickness of n+-GaAs top contact layer are analyses.

The problem of modelling the absorption coefficient and refractive index spectra of III-V heterostructures with multiple quantum wells and superlattices under applied electric field is considered. This is a crucial step in the design of efficient and compact electro-optic modulators. The goal of this work is to find a simple, fast and reliable method to qualitatively compare various heterostructure designs. Which is why two-band effective mass approximation is used here. The paper contains comparison of existing methods as well as some new results.

The dependence of electron transport properties of two-dimensional electron gas on sheet doping concentration in one-sided δ-doped pseudomorphic Al xGa1-xAs/In0.2Ga0.8 As/GaAs quantum wells is investigated. The wide range of silicon dopant sheet concentrations of (1.6–16) · 10 12 cm−2 is investigated. Electron effective masses, nonparabolicity and scattering times are determined by low-temperature Shubnikov-de Haas effect measurements. The dependence of the quantum and transport relaxation times on nH is shown to have nonmonotonic character due to the competition of the Fermi momentum increase and the large angle scattering due to the variation of ionized donor concentration. The nonparabolicity coefficient in the In0.2Ga0.8As quantum well is determined to be 0.68 1/eV.

The effect of pulsed laser annealing (PLA, i.e., action of nanosecond laser pulses in air atmosphere) on surface morphology, structure, chemical state, and electrical properties of thin films consisting of boron and carbon atoms was studied. The nanolayered В/С and mixed ВСx~3 thin film precursors (with a thickness ~110–140 nm) were created on sapphire substrates by using the pulsed laser deposition. Scanning electron microscopy and Raman scattering measurements indicate that the process of stratification of the multilayer B/C films dominated during PLA of the films. The outer layers were removed, and closer to the substrate, the B and C layers were preserved, and they were not mixed. For the mixed ВСх films deposited at elevated temperatures, the PLA treatment enhances ordering of initially amorphous film structure. At the stage of melting of these films, oxygen (from surrounded air) penetrated inside the top layer of the film leading to the formation of a multiphase structure from g-BCx and B-doped GO/rGO after solidification. Studies of the chemical state of elements in the irradiated film have shown that О atoms, which penetrated the under-surface layers of the film, facilitated the formation of new chemical bonds in the B–C–O system. The concentration of O atoms in the depth of the film could reach 8%. The preferential oxidation of boron in a homogeneous mixture of B–C–O atoms indicated that intercalation of carbon matrix could be due to the incorporation of not only O atoms, but also B–O molecules. The laser irradiated ВСх films have a relatively low resistivity (~1.6 mΩ·cm) and semi-metallic dependence on temperature in the range 4.2–300 К. The spatial distribution of conductivity zones after PLA has an irregular structure, and its pattern looks like sand dunes, indicating that the PLA treatment leads to mixing zones of high with those of lower conductivity. The contact-tip resistivity inside the areas of high conductivity of the ВСx/Al2O3 samples may be significantly lower than that of pure graphite.

The longitudinal and Hall magnetoresistances are measured in the quantum Hall effect regime in the n-InGaAs/InAlAs heterostructures at temperatures of T = (1.8–30) K in magnetic fields up to B = 9 T. Temperature-induced transport in the region of the longitudinal resistance minima, corresponding to the plateau regions at Hall resistance, is investigated within the framework of the concept of hopping conductivity in a strongly localized electron system. The analysis of variable-range hopping conductivity in the region of the second, third, and fourth plateau of the quantum Hall effect provides the possibility of determining the localization length exponent.

A stack of five elastically strained metastable GeSn layers with a thickness of 200 nm each separated by Ge spacer layers with a thickness of 20 nm is grown on a (001) Si/Ge virtual substrate. The molar fraction of Sn in the GeSn layers is 0.005, 0.034, 0.047, 0.072, and 0.10. After growth the structure is subjected to thermal annealing for 2 min at a temperature of 400°C. It is demonstrated that during the course of annealing the GeSn alloy, along with plastic relaxation, undergoes phase separation; this phase separation begins before the end of plastic relaxation. The structural degradation of the GeSn layers increases with increasing concentration of Sn accumulated on the structure surface in the form of an amorphous layer.

This study is devoted to the search for new possibilities of characterizing crystal-structure features using high-resolution X-ray diffraction. The emphasis is on the scanning mode across the diffraction vector (ω-scanning), since researchers usually pay little attention to this mode, and its capabilities have not yet been completely revealed. For the [011] and [01 $$\bar 1$$ ] directions, the ω-peak half-width and the average tilt angle of the sample surface profile are compared. The diagnostic capabilities of X-ray scattering mapping are also studied. The objects of study are semiconductor nanoheterostructures with an InAlAs/InGaAs/InAlAs quantum well and an In x Al1–x As metamorphic buffer grown by molecular-beam epitaxy on InP and GaAs substrates. Such nanoheterostructures are used to fabricate microwave transistors and monolithic integrated circuits. The objects under study are more completely characterized using the Hall effect, atomic-force microscopy, and low-temperature photoluminescence spectroscopy at 79 K.

Low-temperature gallium arsenide (LT-GaAs) films were grown by the method of molecularbeam epitaxy (MBE) at a reduced temperature (230°C) on GaAs(100) substrates and subjected to postgrowth annealing in various regimes. Photoconductive antennas (PCAs) with flag geometry formed on the film surface were characterized by terahertz (THz) response power at various bias voltages. The method of THz spectroscopy was used to study the characteristics of PCAs based on LT-GaAs films annealed in various regimes and the optimum interval of postgrowth annealing temperatures (670–720°C) was established.

For an investigation of the quantum Hall effect on n-In0.85Ga0.18As/In0.82Al0.82As metamorphic nanoheterostructures with high InAs content the longitudinal and Hall magnetoresistances were measured in magnetic fields up to 9 T at T = ( 1.8 ÷ 30 ) K . The results for a temperature dependence of conductivity on the delocalized states at the center of Landau level were analysed within the scaling concept for a plateau-plateau transition in quantum Hall regime.

In this paper we report on the fabrication of a planar Schottky diode utilizing a Г-shaped anode suspended bridge. The bridge maintains transition between the top and bottom level planes of a 1.4 µm thick GaAs mesa. To implement the profile of a suspended bridge and inward tilt of a mesa wall adjacent to it, we make use of an anisotropic etching of gallium arsenide. The geometry proposed enables the fabrication of a diode with mesa of an arbitrary thickness to mitigate AC losses in the diode layered structure at terahertz frequencies of interest. For frequencies beyond 1 THz, it is also beneficial to use the geometry for the implementation of n-GaAs/n-InGaAs heterojunction Schottky diodes grown on InP substrate.

The electrophysical and structural properties of InAlAs/InGaAs/InAlAs quantum wells (QWs) with thin InAs inserts were investigated by means of Hall effect measurements and scanning transmission electron microscopy. The analyzed heterostructures are nearly the same ones using for high electron mobility transistors manufacturing except for heavily doped contact top layer. The increase of the electron mobility and concentration in the heterostructures with thin InAs layers in the center of the InGaAs QW as compared with the uniform QW was found and this effect strongly depended on the technological conditions during growth of the InAs inserts. The dependence of the InAs insert structural quality and heterointerface width on the As4 beam equivalent pressure PAs was revealed. The decreased PAs is required for obtaining uniform and smooth InAs inserts as opposed to higher PAs resulting in the interface spreading and lateral composition inhomogeneity of the InAs insert.

The photoluminescence spectra of modulation-doped InAlAs/InGaAs/InAlAs heterostructures with quantum wells containing thin strained InAs and GaAs inserts are investigated. It is established that the insertion of pair InAs layers and/ or a GaAs transition barriers with a thickness of 1 nm into a quantum well leads to a change in the form and energy position of the photoluminescence spectra as compared with a uniform In0.53Ga0.47As quantum well. Simulation of the band structure shows that this change is caused by a variation in the energy and wave functions of holes. It is demonstrated that the use of InAs inserts leads to the localization of heavy holes near the InAs layers and reduces the energy of optical transitions, while the use of GaAs transition barriers can lead to inversion of the positions of the light- and heavy-hole subbands in the quantum well. A technique for separately controlling the light- and heavy-hole states by varying the thickness and position of the GaAs and InAs inserts in the quantum well is suggested.

A complex investigation of structural and electrical properties of In0.52Al0.48As/In y Ga1 − y As/In0.52Al0.48As nanoheterostructures on InP substrates containing thin InAs and GaAs inserts in a quantum well (QW) has been performed. The GaAs nanolayers are grown at the QW boundaries between InGaAs and InAlAs layers, while the double InAs inserts are grown in InGaAs layers symmetrically with respect to the QW center. The layer and interface structures have been studied by transmission electron microscopy. It is shown that, when using the proposed epitaxial growth conditions, the introduction of ∼1.2-nm-thick InAs nanoinserts into the InGaAs QW and a ∼1-nm-thick GaAs nanobarrier at the QW boundaries does not induce structural defects. The diffusion of the InAlAs/InGaAs interface (2–3 monolayers) and InAs/InGaAs nanoinsert interface (1–2 monolayers) has been estimated. Measured Hall mobilities and electron concentrations in structures with different combinations of InAs and GaAs inserts have been analyzed using calculated energy band diagrams and electron density distributions. It is found that the photoluminescence spectra of the structures under study have differences caused by specific structural features of coupled QWs (specifically, the change in the In molar fraction due to InAs inserts and the change in the QW thickness due to GaAs transition barriers.

Samples of epitaxial structures with GaAs/AlGaAs quantum rings different in morphology are grown by droplet epitaxy. The photoluminescence spectra of the samples are recorded at temperatures of 20–90 and 300 K. Intense peaks defined by quantum confinement of the charge-carrier energy in the quantum rings are observed in the optical region. The peaks are identified by estimating the energy of the ground state of electrons and holes in GaAs quantum rings and by recording the spectra of the samples after removing the layers with the quantum rings by etching. The average dimensions of the quantum rings are determined by atomic force microscopy and scanning electron microscopy. Some inferences about the factors that influence the emission spectrum and intensity of the epitaxial structures with quantum rings are drawn.

The specific features of the photoluminescence and the electrical properties of doped nanoheterostructures containing a composite InAlAs/InGaAs/InAlAs quantum well with a thin InAs insert in the middle are studied. The insert thickness is varied in the range from 1.7 to 3.0 nm. It is established that the position of the peaks in the photoluminescence spectra in the photon energy range 0.6–0.8 eV correlates with the InAs insert thickness. Simulation of the band structure shows that the experimentally observed variation in the energy of optical transitions is associated with lowering of the energy of electron and hole states in the quantum well with increasing insert thickness. In the photon energy range 1.24–1.38 eV, optical transitions in the region of the InAlAs buffer-InP substrate interface are observed. The signal photon energy and intensity depend on the features of the formation of this heterointerface and on the conditions of substrate annealing. It is conceived that this is due to the formation of a transition region between the InAlAs buffer and the substrate.

The growth of GeSn layers by molecular-beam epitaxy on Si (100) wafers coated with a germanium buffer layer is investigated. The properties of the fabricated structures are controlled by reflection high-energy electron diffraction, atomic-force microscopy, X-ray diffractometry, Rutherford backscattering, and Raman scattering. It is shown that GeSn layers with thicknesses up to 0.5 μm and Sn molar fractions up to 0.073 manifest no sign of plastic relaxation upon epitaxy. The lattice constant of the GeSn layers within the growth plane is precisely the same as that of Ge. The effect of rapid thermal annealing on the conversion of metastable elastically strained GeSn layers into a plastically relaxed state is examined. Ge/GeSn quantum wells with Sn molar fraction up to 0.11 are obtained.

The gold and molybdenum nanofilms were used as a material for sensitive layers of the Hall type magnetic field sensors intended to conducting a long-term magnetic diagnostics of the systems with high radiation loads. An in situ testing of sensors based on the metal nanofilms had been carried out in the fluxes of reactor neutrons. It was shown that the nanofilms electrophysical characteristics remain unchanged up to neutron fluence of ∼ 1024 n/m2 at temperature of ∼ 130 deg. C.

This work reports on an advanced approach to the design of THz photoconductive. antenna (PCA). The LT-GaAs thin films used for the PCA fabrication were synthesized by MBE method on GaAs (100) substrate by adjusting the As pressure, As/Ga fluxes ratio, growth/annealing temperatures and annealing time. These parameters crucially affect electro-optical properties of the PCA samples as evidenced by the THz radiation power and time-domain spectroscopy measurements. The annealing temperature of 670 °C was found to be optimal for constructing a PCA possessing high amplitude of the THz radiation over the spectral range up to 1 THz at the resonance of 0.1 THz. The comparison of this PCA with the reference ZnTe crystal reveals a 2-fold increase in THz power. Furthermore, this antenna attains a 1.5-, 3-, and 2-fold increase in THz power, photocurrent efficiency, and actuating dc BV, as compared with the commercial ZOMEGA antenna. These results pave the way towards the creation of highly efficient LT-GaAs-based PCAs.

The effect of the hybridization of quantum states on electron transport in a two-barrier quantum well δ-doped through a spacer layer at the limit of heavy doping is shown theoretically and experimentally. A method for increasing the electron mobility in the quantum well by suppressing the tunnel coupling with the donor region through the introduction of an AlAs nanobarrier into the spacer layer is proposed. It is experimentally shown that, in the samples with a shallow quantum well, the AlAs nanobarrier introduced into the spacer layer provides a larger than threefold increase in the electron mobility at low temperatures.

The drop epitaxy process in the GaAs/AlGaAs system is experimentally and theoretically studied. Epitaxial structure samples with arrays of single and double quantum rings are grown under various growth conditions. Diffusion processes of Ga and As adatoms are considered, steady-state diffusion equations are analytically solved, and the formation mechanisms of single and double quantum rings are revealed. The results obtained make it possible to model the quantum ring profile depending on growth conditions and, hence, to control the nanostructure profile during drop epitaxy.