卷 53, 编号 12 (2019)

The results of studies of nominally undoped epitaxial p-GaSb layers grown by metal–organic vapor-phase epitaxy at a ratio TMSb/TEGa in the range from 1 to 50 are reported. At the ratio TMSb/TEGa = 50, GaSb epitaxial layers, whose resistivity is 400 Ω cm, are produced. It is shown that, for such layers, the crystal quality assessed by several methods remains comparable to the quality of n-GaSb substrates used for the growth of nominally undoped GaSb layers.

Low frequency noise is studied in 4H-SiC power metal-oxide-semiconductor field-effect transistors (MOSFETs) irradiated with 15-MeV protons. Irradiation is carried out at room temperature in the frequency range from 1 Hz to 50 kHz upon irradiation with doses Φ of 10¹² to 6 × 10¹³ cm^–2. The frequency dependence of the spectral noise density S_I follows the law S_I ∝ 1/f with good accuracy. A correlation between the saturation current of the output characteristic I_d(V_d) and the low-frequency noise level is traced. At doses in the range 10¹² cm^–2 ≤ Φ ≤ 6 × 10¹³ cm^–2, the saturation current varies within about 20%, whereas the noise level changes by two orders of magnitude. The results of noise spectroscopy are used to estimate the trap density in the gate oxide, N_tv. In unirradiated structures, N_tv ≈ 5.4 × 10¹⁸ cm^–3 eV^–1. At Φ = 6 × 10¹³ cm^–2, N_tv increases to ~7.2 × 10¹⁹ cm^–3 eV^–1.

The impurity energy spectrum of undoped n-type GaAs, InAs, CdSnAs₂, CdGeAs₂, and CdTe, ZnO bulk crystals is studied based on a quantitative analysis of the baric and temperature dependences of the kinetic coefficients. It is found that the deep-level donor center corresponds to the intrinsic vacancy defect in the anion sublattice in the above-listed semiconductors. The conclusion on the nature of the donor center, i.e., the vacancy in the anion sublattice, is based on the fact that, in contrast to shallow impurity centers which trace the intrinsic band under uniform pressure, to which they are genetically related, the energy of deep impurity centers with respect to absolute vacuum remains constant under isotropic compression of the lattice. Therefore, it seems favorable to study the evolution of the carrier energy spectrum in semiconductors under uniform-pressure conditions. The energy-level positions with respect to the conduction-band edge and pressure coefficients of the energy gaps between them and the corresponding conduction-band bottom are determined. The shift of the energy level of the deep donor center to the conduction-band depth with decreasing band gap is observed.

MnAgIn₇S₁₂ single crystals 16 mm in diameter and ~40 mm in length are grown by planar crystallization of the melt. It is shown that the material grown crystallizes with the formation of the cubic spinel structure. From the transmittance spectra recorded in the region of fundamental absorption in the temperature range 10–320 K, the band gap E_g of the single crystals and its temperature dependence are determined. The dependence has a shape typical of most semiconductor materials: as the temperature is lowered, the band gap E_g increases. A calculation is carried out, and it is shown that the calculated values are in agreement with the experimental data.

The effect of temperature on the photoconductivity and its spectral dependence for thin films of organometallic CH₃NH₃PbI₃ perovskite is studied. The measurements performed at temperatures below room temperature reveal the features of the change in the photoconductivity with temperature in the region of the phase transition from the tetragonal to orthorhombic structure (140–170 K). On the basis of analysis of the effect of temperature on the nature of the change in the spectral dependences of the photoconductivity in the phase-transition region, mechanisms are proposed, which clarify the observed change in the photoconductivity.

A series of undoped GaAs/Al_xGa_{1 –x}As multiple quantum well heterostructures, whose doped analogs are used for the production of photodetectors operating in the spectral range 8–12 μm, is fabricated by molecular-beam epitaxy. For the heterostructures, the spectral position of absorption lines corresponding to the allowed transitions between quantum-confined electron and hole levels in GaAs layers is established. The influence of impurity–defect states on the luminescence and absorption spectra of quantum wells is studied. The excitonic corrections for the allowed transitions are determined in relation to the quantum-well width and the aluminum content in the barrier layers. The role of excitonic effects in restoring the structure of single-electron states from interband-absorption spectra (luminescence-excitation spectra) and the relationship between these states and the working region of IR photodetectors based on GaAs/Al_xGa_{1 –x}As quantum wells are discussed.

This work presents the fabrication and investigation of the multiwalled carbon nanotubes (MWCNTs) and graphene pristine powders based multifunctional pressure, displacement and gradient of temperature sensors. The effect of pressure on the resistance, Seebeck coefficient , thermoelectric voltage and current of the sensors was measured by changing pressure from 0 to 1.65 kgf/cm², while the effect of temperature gradient on the resistance, thermoelectric voltage and current of the sensors was measured up to the temperature gradient of 34–36°C. Dependence of the resistance on longitudinal compressive displacement up to 100 μm was investigated. It was found that the resistance, Seebeck coefficient and thermoelectric voltage of the CNT and graphene powders decreased with increasing pressure, while the thermoelectric current increased with pressure. Moreover, with increasing temperature gradient and average temperature a considerable increase was observed in thermoelectric current and voltage, while the increase in resistances was moderate. The increase in longitudinal displacement resulted in the compression of the samples that caused to decrease the resistances of the samples, especially in the case of samples made from CNT and graphene both. The simulation of the experimental results was carried out by using of linear functions and the results of simulations were in good agreement with experimental results.

The observation of de Haas–van Alphen oscillations when studying the silicon nanostructure at room temperature in weak magnetic fields enables the use of thermodynamic relations to calculate the density of states at the Fermi level at critical values of external magnetic-field strengths for integer filling factors.

The effect of samarium doping on the local structure and morphological features of the surface of a Se₉₅Te₅ chalcogenide glassy semiconductor film is investigated by X-ray diffraction analysis and atomic force microscopy, and the effect of doping on the current flow through Al–Se₉₅Te₅〈Sm〉–Te structures is examined by measuring the I–V characteristics in the steady-state mode. The results obtained are interpreted using Lampert’s theory of injection currents, the Elliott void-cluster model, and the Mott and Street charged defects model proposed for chalcogenide glasses.

The heat-conduction equation describing the current cord in a semiconductor is approximately solved for a Ge–Sb–Te semiconductor system of cylindrical configuration. It is shown that the cord current at infinitely long times is proportional to the squared maximum temperature at the cord center and inversely proportional to the applied electric field. The scale of the lateral current perpendicular to the main cord current is estimated. It is found that the lateral current is low in comparison with the cord current; hence, the formation of lateral cords growing from the main cord is highly improbable.

Single-phase cubic Pb_{1 –x}Ag_xS limited solid solutions based on PbS with a metal sublattice doped with Ag are produced. The maximal relative content of Ag in the Pb_{1 –x}Ag_xS solid solutions reaches up to x = 0.15. The thermal expansion of semiconductor Pb_{1 –x}Ag_xS solid solutions is first measured by the dilatometry technique in the temperature range from 295 to 580 K. The replacement of Pb atoms by Ag atoms in Pb_{1 –x}Ag_xS results in a decrease in the coefficient of thermal expansion, which is due to a change in the anharmonicity of atomic vibrations and a slight increase in the elastic properties. For single-crystal PbS particles and Pb_{1 –x}Ag_xS solid solutions, the spatial distributions of the modulus of elasticity E, the Poisson ratio μ, and the linear compressibility β in relation to the (hkl) direction are determined. The reflectance spectra of synthesized PbS, Ag₂S, and Pb_{1 –x}Ag_xS powders are recorded, and it is shown that the replacement of Pb by Ag in PbS is accompanied by an increase in the band gap.

The conductivity of single layer and bilayer graphene ribbons 0.5–4 μm in width fabricated by oxygen plasma etching is studied experimentally. The dependence of the electron concentration in graphene on the ribbon width is revealed. This effect is explained by the edge doping of graphene due to defects arranged in SiO₂ near the ribbon edges. The method of the formation of abrupt p–n junctions in graphene and structures with a constant electron concentration gradient in the graphene plane with the help of edge doping is proposed.

The results of investigating the wettability of commercial multi-walled carbon nanotubes (MWCNTs) Taunit-MD under irradiation with 120-keV Ar⁺ ions with various fluences are presented. The structure of the irradiated MWCNTs is investigated using Raman spectroscopy, scanning electron microscopy, and X-ray microanalysis of the samples. The dependences of the average diameter of the MWCNTs, the O₂ concentration, and defects in the MWCNT samples on the irradiation fluence, as well as their effect on the wettability with distilled water, ethylene glycol, and cyclohexane are considered. The possibility and prospects of using ion-beam modification methods for controlled variation of the wettability with the aim of creating a MWCNT coating, which is hydrophobic or hydrophilic to various types of liquids, are discussed.

The broad range of possibilities for optimizing the design and electrical parameters of crystals of Schottky diodes, manufactured according to the mesa–substrate and mesa–mesa planar technologies with anode terminals in the form of an air bridge with a whisker, along with the use of higher quality compact models, make it possible to efficiently exploit the physical potential of Schottky contacts when designing monolithic integrated circuits according to diode technologies, increase their reliability, and overcome the significant lag of semiconductor electronics behind optoelectronics in the terahertz (THz) frequency range.

The possibility of using lateral Ga(In)AsP nanostructures grown by the catalytic method in a quasi-closed volume from phosphorus and indium vapors on the GaAs (100) surface as an antireflection coating for photovoltaic devices is considered for the first time. It is shown that, at a fixed growth temperature, it is possible to control the surface morphology by changing the growth duration. The surface morphology is examined by scanning electron and atomic force microscopies. It is shown that the antireflection properties of the surface in the range 400–800 nm are related to its structure. The use of such a coating in GaAs-based photocells demonstrated a significant increase in the external quantum yield of photovoltaic converters.

Uniform thin films of amorphous and microcrystalline silicon are obtained within the forevacuum range of pressures by the gas-jet plasma-chemical method with the activation of gas by an electron beam. The effect of the flow rate of the carrier gas argon, the concentration of monosilane, the pressure in the reaction chamber, material of the substrate, and value of the current of the activating electron beam on the rate of deposition, photosensitivity, and crystallinity of the layers of silicon is investigated. For the amorphous silicon films, deposition rates of >1 nm/s are achieved, and for layers with a crystallinity exceeding 60%, the rate of deposition exceeded 0.6 nm/s. It is found that the substrate material does not have an effect on the structure of the deposited layers of silicon and the rate of their deposition.

The phase diagrams of the In_xAl_{1 –x}N solid solutions and conditions for their growth by magnetron sputtering and molecular beam and metalorganic vapor phase epitaxy are analyzed. The mutual equilibrium solubility in a wide range of compositions of the thick solution layers is near zero. Elastic misfit stresses in the In_xAl_{1 –x}N thin layers narrow the unstable immiscibility gap. By optimizing the growth conditions, one can obtain high-quality homogeneous In_xAl_{1 –x}N films for fabricating barrier layers in InAlN/GaN high electron mobility transistors.