Volodymir N Poroshin

National Academy of Sciences of Ukraine | ISP · Institute of Physics

In this work, for the first time, both initial and secondary branches of hierarchical nitrogen-doped multi-walled carbon nanotubes (h-N-MWCNTs) were obtained using chemical vapor deposition due to the decomposition of ace-tonitrile over Co-based nanoparticles. The results of a study of the electrical conductivity of h-N-MWCNTs for a wide temperatur...

The effect of further thermal annealing in a hydrogen atmosphere on the electrical properties of hydrazine-reduced graphene oxide (RGO) was investigated. It was found that heat treatment significantly improves the conductivity of RGO and reduces the room temperature resistivity by ten times. The changes become even more significant at the temperatu...

We present the results of a study of the electrical properties of macroscopic free-standing reduced graphene oxide paper (RGOP) with a 60 % fraction of sp²‑carbons at liquid helium temperatures. Graphene domains form an array of quantum dots that determine material properties. At low temperatures, the electrical conductivity of the RGOP can be desc...

The transient processes in the electric conduction of fine disperse 2D-MoS2 powder samples, occurring at changing voltages applied to the sample under the conditions of uniaxial compression, have been studied. The long-term transient changes in conduction occurring both after switching on and off the applied voltage were observed. The current–volta...

The features of electric transport in the powder samples consisting of the nanosize 2D-MoS2 flakes with different number of layers have been studied under the conditions of uniaxial pressure. There have been measured current-voltage characteristics at the room temperature in the voltage range of 0 through 1.5 V at three magnitudes of the uniaxial p...

The electric conductivity behavior in the single and double tunnel-coupled quantum wells (QW) with different doping profile caused by the impact of short pulses of the strong longitudinal (in the quantum wells plane) electric field has been investigated. It is established that at low temperatures (4 K) after such an impact the long-term metastable...

The electric conductivity behavior in the single and double tunnel-coupled quantum wells (QW) with different doping profile caused by impact of short pulses of the strong longitudinal (in the quantum wells plane) electric field has been investigated. It is established that at low temperatures (4 K) after such impact the long-term metastable state w...

The features of electric transport in the powder samples consisting of the nanosize 2D-MoS2 flakes with different number of layers have been studied under the conditions of uniaxial pressure. There have been measured current-voltage characteristics at the room temperature in the voltage range of 0 through 1.5 V at 3 magnitudes of the uniaxial press...

The dependences of the current and integral intraband terahertz electroluminescence intensity on the electric field in the n-InGaAs/GaAs heterostructures with asymmetric double tunnel-coupled quantum wells under the conditions of bipolar lateral transport are established to differ qualitatively for different interwell barrier widths. In the case of...

The electrical conductivity of carbon nanocomposite TVO-series resistors used as temperature sensors are studied in a wide temperature range of 300–1.8 K. It is found that hopping conductivity emerges at temperatures below 77 K. The shape of its temperature dependence varies for resistors having different resistance at room temperature. Raman spect...

The model has been proposed for calculation of the electron transport via the double conducting channels formed in heterostructures with tunnel-coupled quantum wells with essentially different mobility of electrons. Experiments to test dependences of transport characteristics on temperature and electric field were carried out on heterostructures ba...

In this paper the gamma irradiation effect on graphene layers is investigated. A simple method of synthesis from a solid-source bilayer (SiC/Ni) precursor has been used for the production of graphene flakes, both single-layer and multilayer. Samples with graphene flakes on the Ni surface were subjected to gamma irradiation in vacuum and in air unde...

A study of how heating current carriers by a pulsed electric field impacts the conductivity and magnetoresistance of carbon composite TVO resistors in the liquid helium temperature range. It is found that heating the carriers in fields of up to 60 V/cm at T = 4.2 K decreases the magnetoresistance by approximately 4 times, while preserving a relativ...

We present the results of experimental and theoretical studies of the surface plasmon polariton excitations in heavily doped GaNepitaxial layers. Reflection and emission of radiation in the frequency range of 2–20 THz including the Reststrahlen band were investigated for samples with grating etched on the sample surface, as well as for samples with...

The interband and intraband radiation from the n-InGaAs/GaAs heterostructures with the double and triple tunnel coupled and selectively doped quantum wells (QWs), which is appeared under the lateral electric field and in the presence of hole injection from the anode contact, has been investigated. A steep increase of the interband radiation intensi...

The binding energy of an impurity delta layer situated either in the centre or at the edge of a quantum well (QW) is theoretically considered for the example of n-type Si0.8Ge0.2/Si/Si0.8Ge0.2 QW doped with phosphorus. Calculations are made for the case of not so big impurity concentrations, when impurity bands are not yet formed and it is still po...

The binding energy of an impurity delta layer situated either in the centre or at the edge of a quantum well (QW) is theoretically considered for the example of n-type Si 0⋅8 Ge 0⋅2 /Si/Si 0⋅8 Ge 0⋅2 QW doped with phosphorus. Calculations are made for the case of not so big impurity concentrations, when impurity bands are not yet formed and it is s...

Surface plasmon polaritons at the n-GaN/vacuum interface are investigated. Experimental studies of terahertz radiation reflection and emission are performed on heavily silicon-doped GaN epitaxial layers grown on sapphire substrates. To provide interaction of THz radiation with the surface plasmon polaritons, a regular grating was fabricated on the...

The results of investigations of the electric and magnetic transport phenomena of charge carriers in the heterostructures with quantum wells and impurity delta-layers in adjacent barriers are reviewed and analyzed. The positive magnetoresistance observed at low temperatures (T < 20 K) and the dependence of the charge carrier mobility on the impurit...

The lateral magnetoresistance of the multi-layer AlGaAs/GaAs/AlGaAs heterostructures with quantum wells and impurity δ-layers in the adjacent barriers has been studied at 4.2 K. It is shown that both the classical magnetoresistivity tensor components and the magneto-quantum effects in such structures considerably depend on the contribution to condu...

The infrared radiation emitted by hot electrons in n-InGaAs/GaAs quantum-well heterostructures subjected to a lateral electric field is investigated under conditions of carrier injection from the current contacts. In structures with double tunneling-coupled wells one of which is δ-doped, a pronounced increase in the intensity of far-infrared radiat...

Effects of tin doping on crystallization of amorphous silicon were studied using Raman scattering, Auger spectroscopy, scanning electron microscopy, and X-ray fluorescence techniques. Formation of silicon nanocrystals (2–4 nm in size) in the amorphous matrix of Si1-xSnx, obtained by physical vapor deposition of the components in vacuum, was observe...

Microstructure investigations of thin Si-Sn alloy films were carried out, by using Auger and Raman spectroscopies, X-ray fluorescence analysis, and electron microscopy. The films were produced by the thermal-vacuum coevaporation of Si and Sn. The properties of films with the Sn content ranging from 1 to 5 wt.% are studied. A significant influence o...

The photoconductivity kinetics in n-Inx Ga1 − x As/GaAs heterostructures with double-coupled quantum wells and δ doping of one of them has been experimentally studied under interband excitation. It is shown that the long-term photoconductivity decay observed in the temperature range from 10 to 70 K is due to the chaotic potential associated with co...

In the p-Si0.88Ge0.12/Si heterostructures with quantum wells delta-doped by boron, the decay kinetics of the lateral infrared photoconduction has been studied at low temperatures (15 to 50 K). Photoconduction was excited in the impurity spectral range by a CO2-laser pulse radiation. After switching off the light, both positive and negative residual...

The lateral transport of electrons in single- and double-well pseudomorphic GaAs/n-InGaAs/GaAs heterostructures with quantum wells 50–100 meV deep and impurity δ-layers in the wells, with concentrations in the range 1011 < N s < 1012 cm−2, has been investigated. Single-well structures with a doped well at the center exhibit a nonmonotonic temperatu...

The temperature-activated charge transport in disordered organic semiconductors at large carrier concentrations has been thoroughly considered, by using a recent analytical model [Phys.Rev.B 76, 045210 (2007)] assuming a Gaussian density-of-states (DOS) distribution and Miller–Abrahams jump rates. We demonstrate that the apparent Meyer–Neldel compe...

The influence of thermal ionization of an impurity delta-doped layer situated either in the center or on the edge of a quantum well (QW) on impurity binding energy is investigated theoretically for the case of Si0.8Ge0.2/Si QW. It is shown that the Hartree potential created by free electrons and by ionized impurities at high temperatures superimpos...

The drift of charge carriers in the p-Si 0.88 Ge 0.12 /Si heterostructures under strong lateral electric fields and conditions of carrier generation by the band-to-band light absorption has been investigated experimentally. The data of the drift length, drift mobility, and lifetime of charge carriers within the temperature range 20 to 77 K under th...

It is shown that the far-infrared radiation of electrons in the selectively doped heterostructures with double tunnel-coupled quantum wells in high lateral electric fields strongly depends on the level of doping of the wells. At a high impurity concentration in a narrow well, higher than (1−2) × 1011 cm−2, the radiation is caused only by indirect i...

Meyer-Neldel rule for charge carrier mobility was studied in C(60)-based organic field effect transistors (OFETs) fabricated at different growth conditions which changed the degree of disorder in the films. The energetic disorder in the films was found to correlate with a shift in the Meyer-Neldel energy, which is in excellent agreement with the pr...

The effective-medium approximation (EMA) analytical theory is advanced further to describe charge transport at arbitrary charge-carrier concentration in a disordered organic material with superimposed polaron effects. A key point of this model compared to the previous treatment [Phys. Rev. B 76 (2007) 045210] is that it is formulated for arbitrary...

The transport of electrons and light emission under the influene of a lateral electric field in InGaAs/GaAs heterostructures with double tunnel-coupled quantum wells has been studied. For the selectively doped structures at 4.2 K and electric fields ∼1 kV/cm, we have found that the rate of current growth diminishes with increasing field, and simult...

It is shown experimentally that reflection of the acoustic flux from the sample borders under the conditions of formation of a static acoustoelectric domain in a n-InGaAs/GaAs quantum-well heterostructure in a lateral electric field substantially affects the duration of the incubation period of domain formation and the shape and amplitude of curren...

It is shown experimentally that when an acceptor impurity is shifted from the center to the edge of the quantum wells in Si/Si1-xGex heterostructures, the binding energy of the ground state of the impurity decreases and the radius of localization of the carriers increases.

The current oscillations and strong-field domains arising in multilayer n- InGaAs/GaAs heterostructures with δ-doped quantum wells are studied. As shown, in such structures under strong electric fields, an acoustoelectric domain is formed and localized in the near-anode region. The current oscillations show a damping behaviour, and an incubation pe...

An expression for the coefficient of light absorption by "hot" electrons in many-valley semiconductors for carrier scattering by nonpolar optical phonons in dependence on the carrier temperature and electron concentration in each valley has been obtained. It was shown that taking into account the contribution of such scattering into absorption of a...

Infrared light scattering by plasmons in p-Ge has been studied under uniaxial stress along the [110] axis with polarization of incident light parallel to the stress direction. It is found that the deformation of the crystal results in an increase of the plasma frequency and lowering the asymmetry of the line by plasma scattering. These effects are...

The intensity of polarized spontaneous emission as a function of uniaxial stress in p-Ge is studied. It is found that with rising of stress dependence of the radiation polarization rotates by π/2. The effect is explained by the modification of the energy spectrum of free and impurity states under the uniaxial compression.

The pressure-dependent behavior of quasi-local impurity states (QIS) induced by shallow impurity centers in uniaxially stressed p-Ge is described theoretically within screened Coulomb potential model. Dependences of energy position and broadening (lifetime) of QIS on pressure are calculated. They differ fundamentally from the results obtained withi...

Probabilities of intra- and intersubband acoustic scattering of holes in uniaxially stressed p-Ge in electric field are calculated. Perturbation of the free hole states by impurity potential is taken into account. Perturbation has a resonant nature and takes maximum values in the region of hole energy around energy position of quasi-local impurity...

We have studied backward-degenerate four-wave mixing at CO2 laser wavelengths in n-type Ge having a free electron density of N=5×1016cm-3. The phase conjugation due to the redistribution of free electrons between the equivalent valleys was observed. The effect occurs only when the electric field E of the light wave is aligned nonsymmetrically relat...

Inelastic scattering of 10.6 mu m CO2 laser radiation by free carriers has been studied in p-type Ge for a wide range of hole concentrations (5*1015-5*1017 cm-3). Scattering by unscreened single-particle excitations as well as by collective ones was observed. It is found that single-particle scattering arises from fluctuations of the quadrupole mom...

Many - valley cubic semiconductors are optically isotropic crystals in near and medium IR range of spectrum. However, many - valley structure of energy bands gives rise to a number of peculiarities of optical characteristics. In this work it is shown theoretically tuperlattices depends on a light polarization. We also report about experimental obse...

We report the experimental proof of the self-induced birefringence of infrared light in many-valley cubic semiconductors. The effect is connected with the redistribution of free electrons between the equivalent valleys on account of heating by the infrared wave. The agreement of the obtained data with the theoretical prediction is very good.

Measurements of the electron and light emission from discontinuous carbon films excited by passing current or C02-laser irradiation are reported. The most probable mechanism of electron emission from discontinuous films, both on passing current and laser excitation, is the emission of hot electrons from carbon islands. The peaks observed in the rad...

Large heat pulse transfer from film heater into helium at bath temperature 1.7–3 K is considered. Experiments were carried out at vaporization onset and at the film heater temperature in He I and He II. The presence of nonequilibrium layer accounts for no difference in the mechanisms of heating up to the vaporization onset of He I and He II in the...

The propagation of acoustic phonons in GaAs generated by laser radiation of a clean as well as Au coated surface are experimentally investigated in dependence on the crystallographic orientation. The angular dependence of the T1 phonon spectrum is confirmed by comparison with the calculated focussing factor. Besides the ballistic motion of modes of...

A method to measure transient heat transfer to liquid helium from a thin metal film heater under the condition of pulsed heating during τ ≤ 400 ns is proposed. The experimental equipment used for the measurements is described. The method is based on the comparison of heat pulses transfered from the heater into a monocrystal substrate which is surro...