Papers by Keyword: Electron Irradiation

Abstract: The effect of high-temperature electron and proton irradiation on SiC-based device characteristics is being investigated. Industrial integrated 4H-SiC Schottky diodes, each with an n-type base and a blocking voltage of either 600 V, 1200 V, or 1700 V, manufactured by Wolfspeed, are being studied. 0.9 MeV electron and 15 MeV proton irradiation were applied. It has been found that the irradiation resistance of silicon carbide Schottky diodes at high temperatures significantly exceeds their resistance at room temperature. This effect is attributed to the annealing of compensating defects induced by high-temperature irradiation. The parameters of radiation-induced defects are determined using the method of deep level transient spectroscopy (DLTS). Under high-temperature ("hot") irradiation, the spectrum of radiation-induced defects introduced into SiC appears to differ significantly from the spectrum of defects introduced at room temperature. It is suggested that approximately half of the compensation is due to radiation-induced defects formed in the bottom part of the bandgap.

Abstract: The paper is devoted to the study of the influence of factors on the rate of return deformation of polytetrafluoroethylene. The dependence of the rate of return strain (ε'_r) on time (t), the dose of electron irradiation (D) and mechanical stress (σ) in thin films of polytetrafluoroethylene has been experimentally investigated. Significant variations of ε'_r have been found dependingon on t, D and σ. A decrease in the rate of return deformation during irradiation of the material is associated with the frictional properties between macromolecules and a change in the structure, which leads to a weaker straightening of the polymer and their poor sliding. The resulting curves for both unirradiated and irradiated material are satisfactorily described in the exponential and linear models. For dependencies ε'_r on D, these are decreasing functions, and for ε'_r on σ, these are increasing functions.

Abstract: The study of the deformation characteristics of thin polymer films has established 2 stages of increasing strain with increasing stress: the first stage in the elastic region is slow linear; the second stage is sharply exponential. The dependence of deformation (ε) on stress (σ) in polytetrafluoroethylene at various exposure doses has been experimentally investigated. Irradiation of the fluoroplastic films under study with electrons doses of 1, 3, 5, 7, and 10 kGy leads to significant changes in their mechanical properties, while the samples lose their plasticity and begin to break at a lower strain, which is associated with the formation of nanodefects in the structure of the material. A significant decrease in elongation is observed compared with unirradiated material. The reason for this is the degradation of the main chains of the fluoroplastic. With an increase in the absorbed dose, the Young's modulus increases exponentially, which is associated with a decrease in the distance between atoms in the structure of the sample. The resulting effect can be used in industry. The curves obtained for both non-irradiated and irradiated material are satisfactorily described in the exponential model.

Abstract: The change in the positron annihilation lifetime (PAL) of vacancy clusters before and after electrolysis hydrogen charging was determined using PAL measurements in electron-irradiated F82H. The experimental change indicated 8 hydrogen atoms were trapped in vacancy clusters; whereas the theoretical calculation resulted in approximately 14 atoms. As the samples were left at room temperature for 5 min until the start of the PAL measurements, the de-trapping effect of hydrogen atoms was also considered; approximately 13 hydrogen atoms were captured at each vacancy cluster. The PAL decreased after annealing at 148 K, which could not be explained theoretically. Therefore, further experiments and discussions are needed to obtain a precise change in the PAL of vacancy clusters containing hydrogen atoms in F82H.

Abstract: Herein, we compared thermal desorption analysis (TDA) curves obtained by conducting experiments and simulations. In addition, we discussed the validation of our simulations and trapping sites of hydrogen atoms. In as-received F82H, when the samples contained solute atoms, grain boundaries, dislocations, and precipitates, the experimental curve corresponded to the simulated curve. In positron annihilation lifetime (PAL) measurements, di-vacancies were detected in the electron-irradiated F82H. When we changed the growth and the concentration of vacancy-type defects during temperature increase using the rate theory, the simulation results agreed with experiment results. In creep-ruptured Fe, only dislocations were detected by the PAL measurements. However, the existence of a type of defect, which was related to grain boundaries, must be assumed to fit the simulation curve to the experimental one. In the next step, the diffusion of hydrogen atoms on grain boundaries should be added to simulation program.

Abstract: In this paper, the detail study of electrical conductivity of single layer graphene (SLG) on silicon dioxide (SiO₂)/Silicon substrate irradiated by high energy (MeV) electron is presented. The SLG samples prepared by Chemical Vapor Deposition (CVD) were irradiated by 50 kGy, 100 kGy and 200 kGy doses of electron radiation at energy voltage of 3 MeV. Current-Voltage (I-V) characteristics and conductivity of the pristine and irradiated graphene samples were measured and analysed using I-V measurement at room temperature. The non-linear I-V curves were clearly observed as the voltage reach to 2.0 V for non-irradiated and irradiated samples. This may be attributed to the non-uniform charges by high energy electron irradiation and poor metal contact of the sample. Hysteresis loop form at 2.0 V probably due to the to the charge trapping occurs at the interface of the graphene and SiO_2. The reaction of high energy particles lead to creation of more carrier charges that contribute to the increment of conductivity compare to the small number of atom displacement of knock-on collisions with the nuclei of carbon atoms at higher dose. This study provides significant findings on the graphene electrical characteristics when irradiated with high energy (MeV) electron.

Abstract: SiC has currently attracted the interest of the scientific community for qubit applications. Despite the importance given to the properties of color centers in high-purity semi-insulating SiC, little is known on the electronic properties of defects in this material. In our study, we investigated the presence of electrically active levels in vanadium-doped substrates. Current mode deep level transient spectroscopy, carried out in the dark and under illumination, together with 1-D simulations showed the presence of two electrically active levels, one associated to a majority carrier trap and the other one to a minority carrier trap. The nature of the detected defects has been discussed in the light of the characterization performed on low-energy electron irradiated substrates and previous results found in the literature.

Abstract: Forward and reverse current-voltage (I-V) characteristics of commercial rectifying Schottky diodes (SDs) based on silicon carbide (4H-SiC, base layer doping level 3·10¹⁵ cm^-3) have been studied under irradiation with 0.9 MeV electrons and 15 MeV protons. The starting diodes were characterized by a barrier height of ~1.5 eV and nearly ideal forward and reverse I-V characteristics. It was found that, at doses exceeding the threshold dose D_th, the series differential resistance R_s of the diodes grows as R_s ~ D^m (m = 10-15) and shows no tendency toward saturation. D_th ≈7·10¹⁵ cm^-2 under electron irradiation, and D_th ≈ 4·10¹³ cm^-2 in the case of irradiation with protons. Heating to 200oC results in that R_s decreases with activation energy of ~1.1 eV and R_s is partly annealed-out with activation energy of ~0.7 eV. The starting Schottky diodes changes only slightly under irradiation, but, possibly, the irradiation leads to an over-compensation of the n-type layer and formation of an additional barrier in the form of a pn junction.

Abstract: The influence of low-temperature (up to 400°С) annealing on the current-voltage and capacitance–voltage characteristics of Schottky diodes irradiated with protons with an energy of 15 MeV compared with the results of annealing of structures after irradiation with electrons with an energy of 0.9 MeV has been studied. It was shown that in case of proton irradiation with a dose of 4E13 cm^-2 and electron irradiation with a dose of 1E16 cm^-2, only partial carrier compensation occurs and the differential resistance is completely determined by the number of carriers in the epitaxial layer. The irradiation method has almost no effect on the direct current dependence on the voltage in the exponential segment. The ideality coefficient remains almost unchanged within 1.03 ÷ 1.04. During annealing after proton irradiation, a large activation energy of the process is required. The temperature of the beginning of annealing process during proton irradiation shifts to a larger value, from 150 °C to 250 °C when compared with electron irradiation. It has been demonstrated that at low doses of proton irradiation, the low-temperature annealing leads to the return to the conduction band of up to 65% of the removed charge carriers. After electron irradiation, low-temperature annealing returns up to 90% of the removed charge carriers to the conduction band. This indicates that at room temperature both proton irradiation as well as electron irradiation introduce both stable and unstable defects but in different proportions.

Abstract: The dependence of strain on temperature in polyethylene under various static loads and exposure doses has been studied experimentally. After electron irradiation with doses of 10, 30, 50, 70, and 100 kGy, significant changes in the mechanical properties were observed, which are caused by the formation of nanodefects in the material’s structure. With increasing radiation dose, PE deformation at different temperatures decreases due to destruction in the structure of the polymer material. At the same time, the return deformation increases with increasing dose, indicating a change in the modulus of elasticity (E). The increase in E occurs due to the decrease in the distance between macromolecules in the irradiated structure of the sample. The obtained curves for both non-irradiated and irradiated material are described in an exponential model satisfactorily.