Papers by Keyword: Radiation Defect

Abstract: Non-uniformities of electrical properties of 4H-SiC CVD films have been revealed using physico-chemical reactions occurring upon introduction of radiation-induced structural defects. Primary knocked-out atoms and vacancies actively interact with defects of the starting material and thereby form the final system of radiation centers. The samples were irradiated with 900 keV electrons and 8 MeV protons at doses not leading to conductivity compensation ( 7.5  1012 cm–2) and a dose of 6  1014 cm–2 causing deep compensation. Capacitance methods demonstrated that characteristics of samples ~3 mm in size are not identical. The nuclear spectrometry technique, which enables microprobing of samples, demonstrated individual behavior of separate parts of a film with areas of tens of square micrometers (the dimension of α-particles track cross-section).

Abstract: The objective of this work is to evaluate the microstructure of the neutron-irradiated reduced activation ferritic/martensitic (RAFM) steel EUROFER 97. For this purpose irradiation induced defects like defect clusters, dislocation loops, voids/bubbles and precipitates are identified by transmission electron microscopy (TEM) and quantified in size and volume density. Emphasis is put on analyzing the influence of the irradiation dose and neutron fluxe on the evolution of size and density of the defects at irradiation temperatures between 300 and 335 °C. A first sample irradiated to a dose of 31.8 dpa was analyzed. The irradiation was carried out in the BOR 60 fast reactor of JSC “SSC RIAR” in Dimitrovgrad, within the framework of the ARBOR-1 irradiation program. To study the dose dependence in a next step the results will be compared to quantitative data on samples irradiated to a dose of 15 dpa. The obtained quantitative data will be used for correlation of the changes in the microstructure to the changes in the mechanical properties and will serve as an input for models describing this correlation.

Abstract: The electron momentum distribution and microstructure of centers incorporating a vacancy (vacancies) and a group-V-impurity atom (P, As, Sb, or Bi) in oxygen-lean n-Ge crystals have been investigated by means of the angular correlation of the annihilation radiation (ACAR). The vacancy-group-V-impurity atom complexes have been induced by irradiation with 60Co γ – rays at Tirr. ≈ 280K. A split between the intensities of the high-momentum emission of the annihilation radiation measured before and after n-p-conversion has been revealed for the complexes containing smaller ion cores (P, As) and the larger ones (Sb, Bi), respectively. After n-p-conversion the electron density decreases slightly (but markedly) around the positron localized at the vacancy complexes incorporating P, Sb, and Bi impurity atom. This decrease is accompanied by a lessening of intensity of the high-momentum emission of the annihilation radiation thus bringing in a direct evidence of a multi-vacancy structure of the vacancy-group-V-impurity atom complexes after n-p-conversion; the electron density was found to be affected by the localized deep acceptor states related to these centers. The relaxation inward open volume is a common feature which is pronounced for As-containing complexes. Subvalent band states are suggested to contribute the high-momentum annihilation most markedly. The electron momentum density around the positron is due to rather by the elemental specificity of the surrounding atoms than by changes of the electron-positron many-body interaction in the vacancy-group-V-impurity atom complexes.

Abstract: Defects distribution in 6H-SiC implanted with Bi ions was investigated with the local cathodoluminescence. There are two typical areas with radiation defects found in implanted samples. Implanted layer was about 27 micrometers depth. Far-action area with radiation defects was observed for the first time. Thickness of this area varies from few tens up to hundreds micrometers. This effect depended on concentration of defects i.e. irradiation fluence. Radiation defects at this area disappeared after annealing the sample if fluence is not to high.

Abstract: The influence of platinum contamination on the stability of radiation defects produced by high-energy proton irradiation was investigated in the low-doped n-type float-zone oxygen rich silicon forming the base of power p+nn+ diodes. Platinum was first implanted and then in-diffused at different temperatures to obtain different levels of contamination. Diodes were then implanted with 1.8 MeV protons to a fluence of 2x1010 cm-2 and radiation defect reaction during isochronal annealing were investigated by deep-level transient spectroscopy. Results show that contamination of silicon by platinum atoms influences significantly both the introduction rates and the temperature stability of dominant radiation defects (vacancy-oxygen pairs, divacancies and VOH complexes).

Abstract: The effect of high-energy hydrogen and helium implantation and subsequent annealing on generation of radiation defects and shallow donors in the low-doped oxygen-rich FZ n-type silicon was investigated. Samples were implanted with 7 MeV 4He2+ or 1.8 MeV 1H+ to fluences ranging from 1x109 to 3x1011 cm-2 and 1.4x1010 to 5x1012cm-2, resp., and then isochronally annealed for 30 minutes in the temperature range up to 550°C. Results show that radiation damage produced by helium ions remarkably enhances formation of thermal donors (TDs) when annealing temperature exceeds 375°C, i.e. when the majority of vacancy-related recombination centers anneals out. The excess concentration of TDs is proportional to the helium fluence and peaks at 1.6x1014cm-3 if annealing temperature reaches 475°C. Proton irradiation itself introduces hydrogen donors (HDs) which form a Gaussian peak at the proton end-of-range. Formation and annealing of shallow and deep hydrogen-related levels are strongly influenced by electric field at annealing temperatures below 175°C. If annealing temperature exceeds 350°C, HDs disappear and the excessive shallow doping is caused, as in the case of helium irradiation, by radiation enhanced TDs.

Abstract: The influence of preliminary treatment in hydrogen plasma on elimination of radiation defects and formation of thermal donors has been studied in detector structures made of standard and oxygenated float zone silicon has been studied. A new type of thermal donors has been found in as-treated diodes. These thermal donors are unstable and can be eliminated by heat-treatment at 200-250°C. After irradiation with 3.5 MeV electrons the detectors had been annealed at temperatures of 50-350 °C. It has been found that preliminary hydrogenation at 300 °C leads to disappearance of main vacancy-type radiation defects at lower annealing temperatures. The annealing of hydrogenated and irradiated crystals is accompanied by hydrogen redistribution and formation of hydrogen-related donors. Preliminary irradiation influences on both these processes.

Abstract: The radiation defects in 10 Ω⋅cm p-type and 4.5 Ω⋅cm n-type Cz Si were created at depth of 0.8-1 µm using 100 keV 2⋅1016 at/cm2 hydrogen implantation at room temperature. Then the introduction of nitrogen into silicon and its diffusion were carried out at different thermodynamic conditions. Finally, the samples were vacuum annealed at 800 oС during 2 h. The state of sample surfaces was studied by SEM. The depth and thickness of SixNy layer and also defect numbers were estimated by RBS method in the channeling mode. The electrical properties of the obtained structures were characterized by the transversal conductance measurements with the keep of a standard LCR-meter at a frequency of 1 MHz using the two-probe method. Our experiments have shown that the above-described method enables one to form the buried SiхNy layer with dielectric properties and the number of defects and nitrogen atoms on the silicon surface and in the near-surface region are comparable with those for the initial silicon wafers.

Abstract: 500 keV nitrogen implantations at different tilt angles (0o, 0.5o, 1.2o, 1.6o, 4o) with respect to the c-axis of 6H-SiC were carried out. Radiation damage distributions have been investigated by Backscattering Spectrometry combined with channeling technique (BS/C) using 3550 keV 4He+ ion beam. A comparative simultaneous evaluation of the damage depth distributions in the Si and C sublattices of 6H-SiC led to a correction factor of 0.8 in the electronic stopping power of 4He+ ions along <0001> channel. Full-cascade Crystal-TRIM simulations with the same set of damage accumulation model parameters could reconstruct the measured shapes and heights of damage distributions for all implantation tilt angles. Secondary defect generation effects in addition to the primary point defect accumulation were assumed in the analysis.