Papers by Keyword: Electron Irradiation

Abstract: In the present work, the kinetics of low-temperature annealing (400 °C) of 4H-SiC JBS diodes irradiated by electrons with an energy of 0.9 MeV and with a dose of 1E16 cm^-2 was studied. The dynamics of changes in I-V, C-V characteristics, as well as DLTS spectra are shown. In the course of the work, a thermal cycling effect was discovered, i.e., effect of multiple rapid cooling to the temperature of liquid nitrogen and heating of the samples. As a result of thermal cycling, the barrier capacity increases and the on-resistance (Rs) decreases. In the DLTS spectrum, a level of - 0.38 eV appears, absent in the as-irradiated diodes.

Abstract: The paper is devoted to developing the theoretical basis of the mathematical modelling and computer simulation intended to analyze and control the electron beam-stimulated effects in ferroelectric materials. In order to simulate the electron beam-induced charging dynamics of ferroelectrics the modification of drift-reaction-diffusion model was proposed. The calculation was based on the numerical solution of the continuity equation and Poisson equation. The parameters of the electron irradiation doze and source function were estimated by 3D Monte-Carlo simulation of electron trajectories in the solid specimen. The computation was associated with typical ferroelectrics (LiNbO₃, LiTaO₃) irradiated by intermediate-energy electron bunches specified for SEM. The contribution roles of drift component as well as diffusion component during dynamic charging process were discussed. The simulation results enable us to predict charge distribution, dynamic of the potential distribution, electric field and electron beam-induced component of polarization at the given experimental parameters. These findings can be used to control polarization switching in ferroelectrics electron beam-irradiated by the SEM techniques.

Abstract: A study of how electron irradiation affects the current-voltage (I-V) and electroluminescence (EL) characteristics of two types of 4H-SiC n⁺p structures with p-base and base doping to ~5∙10¹⁵ cm^-3 is presented. The characteristics were measured prior to irradiation and after each of five stages of irradiation with 0.9 MeV electrons at doses in the range from 1∙10¹⁵ to 1.1∙10¹⁶ cm^-2. The irradiation leads to an increase in the recombination current, decrease in the intensity of the edge EL (hν_max≈3.18 eV), and increase in the intensity of the infra-red (IR) EL (hν_max≈1.35 eV), which starts to predominate. Presumably, this indicates that the nonequilibrium carrier lifetime decreases and the concentration of acceptor type defects grows as a result of the irradiation. The IR EL, attributed to a complex defect containing a silicon vacancy, is of interest for development of single-photon sources of light.

Abstract: The change in the current-voltage characteristics and in N_d-N_a values in the base of 4H-SiC Schottky diodes and JBS diodes under irradiation with 0.9 MeV electrons and 15 MeV protons has been studied. The carrier removal rate for the diodes irradiated with electrons was 0.07-0.15 cm^-1, and that in the case of protons, 50-70 cm^-1. It was shown that the devices under study retain rectifying current-voltage characteristics up to electron doses of ~10¹⁷ cm^-2. It was found that the radiation resistance of the SiC-based devices significantly exceeds that of silicon p-i-n-diodes with similar breakdown voltages. The simultaneous effect of high temperature and proton irradiation on the characteristics of 4H-SiC pn structures was examined.

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 Z_1/2 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.

Abstract: It is well known that intermetallic compound alloys possibly include more than two types of vacancies basically, that is A-vacancy and B-vacancy in A-B compound alloy. Although MeV ordered electron irradiation produces vacancies and interstitials, the threshold energy of displacement for each elemental atom in intermetallic alloys is not necessarily same. Then the defect type introduced by the irradiation depends on electron energy. In this study, we performed positron annihilation lifetime and Doppler broadening measurements for different energy of electron irradiated B2 type Fe50%Al alloy. The values of positron annihilation lifetime for this alloy after 2 and 9 MeV electron irradiation were 200 and 172 psec, respectively. Also, the Doppler broadening parameters S and W show difference for this alloy with different energy of electron irradiation. These results suggest that different types of vacancy were induced into Fe-Al compound alloy by electron irradiation with different energies.

Abstract: Nitride-based light emitting diodes (LEDs) is an attractive material due to its high temperature tolerance and suitable to be used in extreme environment. The irradiation process of Gallium Nitride (GaN) diode was carried out by electron irradiation with 1000 kGy and 1500 kGy doses with a conveyor speed of 50 kGy per pass. Capacitance-voltage (C-V) and current-voltage (I-V) characterization for both pre and post irradiation samples was done. Both current and capacitance show decreasing while reverse leakage current increased after irradiation. The reverse leakage current revealed that the current were start leakage at 1.0 x10 ^-7 A and 1.0 x10^-9 A for 1000 kGy and 1500 kGy irradiations respectively. The current-voltage graph indicated that the effect of electron irradiation on diode produced weak spots as defect cause leakage current. The traps and bulk defect is believed to contributed to the leakage current increased.

Abstract: The effect of low doses of gamma and electron irradiation on mechanical strength of Bi₂Sr₂CaCu₂O₈ (Bi-2212) superconductor ceramics was studied by exposing the superconductor to gamma irradiation dose of up to 50 kGy, and electron irradiation dose of up to 80 kGy. All the samples were prepared using the conventional solid-state reaction method. For samples to be irradiated with electron particles, 5% weight percentage of nanosized MgO was added to absorb certain amount of the energy from electrons and thus reducing the formation of complicated defects structure in the Bi-2212 superconductor. The SEM micrographs of the Bi-2212 superconductor showed the existence of platelet-type grains of Bi-2212 phase in both non-irradiated and irradiated samples. The XRD patterns for the non-irradiated and irradiated samples showed well-defined peaks of which could be indexed on the basis of a Bi-2212 phase structure. The phase purity, lattice parameter, surface morphology and degree of crystallinity for the non-irradiated and irradiated samples were also compared and analyzed and it was found that both the gamma and electron irradiation have considerable effect on the mechanical properties of Bi-2212 superconductor. When subjected to gamma and electron irradiation, the microstructure of the samples was found to be more textured and consequently enhanced the strength of the samples.

Abstract: The article is devoted to the analysis of polarization reversal process arising in ferroelectrics under electron beam exposure. The advanced model was proposed to describe the polarization switching process in ferroelectrics as well as formation of polarization switching response in electron beam-induced polarization current mode of SEM taking into account the specific character of domain structure dynamics. Simulation of polarization switching current in TGS ferroelectric crystals was performed to estimate the main characteristics of electron beam-induced polarization reversal processes.

Abstract: Electrical properties of radiation-produced defects in p-Ge irradiated with MeV electrons and protons are investigated. The dominant defects in electron-irradiated p-Ge were found to be neutral for the most part, whereas they are electrically active in proton-irradiated materials. Evidently, the reactions between impurity atoms and intrinsic point defects leading to formation of secondary Ga-related defects in electron-and proton-irradiated p-Ge appear to be distinct. Production rates of radiation defects in n-Ge and p-Ge are compared. A marked difference in the removal rates of shallow donor/acceptor impurity states, at least by an order-of-magnitude, is thought to be due to greatly enhanced annihilation of Frenkel pairs in p-type Ge.