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[en] Issues related to the production of radiation defects in silicon carbide of various polytypes and with differing conductivity types and concentrations of charge carriers as a result of irradiation with high-energy particles in a wide range of their energies and masses (from electrons to heavy Bi ions) are considered. The effect of irradiation with high-energy particles on the optical and electrical characteristics of the devices based on SiC are also considered, including the devices that operate as detectors of nuclear radiation. Systematic trends (common to other semiconductors and characteristic of SiC) in the radiation-defect formation in SiC are established. The high radiation resistance of SiC is verified; it is shown that this radiation resistance can be increased at increased energies of incident particles and at higher temperatures of operation
[en] The current management system in the United States for commercial spent nuclear fuel does not emphasize integration among storage, transportation, and disposal. The large containers in use for dry-storage remain at high temperatures for decades and, thereby, delay removal from decommissioned reactors. The large containers also have no easy path to disposal unless (1) disposal is delayed (up to 150 years for some geologic media); (2) the contents are repackaged into smaller, cooler packages; or (3) the high temperatures are used as de facto site-selection criteria for a repository. Implementing consolidated interim storage could address many issues that exist because of this lack of integration. A consolidated interim storage facility that includes appropriate capabilities acts as a universal coupler that allows existing disparate parts to integrate as a system. Previous agencies and commissions have noted this theme before as a way to provide flexibility in the waste management system. This rationale is elaborated upon here. (author)
[en] Al ion implantation of chemical-vapor deposition (CVD)-grown n-type films has been used to fabricate p+–n junctions for nuclear particle detectors. The junction formation mode is characterized by a high dose of Al ions and a short-duration (15 s) activating annealing. Specific structural features of the implanted p+–n junctions, revealed using modern analytical techniques, are accounted for by the joint action of the high-dose Al ion implantation and unconventional rapid thermal annealing mode. The detector characteristics were studied up to a temperature of 375 °C under irradiation with 3–8 MeV alpha particles in a vacuum chamber of special design. An improvement of the energy resolution and nonequilibrium charge collection efficiency was observed with increasing temperature. The results obtained are explained in terms of specific structural features of the p+–n junctions formed in the chosen implantation and thermal annealing modes. The behavior of the detector noise level was analyzed with the working temperature raised up to 375 °C
[en] A method for studying the Earth’s ionosphere at altitudes of the mesosphere and lower thermosphere based on creating artificial periodic irregularities in the ionospheric plasma by means of powerful radio waves is breafly described. Methods for determining the temperature and density of the neutral component and the velocity of vertical and turbulent motions by measuring the characteristics of the signal backscattered by the irregularities are described. The results of experiments performed on a SURA heating facility aimed at a comprehensive investigation of the natural processes occurring in the Earth’s lower ionosphere due to the propagation of atmospheric waves and turbulent phenomena are examined. Based on measurements of the amplitude and phase of the signal scattered by periodic irregularities, the most important characteristics of the neutral and plasma components of the Earth’s atmosphere at altitudes of the mesosphere and lower thermosphere are determined. Further research on the subject is discussed.
[en] The problems of the radiation resistance of diodes for different purposes, created on the basis of lightly doped epitaxial n-4H-SiC layers with Schottky barriers and ion-doped p‒n- and n‒p junctions, are considered. The effect of irradiation with high-energy particles in a wide range of energies and masses—from electrons to Bi heavy ions—on the electrical and optical characteristics of 4H-SiC-based devices is studied. The general regularities of radiation-defect formation under irradiation with different high-energy particles are shown. The high radiation resistance of 4H-SiC is confirmed, and the possibility of increasing its radiation durability and endurance with high energies of irradiating particles and at operating temperatures of up to 400–500°C is shown.
[en] For the first time, comprehensive comparative investigations of ultraviolet photodetectors with Cr Schottky barriers formed on 4H-SiC epitaxial layers are carried out by the X-ray and optical methods before and after irradiation with 15-MeV protons with fluences in the range of (1–4) × 1012 cm–2. When increasing the fluence of proton irradiation, the formation of localized regions with negative deformation is observed along with the unperturbed silicon-carbide matrix. Agreement between the X-ray and optical studies is obtained, which makes it possible to explain the features of the spectral changes in the photosensitivity of detectors in the range of 200–400 nm with an increase in the fluence of proton irradiation. The ultraviolet Cr/4H-SiC photodetectors withstand irradiation by 15-MeV protons with a fluence of 4 × 1012 cm–2 virtually without any changes in the photosensitivity due to the gettering of simple defects by cluster and amorphous formations, which lead to partial structural improvement of the irradiated material.
[en] Results obtained in a study of spectrometric characteristics of arrays of four detectors based on 4H-SiC ion-implantation-doped p+-n junctions in the temperature range 25-140 deg. C are reported for the first time. The junctions were fabricated by ion implantation of aluminum into epitaxial 4H-SiC layers of thickness ≤45 μm, grown by chemical vapor deposition with uncompensated donor concentration Nd - Na = (4-6) x 1014 cm-3. The structural features of the ion-implantation-doped p+-layers were studied by secondary-ion mass spectrometry, transmission electron microscopy, and Rutherford backscattering spectroscopy in the channeling mode. Parameters of the diode arrays were determined by testing in air with natural-decay alpha particles with an energy of 3.76 MeV. The previously obtained data for similar single detectors were experimentally confirmed: the basic characteristics of the detector arrays, the charge collection efficiency and energy resolution, are improved as the working temperature increases
[en] Results obtained in a study of spectrometric characteristics of arrays of four detectors based on 4H-SiC ion-implantation-doped p+-n junctions in the temperature range 25–140 °C are reported for the first time. The junctions were fabricated by ion implantation of aluminum into epitaxial 4H-SiC layers of thickness ≤45 μm, grown by chemical vapor deposition with uncompensated donor concentration Nd − Na = (4–6) × 1014 cm−3. The structural features of the ion-implantation-doped p+-layers were studied by secondary-ion mass spectrometry, transmission electron microscopy, and Rutherford backscattering spectroscopy in the channeling mode. Parameters of the diode arrays were determined by testing in air with natural-decay alpha particles with an energy of 3.76 MeV. The previously obtained data for similar single detectors were experimentally confirmed: the basic characteristics of the detector arrays, the charge collection efficiency and energy resolution, are improved as the working temperature increases.
[en] The radiation-induced defect formation in high purity 4H-SiC CVD epitaxial layers and changes in the electrical properties of diode structures based on its after irradiation with different fluences 1 MeV neutrons were investigated at temperatures as high as 700 K. The Z1 deep center, typical for 4H-SiC, was observed both in the initial and irradiated samples. The presence and number of different deep levels increased with the neutron fluence. The rectifying properties of the diode structures disappeared after neutron irradiation with fluence of 6.2 x 1014 cm-2. However, the diode structures that had been degraded after irradiation with fast neutrons, recovered their properties at the temperature of 700 K. (orig.)
[en] A combination of a high-dose (5 s- 1016 cm-2) implantation of Al ions into epitaxial n-type 4H SiC layers grown by chemical deposition from th e vapor phase and rapid (15 s) thermal annealing at 1700-1750 deg. C has been used to form layers with a rectangular impurity profile according to the mechanism of solid-phase epitaxial crystallization. The combined effects of enhanced diffusion of radiation defects after implantation and gettering of defects during annealing bring about an improvement in the quality of the initial material, which ensures an increase in the diffusion length of the minority charge carriers by several times. Metastable states annealed within different temperature ranges are formed in SiC under the effect of irradiation with various particles. Low-temperature annealing of radiation defects increases the radiation and temporal lifetime of devices under irradiation. High-temperature annealing of radiation defects makes it possible to vary the lifetime of nonequilibrium charge carriers, i.e, vary the frequency range of devices. The radiation resistance of SiC-based devices increases as the operation temperature is increased to 500 deg. C.