Papers by Keyword: Proton Irradiation

Abstract: In this paper, the effects of various proton irradiation energies and doses on the electrical characteristics of SiC MOSFETs have been evaluated and characterized using a proton accelerator. The devices under test were designed, fabricated and packaged using 1.2 kV/0.6 µm-tech SiC MOSFET processes. The results demonstrate that the threshold voltage (V_th) of the irradiated devices shifted towards negative values due to the radiation-induced positive oxide trapped charges. Moreover, this negative shift in V_th and positive trapped charges of field limiting ring (FLR) oxide led to an increase in output currents and a reduction in the breakdown voltage values.

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: In this work, the impact of 200 MeV proton irradiation at a fluence of 6 × 10¹² cm⁻² on the forward characteristics and the breakdown behaviour of nickel (Ni) and titanium (Ti) Schottky barrier diodes is explored. An improvement in the ideality factor, reduction in the threshold voltage, and an increase in the breakdown voltage is observed post irradiation. Point defects induced by the irradiation are likely responsible for the observed effects. Deep Level transient Spectroscopy (DLTS) measurements were performed on the irradiated Schottky diodes to analyse the defects created during the irradiation and gauge their potential role in changing the diode behavior. The defects induced by the high-energy protons were compared to those formed by low-energy proton irradiation at 1.8 MeV to a fluence of 1 × 10¹² cm⁻². Finally, consecutive DLTS measurements were performed after a series of reverse bias anneals at low temperatures from 350-700 K to explore the annealing behaviour of the defects induced by the proton irradiations.

Abstract: For validating the number of displacements per atom (dpa) for tungsten under high-energy proton irradiation, we measured displacement cross sections related to defect-induced electrical resistivity changes in a tungsten wire sample under irradiation with 389-MeV protons under 10 K. The Gifford–McMahon cryocooler was used to cool the sample using a conductive coolant via thermal conduction plates of oxygen-free high-conductivity copper and electrical insulation sheets of aluminum nitride ceramic. In this experiment, the displacement cross section was 1612 ± 371 b for tungsten at 389 MeV. A comparison of the experimental displacement cross sections of tungsten with the calculated results obtained using Norgett–Robinson–Torrens (NRT) dpa and athermal recombination-corrected (arc) dpa cross sections indicates that arc-dpa was in better agreement with the experimental data than NRT-dpa; this is similar to the displacement cross sections of copper. From the measurements of damage recovery of the accumulated defects in tungsten through isochronal annealing, which is related to the defect concentration of the sample, approximately 20% of the damage was recovered at 60 K. This trend was similar to those observed in other experimental results for reactor neutrons.

Abstract: Impact of 15 MeV proton irradiation on electrical characteristics and low frequency noise has been studied in high-power vertical 4H-SiC MOSFETs of 1.2 kV-class at doses 10¹² £ F £ 10¹⁴ cm^-2. The maximum value of the field-effect mobility µ_FЕ depends weakly on F up to F = 2×10¹³ cm^-2. At F = 4×10¹³ cm^-2, the character of the µ_FЕ(V_g) dependence changes radically. The maximum µ_FЕ decreases approximately threefold. The dose F_cr corresponding to the complete degradation of the device is about 10¹⁴ cm^-2. It can be estimated as F_cr» h_e/n₀, where h_e is the electron removal rate and n₀ is the initial electron concentration in the drift layer. In the entire frequency range of analysis f, gate voltages, and drain-source biases, the frequency dependence of the current spectral noise density S_I(f) follows the law S_I ~ 1/f. From the data of noise spectroscopy, the density of traps in the gate oxide N_tv has been estimated. In non-irradiated structures, N_tv » 5.4×10¹⁸ cm^-3eV^-1. At Ф = 6×10¹³ cm^-2, the N_tv value increases to N_tv » 7.2×10¹⁹cm^-3eV^-1. The non-monotonic behavior of the output current I_d and the level of low frequency noise on dose F has been demonstrated.

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 irradiation embrittlement damage of reactor pressure vessel (RPV) steel is one of its primary failure mechanisms. In this work, neutron, ion and proton irradiation experiments were carried on the same commercial RPV steels with the same irradiation fluence under the same temperature of 292°C. Then the nano-indentation hardness tests were performed on the RPV steel before and after irradiation. The results show that the irradiation hardening effects are observed by means of nano-indentation technique under the above three irradiations, and the hardening features are basically the same. While the max variation and increase rate are obviously different between those irradiations. It is found that the main reason of the above differences are caused by different energies of irradiation energetic particles, resulting in different types and quantities of defects. The conclusions in this paper are helpful to select and compare different irradiation experiments to the research of RPV steels irradiation embrittlement damage.

Abstract: Compact simulation models of two key silicon carbide power components, the Junction Barrier Schottky diode and the power MOSFET, which are taking into account the effect of irradiation by highenergy electrons, were developed. Two 1.7 kV class devices: the 14 A JBS diode C3D10170H and the 5 A SiC power MOSFETs C2M1000170D produced by Wolfspeed were irradiated by 4.5 MeV electrons in the dose range up to 2000 kGy. Electrical characteristics were measured prior to and after irradiation. Radiation defects were studied by deep level transient spectroscopy and the effect of irradiation on device characteristics was established. SPICE models taking into account the irradiation fluence were proposed and calibrated using the parameters extracted from experiment. Simulated characteristics show a very good agreement with reality.

Abstract: The influence of 15 MeV proton irradiation temperatures (room temperature (RT) - 700 ° C) on the processes of defect formation in commercially available 4H-SiC JBS structures has been studied. It has been shown that the carrier removal rate does not depend on the irradiation temperature. At the same time, the irradiation temperature affected on the spectrum of introduced radiation defects. The conclusion about the possible influence of SiC crystal lattice structural defects on the processes of radiation defect formation has been made.