Showing papers by "Alexander A. Lebedev published in 2018"
TL;DR: In this article, the current voltage characteristics and low-frequency noise in high voltage 4H-SiC junction barrier Schottky diodes irradiated with high energy (15 MeV) protons were studied at different temperatures and irradiation doses.
Abstract: The current voltage characteristics and the low-frequency noise in high voltage 4H-SiC junction barrier Schottky diodes irradiated with high energy (15 MeV) protons were studied at different temperatures and irradiation doses Φ from 3 × 1012 cm−2 to 1 × 1014 cm−2. Irradiation led to the increase of the base resistance and the appearance of slow relaxation processes at small, V ≤ 0.2 V, and at rather high, V ≥ 2 V, forward voltages. The characteristic times of these relaxation processes ranged from ∼1 μs to 103 s. The exponential part of the current-voltage characteristic was only weakly affected by irradiation. The temperature dependence of the base resistance changed exponentially with temperature with activation energy Ea ∼ 0.6 eV, indicating that the Z1/2 level plays a dominant role in this process. The temperature increase also led to the increase of the ideality factor from 1.05 at 25 °C to 1.1 at 172 °C. At elevated temperatures and high forward voltages V > 2–4 V, the current voltage characteristic...
24 citations
01 Dec 2018
TL;DR: In this article, the authors presented the results of an investigation of thin layers of MoSe2 on graphene by Scanning Probe Microscopy (SPM) methods, and the dependence of the surface potential on air humidity was shown.
Abstract: This work presents the results of an investigation of thin layers of MoSe2 on graphene by Scanning Probe Microscopy (SPM) methods. Dependences of the surface potential and work function on the number of monolayers of the structure are presented. The dependence of the surface potential on air humidity is shown. The band structure and doping of the MoSe2 monolayer on graphene was determined. These data can be important for detecting of the number of MoSe2 layers and for designing nanodevices, because the surface potential has a strong influence on the operation of such devices.
10 citations
TL;DR: In this article, the intercalation of iron under a graphene monolayer grown on 4H-SiC(0001) was studied, and it was found that intercalated iron atoms are localized not only between graphene and a buffer layer coating SiC, but also under the buffer layer itself.
Abstract: The intercalation of iron under a graphene monolayer grown on 4H-SiC(0001) is studied. The experiments have been carried out in situ under conditions of ultrahigh vacuum by low-energy electron diffraction, high-energy-resolution photoelectron spectroscopy using synchrotron radiation, and near carbon K-edge X-ray absorption spectroscopy. The deposited iron film thicknesses have been varied within 0.1–2 nm and the sample temperatures from room temperature to 700°C. It is shown that the intercalation process begins at temperatures higher than ~350°C. In this case, it is found that intercalated iron atoms are localized not only between graphene and a buffer layer coating SiC, but also under the buffer layer itself. The optimal conditions of the intercalation are realized in the range 400–500°C, because, at higher temperatures, the system becomes unstable due to the chemical interaction of the intercalated iron with silicon carbide. The inertness of the intercalated films to action of oxygen is demonstrated.
9 citations
TL;DR: In this paper, the structural and electronic characteristics of epitaxial graphene films grown by thermal decomposition of the Si face of a semi-insulating 4H-SiC substrate in an argon environment have been studied by a large set of analytical techniques.
Abstract: The structural and electronic characteristics of epitaxial graphene films grown by thermal decomposition of the Si face of a semi-insulating 4H-SiC substrate in an argon environment have been studied by a large set of analytical techniques. It is shown that the results of a complex study make it possible to optimize the growth parameters and develop a reliable technology for the growth of high-quality single-layer graphene films. The charge-carrier concentration in the graphene layer was within 7 × 1011–1 × 1012 cm–2, and the maximum mobility of electrons at room temperature approached 6000 cm2/(V s).
8 citations
TL;DR: In this paper, the radiation hardness of three types of commercial Schottky rectifier diodes based on silicon carbide (4H-SiC, base layer doping level (3-7) × 1015 cm-3) under electron (0.9 or 3.5 MeV electrons) and proton irradiation (15 MeV protons) is studied.
Abstract: The radiation hardness of three types of commercial Schottky rectifier diodes based on silicon carbide (4H-SiC, base layer doping level (3–7) × 1015 cm–3) under electron (0.9 or 3.5 MeV electrons) and proton irradiation (15 MeV protons) is studied. The forward and reverse current–voltage characteristics of the diodes are monitored. In the initial state, the diodes have a breakdown voltage of 1–2 kV and an almost ideal forward current–voltage characteristic. It is found that the series resistance of the diodes is the most sensitive to radiation and governs the radiation hardness. This resistance grows by nearly 10 orders of magnitude and reaches a value of 109 Ω at high doses. The threshold doses of electron irradiation fall within the range Dth ≈ (0.5–2) × 1016 cm–2 and depend on the electron energy and doping level of the base layer, and those of proton irradiation, Dth ≈ 5 × 1013 cm–2.
7 citations
01 Sep 2018
TL;DR: In this article, the optical and electrical properties of MoSe2 monolayer transferred to graphene/SiC substrate are studied by scanning probe microscopy and photoluminescence spectroscopy.
Abstract: Optical and electrical properties of MoSe2 monolayer transferred to graphene/SiC substrate are studied by scanning probe microscopy and photoluminescence spectroscopy. By Kelvin probe microscopy it was measured a work function of the MoSe2 monolayer (4.3 eV) and it was revealed the n-type of doping. With the increasing of MoSe2 layers quantity the work function also increases which leads to the reducing of the Schottky barrier height between the SPM probe and the layers. Monolayer graphene quenches photoluminescence of the MoSe2 monolayer while the bilayer graphene does not perturb the photoluminescence.
7 citations
TL;DR: In this article, the authors studied electrical transport in transistors fabricated on a surface of high quality epitaxial graphene and observed quasistatic hysteresis with a time constant in a scale of hours.
4 citations
TL;DR: In this article, the electrical properties of GaAs nanowires grown on a 6H-SiC (0001) substrate covered with graphene single layers and bilayers were studied.
Abstract: The electrical properties of GaAs nanowires grown on a 6H-SiC (0001) substrate covered with graphene single layers and bilayers are studied. The nanowires are grown by molecular-beam epitaxy, with gold as a catalyst. The electrical properties are studied by measuring and analyzing the current–voltage characteristics of single nanowires vertically grown on a substrate. Numerical simulation of the experimental current–voltage curves revealed the presence of a ~0.6-V-high Schottky barrier between the nanowires and graphene. The appearance of the barrier is due to the formation of excess arsenic at the nanowire/graphene interface.
3 citations
TL;DR: In this article, the specific features of Frenkel-pair generation upon the scattering of 8- and 15-MeV protons are investigated. And the distribution histograms of energies acquired not only by primary knocked-out atoms, but also by recoil atoms generated in displacement cascades, are calculated.
Abstract: Mathematical simulation of the cascade of displacements in SiC is used to consider the specific features of Frenkel-pair generation upon the scattering of 8- and 15-MeV protons. The distribution histograms of energies acquired not only by primary knocked-out atoms, but also by recoil atoms generated in displacement cascades, are calculated. An analysis of the histograms considers two energy ranges. In the first range of “low” energies, the spontaneous recombination of genetically related Frenkel pairs is dominant. Recoil atoms in the second range have a higher energy, which enables these atoms to leave the spontaneousrecombination zone and dissociate into isolated components. The compensation of lightly doped n- and p-4H-SiC samples grown by gas-phase epitaxy is experimentally studied under irradiation with 8- and 15-MeV protons. The carrier removal rates are measured. The calculated and experimental data are compared and estimates are obtained for the size of the spontaneous-recombination zone.
2 citations
TL;DR: In this paper, the MBE growth of GaP and InP nanowires on a SiC substrate with a graphene layer is demonstrated for the first time, and the results of structural measurements demonstrate that the nanowsires are formed in the wurtzite phase, which is not typical of bulk III-V materials.
Abstract: The possibility in principle of the MBE (molecular-beam epitaxy) growth of GaP and InP nanowires on a SiC substrate with a graphene layer is demonstrated for the first time. InP nanowires on such a substrate have no stacking faults and possess an ideal crystallographic quality. At the same time, GaP nanowires have structural defects of the type of twins and the reversal of crystallographic phases at the top and at the base. The results of structural measurements demonstrate that the nanowires are formed in the wurtzite phase, which is not typical of bulk III–V materials.
2 citations
TL;DR: In this article, it was shown that the transport properties of graphitized silicon carbide are controlled by a surface graphene layer heavily doped with electrons, and a crossover in the magnetoresistance from weak localization to weak antilocalization was observed for the first time in samples of this kind at elevated temperatures.
Abstract: It is shown that the transport properties of graphitized silicon carbide are controlled by a surface graphene layer heavily doped with electrons. In weak magnetic fields and at low temperatures, a negative magnetoresistance is observed due to weak localization. A crossover in the magnetoresistance from weak localization to weak antilocalization (the latter is the manifestation of the isospin in graphene) is observed for the first time in samples of this kind at elevated temperatures. A pronounced pattern of Shubnikov–de Haas oscillations is observed in strong magnetic fields (up to 30 T). This pattern demonstrated fourfold carrier spectrum degeneracy due to the double spin and double valley degeneracies. Also, the manifestation of the Berry phase is observed. The effective electron mass is estimated to be m* = 0.08m0, which is characteristic of graphene with a high carrier concentration.
TL;DR: In this paper, the electrical properties of monolayer graphene, prepared by thermal decomposition of silicon carbide in argon, in the field effect transistor and the four-probe geometries are investigated.
Abstract: Establishing the features of interfacial effects on the electrical conductivity of graphene is crucial for successful design of novel graphene-based electronic devices, including chemical sensors and biosensors. We study electrical properties of monolayer graphene, prepared by thermal decomposition of silicon carbide in argon, in the field-effect transistor and the four-probe geometries. Alterations in the electrical properties of graphene in response to placing a quantity of water on its surface followed by removal of the water are investigated. In these geometries, the field effect is shown to play a key role in the way the electrical properties of graphene are affected by the formation of the graphene–water interface.
19 Dec 2018
TL;DR: In this article, reflection high-energy electron diffraction (RHEED) is used for studying the structure of graphene layers formed on the surface of the Si-face of conductive and semi-insulating 6H- and 4H-SiC(0001) substrates by thermal desorption of Si atoms in high vacuum, depending on the temperature and time of sublimating Si atoms as well as depending on a method of preprocessing the substrate surface.
Abstract: The method of reflection high-energy electron diffraction (RHEED) is used for studying the structure of graphene layers formed on the surface of the Si-face of conductive and semi-insulating 6H- and 4H-SiC(0001) substrates by thermal desorption of Si atoms in high vacuum, depending on the temperature and time of sublimating Si atoms as well as depending on the method of preprocessing the substrate surface. Diffraction patterns are recorded in the $$[\bar 12\bar 10]$$
and $$[1\bar 100]$$
crystallographic directions of the substrates. It is found that in all experiments the formation of graphene layers occurs with a rotation of the graphene crystal lattice by 30° relative to the SiC lattice.
TL;DR: In this article, it was shown that the high voltage Ni/4H-SiC Schottky diodes with the dose Φ=(0.2-7)×1016cm-2 led to an increase in the base resistance, appearance of slow relaxation processes at extremely small currents, and increase of low frequency noise.
Abstract: Electron irradiation of high voltage Ni/4H-SiC Schottky diodes with the dose Φ=(0.2-7)×1016cm-2 led to increase in the base resistance, appearance of slow relaxation processes at extremely small currents, and increase of the low frequency noise. On exponential part of the current-voltage characteristics and on linear part of current-voltage characteristics in non-irradiated samples, low frequency noise always has the form of the 1/f noise. On linear part of the current-voltage characteristics in irradiated diodes the generation recombination (GR) noise predominates. Temperature dependences of the base resistivity and character of GR noise indicate that mainly Z1/2 center contributes to the change in the parameters of irradiated samples. Capture cross section of this level, obtained from noise measurements, is within the range (8×10-16-2×10-15) cm2 and only weakly depends on temperature.
TL;DR: In this article, the authors studied JBS diodes based on 4H-SiC irradiated with electrons and protons and concluded that deep centers are formed in the upper half of the band gap of silicon carbide.
Abstract: JBS diodes based on 4H-SiC irradiated with electrons and protons are studied. This is carried out by using the methods of capacitance–voltage and current–voltage characteristics. It is concluded that, for both kinds of irradiation, deep centers are formed in the upper half of the band gap of silicon carbide. This leads to a sharp decrease in the concentration of ionized carriers in the conduction band and to an exponential increase in the resistance of the base regions of the structures under study.