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This paper presents thermal expansion coefficient (TEC) and amorphization in 4H-SiC containing point defects at different concentrations. We considered vacancy defects, interstitial defects, and Frenkel pair defects and investigated the thermomechanical response of the lattice over a wide range of temperatures using classical molecular dynamics simulations. The results show that 4H-SiC with vacancy defects exhibits a negative TEC above a critical defect density of around 9% (irrespective of the temperature). With interstitial defects, it exhibits a positive TEC (regardless of the defect density), and with Frenkel pair defects it shows a transition from positive TEC to negative TEC for a defect density greater than 8%. The coupling between temperature-induced expansion and defect-introduced stress in the lattice forms the mechanistic basis for the observed variation in TEC. Furthermore, the specific heat decreases rapidly with an increase in defect density at room temperature, with the highest sensitivity of the lattice observed for the Frenkel pair defects followed by interstitial defects and then by vacancy defects. These findings highlight the critical implications of defects on thermal expansion behavior of 4H-SiC with applications in radiation environments. [ABSTRACT FROM AUTHOR]

Surface damage and fuel retention are one of the major threats to the performance of plasma-facing materials (PFMs) in ITER and future fusion reactors. This work aims to investigate the influence of suppressed blistering by heavy ion pre-damage on deuterium (D) retention in tungsten (W). Recrystallized W samples were irradiated with 3.5 MeV iron (Fe13+) ions at room temperature to create displacement damage with a peak damage level of 0.1 dpa. Afterwards, a series of low-energy (38 eV) D plasma exposures were performed at 500 K. Three exposure fluences below and above the blistering threshold (5 × 1024 ∼ 3 × 1025 D m−2) of the pre-damaged W are selected to decouple and couple the damage-induced defects and blistering-induced defects, respectively. Surface observations show that no blisters are formed in un-damaged W after low-fluence D exposure (5 × 1024 D m−2), whereas severe blistering (surface coverage ratio: 34.2 %) occurs in the high-fluence case (3 × 1025 D m−2). In contrast, only a small number of blisters (4.2 %) are formed in Fe-damaged W when D fluence reaches 3 × 1025 D m−2. Moreover, Fe pre-damage increases D retention by a factor of 3.33 and 1.20 at the low-fluence (5 × 1024 D m−2) and medium-fluence (1 × 1025 D m−2) D exposure, respectively. While in the high-fluence case (3 × 1025 D m−2), the enhancement effect of D retention in Fe-damaged W is significantly weakened, such that retention is lower for damaged W, probably due to the significant suppression effect on surface blistering and its accompanying defect formation. This work highlights the suppressed blistering-induced D retention by pre-existing damage in W.

The synergistic effects on the 0.18 µm PPD CISs induced by neutron displacement damage and gamma ionization damage are investigated. The typical characterizations of the CISs induced by the neutron displacement damage and gamma ionization damage are presented separately. The CISs are irradiated by reactor neutron beams up to 1 × 1011 n/cm2 (1 MeV neutron equivalent fluence) and 60Co γ-rays up to the total ionizing dose level of 200 krad(Si) with different sequential order. The experimental results show that the mean dark signal increase in the CISs induced by reactor neutron radiation has not been influenced by previous 60Co γ-ray radiation. However, the mean dark signal increase in the CISs induced by 60Co γ-ray radiation has been remarkably influenced by previous reactor neutron radiation. The synergistic effects on the PPD CISs are discussed by combining the experimental results and the TCAD simulation results of radiation damage. [ABSTRACT FROM AUTHOR]

AlGaN/GaN high electron mobility transistors (HEMTs) have excellent physical and chemical stability, which gives it great potential for use in consumer, industrial and space applications. However, the defects of epitaxial growth AlGaN/GaN HEMTs are difficult to completely remove, and high-density defects strongly affect the radiation resistance of the devices. Therefore, understanding the evolution and mechanism of defects under particle irradiation is of great significance for improving the radiation resistance. The degradation mechanisms in AlGaN/GaN HEMTs irradiated by 3 MeV protons and 14 MeV neutrons were investigated. After 3 MeV proton irradiations with a flux of 4×1014 cm-2 and 1×1015 cm-2 and 14 MeV neutron irradiations with a flux of 1.2×1012 cm-2 and 2×1013 cm-2, the AlGaN/GaN HEMTs shows decrease in saturation drain current and peak transconductance, positive drift in threshold voltage. The defects of AlGaN/GaN HEMTs induced by irradiation were tested and studied by deep level transient spectroscopy (DLTS). The decreasing of defect concentration induced by 3 MeV proton irradiation reduces the reverse gate leakage current, while 14 MeV neutron irradiation causes defect concentration increases, increasing the reverse gate leakage current. According to the defect energy levels after proton and neutron irradiation are both (0.850±0.020) eV, it is inferred that the defect types are nitrogen interstitial defects. The displacement damage effect caused by the displacement of nitrogen interstitial defects after neutron and proton irradiation is the main reason for the electrical performance degradation of AlGaN/GaN HEMT devices.

GaInP/GaAs/Ge triple junction solar cells have the advantages of high reliability, long life, and high photoelectric conversion efficiency, making them the core components of current spacecraft space power systems. However, the radiation particles in the space environment interact with solar cells and cause displacement damage, leading to the electrical parameters of the solar cells to attenuate, and even causing the failure of spacecraft power supply system, seriously affecting the mission of spacecraft in space. In order to achieve the degradation of the GaInP/GaAs/Ge triple junction solar cells induced by high energy protons, the domestic GaInP/GaAs/Ge triple junction solar cells were taken as the research object, and the radiation experiments of 100 MeV protons under different fluencies were carried out. The experimental results and damage mechanisms of sensitive parameter degradation induced by proton displacement damage in triple junction solar cells, such as open circuit voltage (Voc), short circuit current (Isc), maximum output power (Pm), and photoelectric conversion efficiency (Eff), were analyzed. In order to better analyze the damage caused by 100 MeV protons to the GaInP/GaAs/Ge triple junction solar cells, the transport process of protons was simulated by Geant4 software. The information of the primary knocked-on atoms (PKAs) was obtained by judging the interaction between particles and materials in the transport process. By analyzing the distribution of PKAs in the depth of the GaInP/GaAs/Ge triple junction solar cells caused by 100 MeV protons, it is found that 100 MeV protons can cause uniform displacement damage throughout the entire triple junction solar cell. The above electrical parameters of GaInP/GaAs/Ge triple junction solar cells were tested and analyzed before and after proton irradiation under AM0 and 25 ℃ conditions. The experimental results show that the degradation degrees of normalized Voc, Isc, Pm, and Eff increase with the increase of proton fluence when the fluence range is 1×1011-2×1012 cm-2. When the proton fluence is 2×1012 cm-2, the degradation degrees of normalized Voc, Isc, Pm, and Eff are 8.94%, 3.34%, 16.88%, and 16.88%, respectively. By fitting the degradation degrees of normalized Voc, Isc, and Pm obtained by irradiation with different proton fluences, the characteristic curves of these three electrical parameters changing with the proton fluence are obtained. Based on these curves, the attenuation amplitude of the GaInP/GaAs/Ge triple junction solar cell performance under other fluences can be estimated. According to the fitting curves of Voc, Isc, and Pm, it can be seen that Pm always attenuates most seriously under the same proton fluence.

The effects of proton irradiation on CMOS Single-Photon Avalanche Diodes (SPADs) are investigated in this article. The I–V characteristics, dark count rate (DCR), and photon detection probability (PDP) of the CMOS SPADs were measured under 30 MeV and 52 MeV proton irradiations. Two types of SPAD, with and without shallow trench isolation (STI), were designed. According to the experimental results, the leakage current, breakdown voltage, and PDP did not change after irradiation at a DDD of 2.82 × 108 MeV/g, but the DCR increased significantly at five different higher voltages. The DCR increased by 506 cps at an excess voltage of 2 V and 10,846 cps at 10 V after 30 MeV proton irradiation. A γ irradiation was conducted with a TID of 10 krad (Si). The DCR after the γ irradiation increased from 256 cps to 336 cps at an excess voltage of 10 V. The comparison of the DCR after proton and γ-ray irradiation with two structures of SPAD indicates that the major increase in the DCR was due to the depletion region defects caused by proton displacement damage rather than the Si-SiO2 interface trap generated by ionization. [ABSTRACT FROM AUTHOR]

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Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The influence of grain boundaries on deuterium (D) retention and transport was investigated in nanocrystalline tungsten (W) by exposing the samples to sub eV D atoms. Thin tungsten films with nanometer-sized grains were produced by pulsed laser deposition on tungsten substrates. Their grain size was increased up to one micrometer by thermal annealing in vacuum up to 1223 K. Irradiation damage was created by 20 MeV W ions at 290 K. The transmission electron microscopy analysis showed one order of magnitude larger dislocation density in nanometer-grained samples compared with the larger-grained samples. The samples were after W irradiation exposed to 0.3 eV D atoms at 600 K. D retention and D depth profiles were measured by nuclear reaction analysis. In the as-deposited nanometer-grained samples, D populated the damaged region more than three times faster than in the samples with larger grains, indicating that grain-boundaries increase D transport through the material. The concentration of defects was assessed by the final D concentration in the samples. The sample with the smallest grain size showed slightly larger D concentration in the irradiated area, but the difference in the D concentration was not substantial between different-grained samples. A large D concentration in the non-irradiated nanometer-grained sample was measured which is an indication for a high defect density in the initial material. From our observations, it can be postulated that the nanocrystalline microstructure did not substantially influence the generation of irradiation-induced defects by defect annihilation at grain boundaries.

The influence of grain boundaries (GBs) on the deuterium (D) transport and the creation of defects in nanocrystalline tungsten (W) films deposited on a W substrate was studied. Samples with three different grain sizes were produced for this purpose: a sample with a film having nanometer-size grains, a sample with hundred nanometer-grained film and a sample with micrometer-grained film. Samples were irradiated by 20 MeV W ions at 300 K to create displacement damage and exposed to 300 eV D ions at 450 K to populate the created and any pre-existing defects. The D transport and retention was assessed by measuring D depth profiles after certain exposure times by nuclear reaction analysis (NRA) using a 3He ion beam. From the final D concentration in the damaged area we could determine the concentration of defects that trap hydrogen, showing that the sample with the smallest grain size had the highest D concentration and it decreases with the increase of the grain size. Therefore, in nanocrystalline tungsten irradiated at 300 K, GBs do not improve radiation resistance, which would lead to fewer defects. For the first time, we show experimentally, that D transport is faster inside the nanometer-grained sample as compared to the micrometer-grained sample, meaning that D atoms have enhanced bulk diffusion along GBs. Accidentally, the film thickness was so thin that the W irradiation reached the interface between the W film and substrate, where NRA showed enhanced retention of oxygen. At that depth, two times higher D concentration was observed compared to D concentration in the damaged area in the middle of the film indicating on defect stabilization due to the presence of oxygen.

Neutron irradiation damage is a major challenge for materials employed in radiation environments, such as Reactor Pressure Vessels (RPV). Based on a determined neutron flux, the present study assesses the neutron irradiation effects via Primary Knock-on Atoms (PKAs) production, the consequent displacement damage, and gas production. The complete PKA spectra including all minor isotopes from nuclear reactions are calculated and used to estimate the displacement damage and gas production. At the inner surface of the RPV, which suffers the strongest neutron irradiation, it is found that some minor PKAs have smaller atomic numbers and higher kinetic energies than dominant isotopes in RPV. These PKAs have much deeper ranges in RPV steel and may thus produce important damage other than point defects. The displacement damage is calculated using SRIM simulations and the corresponding corrections to ensure consistency with the NRT-dpa concept. Notably, the displacement damage in the RPV should be ∼23% higher than the prediction by the NRT-dpa formula, which cannot be directly applied to PKAs different from the target atom. The 4.1 H-appm/dpa and 0.2 He-appm/dpa gas productions at the RPV inner surface are higher than that in the innermost 1/4 thickness by a factor of 2 and 1.3, respectively.

SiC devices have been typically subjected to extreme environments and complex stresses during operation, such as intense radiation and large diurnal amplitude differences on the lunar surface. Radiation displacement damage may lead to degradation or failure of the performance of semiconductor devices. In this paper, the effects of temperature and incidence angle on the irradiation cascade effect of 6H-SiC were investigated separately using the principles of molecular dynamics. Temperatures were set to 100 K, 150 K, 200 K, 250 K, 300 K, 350 K, 400 K and 450 K. The incidence direction was parallel to the specified crystal plane, with angles of 8°, 15°, 30°, 45°, 60° and 75° to the negative direction of the Z-axis. In this paper, the six types of defects were counted, and the microscopic distribution images and trajectories of each type of defect were extracted. The results show a linear relationship between the peak of the Frenkel pair and temperature. The recombination rate of Frenkel pairs depends on the local temperature and degree of aggregation at the center of the cascade collision. Increasing the angle of incidence first inhibits and then promotes the production of total defects and Frenkel pairs. The lowest number of total defects, Frenkel pairs and antisite defects are produced at a 45° incident angle. At an incidence angle of 75°, larger size hollow clusters and anti-clusters are more likely to appear in the 6H-SiC. [ABSTRACT FROM AUTHOR]

The synergistic effects on the 0.18 µm PPD CISs induced by neutron displacement damage and gamma ionization damage are investigated. The typical characterizations of the CISs induced by the neutron displacement damage and gamma ionization damage are presented separately. The CISs are irradiated by reactor neutron beams up to 1 × 1011 n/cm2 (1 MeV neutron equivalent fluence) and 60Co γ-rays up to the total ionizing dose level of 200 krad(Si) with different sequential order. The experimental results show that the mean dark signal increase in the CISs induced by reactor neutron radiation has not been influenced by previous 60Co γ-ray radiation. However, the mean dark signal increase in the CISs induced by 60Co γ-ray radiation has been remarkably influenced by previous reactor neutron radiation. The synergistic effects on the PPD CISs are discussed by combining the experimental results and the TCAD simulation results of radiation damage.

This work investigates the irradiation hardening and deuterium (D) retention behaviour of tungsten (W) under synergistic irradiations of heavy ions and D plasma. 3.5 MeV iron (Fe13+) ion irradiation was performed on recrystallized W samples (RW) to produce displacement damage of 1 dpa. Then, low-energy (38 eV) D plasma exposure was conducted at 500 K. It is found that Fe ion irradiation creates substantial vacancy-type defects and dislocation loops/networks in RW. These irradiation-induced defects not only function as nucleation sites for dislocations that increase the activation probability of new dislocations and suppress the pop-in events, but also act as barriers for dislocations that result in irradiation hardening. Nano-indentation results show that the average hardness of RW-D, RW-Fe and RW-Fe-D increases from 5.26 GPa for RW to 5.28, 6.23 and 6.56 GPa, respectively. The strong interaction between dislocations and high density of damage-induced defects is suggested to be the chief source for the obvious irradiation hardening observed in the synergistic irradiation case. Besides, compared with RW-D, the total D retention in RW-Fe-D is increased by a factor of 2.65. NRA and TDS results suggest that Fe pre-irradiation not only increases D retention within the damage layer (within the first 1.3 μm), but also enhances that beyond the damage layer (>1.3 μm) before surface blisters are formed. This work further improves the fundamental understanding on the microstructure evolution, D retention and nano-mechanical behaviour of W under synergistic irradiation effect of heavy ions and D plasma.

Radiation damage is a key challenge for materials. Accurate evaluation of radiation damage is a starting point for investigating the behaviors of materials used in a radiation environment. The present work proposes improved methods for calculating the primary radiation damage cross sections induced by light particles, including electrons, positrons, and photons. The main improvements compared with previous methods are: (1) accurate Mott cross section rather than the McKinley-Feshbach analytical approach is used for electron and positron scattering; (2) data and methods recommended by the International Commission on Radiation Unit and measurements (ICRU) are systematically applied for computing the stopping powers of electron and positron; (3) accurate differential cross section by combining different models instead of some simple approaches is used for pair production. The electron, positron, and photon irradiation-induced displacement cross sections for various important elements covering a large range of atomic numbers (from Li to U) are computed with the improved methods for energy up to 100 MeV. The calculated displacement cross sections are also tabulated so that they can be simply used for further applications. [ABSTRACT FROM AUTHOR]

In this paper, the state-of-the-art triple junction solar cell with three sub cells and two tunnel diodes is modeled using two dimensional (2D) APSYS finite element analysis software tool. The effect of electron radiation at 1 MeV and 10 MeV energies for different fluences are investigated by introducing different trap levels, trap states and trap concentrations in InGaP top and InGaAs middle sub cells. Two different structures are modeled by varying layer thickness of base and emitter of both top and middle sub cells to understand its effect on the electrical parameters and efficiency of the solar cell. The main indicative parameters - trap concentration and carrier lifetime is affected by the radiation resulting in alteration of electrical performance of solar cells. The radiation induced defects cause permanent damage to the solar cell structure and degrades the electrical performance of solar cells until its end of life (EOL). In this work, APSYS software tool is used to model radiation induced traps with different trap concentrations, generated the electrical parameters and compared with the experimental results. The results obtained from simulation are in good agreement with the experimental data. Probable traps, trap concentrations and carrier lifetime for different electron radiation energies and fluences were extracted by simulation, which can prove to be difficult to perform experimentally as only a few methods like deep level trap spectroscopy and deep level optical spectroscopy exist for deep level trap studies. This study can therefore save valuable R&D time and cost.. [ABSTRACT FROM AUTHOR]

Ni–graphene nanocomposites with high-density interfaces have enormous potential as irradiation-tolerant materials applied in Gen-IV reactors. Nevertheless, the mechanism wherein the intrinsic and/or irradiation-induced defects of graphene affect the irradiation tolerance of the composites remains poorly understood. Here, we investigate the effects of the two types of defective graphene on the displacement damage and He diffusion of the composites, respectively, using atomistic simulations. The introduction of the intrinsic defects of graphene has a significant effect on the Ni lattice structure near the Ni–graphene interface, especially showing that after displacement cascades, the number of defects gradually increases with the increase in graphene-defective size due to the formation and growth of stacking fault tetrahedra. The existence of the irradiation-induced defects of graphene does not diminish the ability of the interface to trap He atoms/clusters and even may be maintained or improved, mainly reflected in the fact that many isolated He atoms and small clusters can gradually migrate toward the interface and the fraction of He within the interface is up to 37.72% after 1 ns. This study provides an important insight into the understanding of the association relationships of defective graphene with the irradiation tolerance of composites. [ABSTRACT FROM AUTHOR]

SiC devices have been typically subjected to extreme environments and complex stresses during operation, such as intense radiation and large diurnal amplitude differences on the lunar surface. Radiation displacement damage may lead to degradation or failure of the performance of semiconductor devices. In this paper, the effects of temperature and incidence angle on the irradiation cascade effect of 6H-SiC were investigated separately using the principles of molecular dynamics. Temperatures were set to 100 K, 150 K, 200 K, 250 K, 300 K, 350 K, 400 K and 450 K. The incidence direction was parallel to the specified crystal plane, with angles of 8°, 15°, 30°, 45°, 60° and 75° to the negative direction of the Z-axis. In this paper, the six types of defects were counted, and the microscopic distribution images and trajectories of each type of defect were extracted. The results show a linear relationship between the peak of the Frenkel pair and temperature. The recombination rate of Frenkel pairs depends on the local temperature and degree of aggregation at the center of the cascade collision. Increasing the angle of incidence first inhibits and then promotes the production of total defects and Frenkel pairs. The lowest number of total defects, Frenkel pairs and antisite defects are produced at a 45° incident angle. At an incidence angle of 75°, larger size hollow clusters and anti-clusters are more likely to appear in the 6H-SiC.

Space radiation can affect the performance and reliability of components in space systems. This paper focuses on the investigation of three types of radiation damage including ionizing dose, displacement damage, and single event damage using OMERE software. Considering the outputs of this software, how to use and use a variety of electronic components with different commercial, military and space grades in LEO and GEO satellites is discussed. These components have the least risk of displacement damage. Mass budget constraints should also be considered when using commercial components in the GEO circuit. The maximum thickness for the safety of components in LEO and GEO circuits is 2.6 mm and 9.5 mm respectively. Given the inability of SEE damage to increase in thickness, the best solution to this damage is to use radiation-resistant solutions, especially software issues.

The interaction mechanism between displacement damage and ionization damage in SiO2 layer has been researched on gate-controlled lateral p-n-p transistor (GLPNP). The sequential irradiation experiments of 400-keV O ions with high dose rate $\gamma $ -rays were carried out, and the degradation and defect evolution results of the device were analyzed by the reciprocal change of current gain change, gate sweep (GS) curve, and deep level transient spectrum (DLTS) results. The results show that there is a negative direct synergistic effect between 400-keV O ions and Co- $60~\gamma $ -rays in GLPNP. At the same time, combined with the GS curve and DLTS results, it can be concluded that the displacement defects of 400-keV O ions in SiO2 layer of GLPNP transistors will capture the holes generated by Co- $60~\gamma $ -rays, thus forming a large number of positive oxide charges ($N_{\mathrm {ot}}$). These $N_{\mathrm {ot}}$ are like “space charge wall,” hindering the movement of protons and holes to the Si/SiO2 interface, and thus inhibiting the generation of interface trap ($N_{\mathrm {it}}$). Due to the decrease of $N_{\mathrm {it}}$ and the increase of positive $N_{\mathrm {ot}}$ , the damage of transistor is weakened. The experimental results show the effects of displacement damage on the ionization effect in SiO2 layer and, more important, provide direct evidence for the space charge model. [ABSTRACT FROM AUTHOR]

The nonionizing energy loss (NIEL) concept, introduced more than 40 years ago, is still used to characterize the damage generated by different particles and $\gamma $ -rays. Its continuing relevance is due to the experimentally established scaling in the creation rate of defects by radiation of different types. NIEL calculations are quite simple, based on classical physics. We thus name them classical NIEL, NIELc. Their calculation depends on an $a$ priori known $E_{d}$ -displacement threshold energy in monoatomic materials. For the compound semiconductor materials studied here, Ga $X$ and In $X$ , where $X$ are the cations N, P, As, Sb, the experimental $E_{d}$ values vary over a wide range and only approximate values for NIELc can be calculated. Thanks to some recent studies carried out using the molecular dynamic (MD) method, the NIEL values were estimated using atomic scale calculations. Consequently, we can now compare NIELc with more precise data. These data also include the “dynamic” behavior of the NIEL, which is related to the annealing of the damage (like Frenkel pair recombination) and the generation of extended crystalline defects. The NIEL calculated using the MD method is referred to in the literature as NIELeff. A detailed comparison between NIELc and NIELeff as a function of electron and proton energies is made here. It shows that the difference between the two quantities is not large and cannot influence the dependence of NIEL on temperature and different radiation types. Both yield similar results in calculating the effect of displacement damage. As an additional use of NIELc, we analyze its application to estimate the relative tolerance of the different members of the Ga $X$ and In $X$ families to radiation defects as a function of particle energies. [ABSTRACT FROM AUTHOR]

Single crystalline tungsten was irradiated by the medium-mass ion Si with 7.5 MeV and high mass-ion W with 20.3 MeV up to a calculated peak damage level of 0.04 dpa and 0.5 dpa. The obtained dislocation structure of the damage zone was investigated by transmission electron microscopy and systematically compared with each other. Bright-field kinematical images were taken under four different two-beam diffraction conditions g = âˆ'200, 020, âˆ'110, 110 close to the [100] zone axis. The observed damage depth and damage peak position is in good agreement with the SRIM calculated damage depth profiles. The dislocation structures were investigated at the region of the damage peak because there the damage levels are comparable. In both irradiations (Si and W), the dislocation structures were similar. At the low damage level of 0.04 dpa dislocation loops and dislocation-loop clusters were found. The size of the dislocation loops in the W-irradiated tungsten sample was up to 20% higher than for the Si-irradiated sample. At the high damage level of 0.5 dpa a dislocation network consisting of dislocation-loop chains and dislocation lines was found for both irradiations. The dislocation line density was about 12% higher for the W-irradiated sample. Through comparison of the damage zone to SRIM damage depth profiles it was found that the transition from dislocation loops and dislocation-loop clusters to an ordered dislocation network takes place at about 0.08â€"0.1 dpa. Despite the large differences in ion mass and irradiation energy the dislocation structures were very similar. [ABSTRACT FROM AUTHOR]

The remote sensing and satellite community working for space organizations have expressed interest in building advanced devices with potential choices for Gallium Nitride based transistors. Radar and satellite communication applications employ nitride High Electron Mobility Transistors (HEMTs) due to their high radiation-absorbing and temperature tolerant qualities. However, they also deteriorate simultaneously upon such radiations that cause a drastic fall in their lifetimes. This article carries out reliability studies of GaN-based III-V semiconductor devices, including HEMTs, Schottky and thin film diodes by reviewing the defects induced by radiation. A review of the various kinds of defects induced in these devices upon subject to several radiation beams like proton, neutron, gamma, alpha, and other sources has been discussed here. GaN, when subject to high energy ionizing radiation particles, produce point defects in the material that are more dominated by extended disordered regions. Trap states also occur as a part of radiation damage with forbidden gaps consisting of deep thermal ionization energies, which causes the device's mobility and electrical conductivity to decrease drastically. A short description on how these defects can be mitigated to a certain extent has been given, eying towards more withstanding capabilities for these devices in radiation-hardened environments. • A study into the effects of GaN III-V devices upon ionizing radiation is given. • Effects such as TID, DD and SEE have been investigated comprehensively. • Deficiencies like vacancies, trap state formations, has been addressed. • Certain variables, like fields and contact resistance, show less noticeable shift. • GaN's ability in controlling high energy radiation-hard devices is also reviewed. [ABSTRACT FROM AUTHOR]

Based on carbon nanotube (CNT) field-effect transistors (FETs), integrated circuits in next generation have broad application prospects in space exploration. However, the displacement damage (DD) effect is considered as an important factor which limits the performance of CNTFETs. In this study, the local bottom-gate CNTFETs with different channel sizes have been irradiated by highly charged ions (HCI)-132Xe20+ with of energy 5 MeV, the fluences ranged from 1 × 1011 ions/cm2 to 2 × 1015 ions/cm2. At low fluences (1 × 1011, 1 × 1012 and 1 × 1013 ions/cm2), the on/off ratio and transconductance of CNTFETs decreased, and the threshold voltage shift negatively. The reason was HCI introduced defects in the gate dielectric and CNT layer, resulting in reducing carrier mobility, thereby decreasing the on/off ratio and transconductance of CNTFETs. In addition, the interface states and bulk traps in the gate dielectric layer would capture ionized holes to form charge state defects, causing the threshold voltage to shift negatively, and the degree of drift was related to the channel size L / W. At high fluences (1 × 1014, 1 × 1015 and 2 × 1015 ions/cm2), the source and drain of CNTFETs were turned on, the device failed, and the gate leakage current increased. As the irradiation fluence increased, the D-band appeared in the Raman spectrum of SWCNT, the intensity ratio of the D-band and the G+-band increased, and the linear shape of the G--band changed. The irradiation fluence exceeded 1 × 1013 ions/cm2, the Raman peaks overlapped, and the SWCNT became amorphous. AFM images showed that when the irradiation fluence was 1 × 1013 ions/cm2, the SWCNT was complete. When the fluence was increased to 1 × 1015 ions/cm2, the SWCNT was broken. The study showed that the DD tolerance of CNTFETs could reach 1 × 1013 ions/cm2, which proved the excellent radiation resistance of CNTFETs and provided a reference for the radiation resistance of CNT-based microelectronic devices. [ABSTRACT FROM AUTHOR]

This article investigates the displacement damage on AlGaN/GaN high-electron-mobility transistors (HEMTs) using the 30-MeV fluorine ions. The electrical degradation and the defects in HEMTs were examined before and after irradiation. Three defect states are detected in a deep-level transient analysis system (DLTS), including a broad surface state peak ($N_{1}$) and two bulk defect peaks ($H_{1}$ and $H_{2}$). The energy levels of these two defects are $E_{\mathrm {C}} 0.63$ eV ($H_{2}$) and $E_{\mathrm {C}} 0.91$ eV ($H_{1}$), respectively. There is a linear relationship between the concentration of $H_{1}$ and the fluorine ion fluence. The radiation damage and electrical performance degradation of AlGaN/GaN HEMTs are simulated by combining with simulation software of different methods. The calculated results are in agreement with the experimental data. The performance degradation caused by heavy ion of the device is mainly caused by the $H_{1}$ defect. The effect of defects with shallow energy level is shielded by the Fermi-level pinning in deeper energy level. Moreover, the defect distribution of GaN in AlGaN/GaN heterojunction plays a major role. It is found that the method of combining experimental data with multiscale simulation is an effective way to predict the radiation damage of devices. [ABSTRACT FROM AUTHOR]

Gallium nitride (GaN) has attracted great attention as a structural material for advanced microelectromechanical systems (MEMS), thanks to its excellent ensemble of electrical and mechanical properties. Here, we report on studying the effects of ion radiation-induced displacement damage on resonant MEMS made of GaN film grown on aluminum nitride (AlN) buffer layer. We design and fabricate GaN/AlN heterostructure doubly-clamped microstring resonators with length $L \,\, =100$ , 200, 300, 400, 500, 600, and 700 $\mu \text{m}$ , and irradiate the devices with 440-keV Ar $^{+}$ ions, to probe the effects of ion radiation-induced displacement damage on the resonance behavior. The ion energy and range have been selected so that the ions would stop within the GaN layer, thus allowing diagnostics to show the effects of damage in the structure. The multimode resonance frequencies of the devices decrease significantly ($\vert \Delta f\vert /f >50$ %) with the increase of fluence beyond 1014 cm−2. According to scanning electron microscopy (SEM) imaging, the irradiated GaN/AlN resonators are visibly deformed at high fluence, where the amount of curvature increases monotonically with the fluence. The deformation of the structures can be ascribed to the change in both Young’s modulus and built-in stress resulting from ion radiation-induced displacement damage. The results extend the understanding of radiation-induced damage mechanisms in resonant MEMS. [ABSTRACT FROM AUTHOR]

Integrated silicon microwave pin diodes are exposed to 10-keV X-rays up to a dose of 2 Mrad(SiO2) and 14-MeV fast neutrons up to a fluence of $2.2\,\,\boldsymbol {\times }\,\,10\,\,^{\mathrm{ 13}}$ cm−2. Changes in both dc leakage current and small-signal circuit components are examined. Degradation in performance due to total-ionizing dose (TID) is shown to be suppressed by non-quasi-static (NQS) effects during radio frequency (RF) operation. Tolerance to displacement damage from fast neutrons is also observed, which is explained using technology computer-aided design (TCAD) simulations. Overall, the characterized pin diodes are tolerant to cumulative radiation at levels consistent with space applications such as geosynchronous weather satellites. [ABSTRACT FROM AUTHOR]

The presence of ionizing radiation in the space environment, due to trapped particles, solar particles and cosmic rays can be a serious threat to the proper functioning of electronic components used in satellites and spacecraft. In this work, the leakage current variation of a silicon diode, as the basic element of many electronic components, has been investigated in the exposure of space protons. For this purpose, the GEANT4 Monte Carlo code has been used to calculate the non-ionizing energy loss in the device. The simulation of electrical parameters for irradiation of space protons were also done by SILVACO software. The results show that the leakage current increases by about 1.85 times the amount of it before irradiation, up to about 96.2 nA/μm by the increase in the proton flux up to 2.1×1012 p/cm2. Irradiation of BPW34 photodiodes under 30 MeV protons was performed to validate the results of simulation.

Understanding radiation effects on avalanche photodiodes (APDs) is important because they are used in several applications involving harsh radiation environments. APDs are used as photosensors in applications where speed and detection efficiency are critical. Proton irradiation experiments on a commercial off-the-shelf APD demonstrated that the irradiation flux and applied reverse bias have a strong influence on the severity of radiation effects. This is measured using the ion beam induced charge (IBIC) technique in which charge collection efficiency (CCE) describes the signal response from a device. CCE can degrade substantially due to radiation damage, but recent measurements show that certain combinations of irradiation flux and reverse bias can lead to increases in CCE up to 186% ± 24% for irradiations with 2 MeV protons at a fluence of $6.4\times 10^{11}$ cm−2. This defect-enhanced charge multiplication (DECM) only appeared when the reverse bias during irradiation ranged from 170 to 1830 V out of a maximum operating bias of 2000 V and the proton flux ranged from $9.8\times 10^{7}$ to $3.4\times 10^{9}$ cm−2s−1. Values outside of either range led to losses in CCE. It is expected that DECM should be encountered in other devices, especially those with sufficiently high electric fields to cause impact ionization. [ABSTRACT FROM AUTHOR]

The effective dopant concentration in p-type Si detectors reduces with irradiation fluence at low fluences due to the acceptor removal process, which degrades detector performance and shortens its lifetime. This effect has been experimentally characterized and parametrized, but its microscopic origin is still unknown. We use atomistic simulations to gain insight into acceptor removal in neutron irradiation by modeling damage generation and defect-dopant interactions. We analyze the effect on dopant deactivation of the Si di- and tri-interstitial diffusion, the inhomogeneity of irradiation damage and the wafer temperature rise during irradiation. We characterize defect generation rates and identify the relevant defect-dopant interactions. Acceptor removal occurs mainly through the formation of B i pairs and small boron-interstitial clusters, and it is limited by the availability of mobile Si interstitials. The presence of impurities (O, C) modifies B-complexes favoring the formation of B i O, but has a limited effect on the amount of removed acceptors. [ABSTRACT FROM AUTHOR]

Spin–orbit torque magnetic tunnel junction (SOT-MTJ) is the memory cell of magnetic random access memory (MRAM), which is a promising candidate for upper level cache in the harsh environment due to nonvolatility, high speed, and high endurance. Therefore, it is significant to research the mechanism of irradiation effects on the SOT-MTJ before its integration onboard. This article investigates the ionization and displacement damage of in-plane magnetic anisotropy SOT-MTJ, including 1-MeV electron and 17.2-keV He+ and 60Co gamma irradiations with various fluences and doses, respectively. The devices are resilient to tunnel magnetoresistance (TMR), whereas the magnetic properties are changed after irradiation. The 100-Mrad (Si) gamma and 17.2-keV He+ irradiations generate similar damages on the device performances, in the aspects of the magnetic anisotropy and critical current density ($J_{\mathrm {c}}$). However, the displacement damage originating from the electron irradiation does not have a significant influence on $J_{\mathrm {c}}$. In addition, the saturation magnetization and exchange bias field are changed by irradiations without regularity. Some possible mechanisms are discussed to explain the experimental results through the simulation of stopping and range of ions in matter (SRIM) and microstructural tests. [ABSTRACT FROM AUTHOR]

The MOS-controlled Thyristor (MCT) has been characterized by MOS-gating, high current rise rate, and high blocking capability. The anode short MCT (AS-MCT) is distinguished from conventional MCT by an anode-short structure, which develops a normally-off characteristic. As a composite structure made of metal-oxide-silicon and bipolar junction transistors, AS-MCT is susceptible to displacement damage induced by energetic radiation. The anode trigger current which denotes the latch-up of internal thyristor structure is a key parameter for AS-MCTs. From the aspects of devices physics, we propose a model to describe the displacement damage on trigger current. Our model provides an excellent fit to the experimental data of the AS-MCT samples subjected to fission neutrons with flux in the range of $3.1\times 10^{9}-5.5\times 10^{13}\,\,\mathrm {cm}^{-2}$ . Moreover, this work shows that the high injection effect can alleviate the displacement damage of trigger current following high flux exposures.

Nanoindentation of ion-irradiated nuclear structural materials and model alloys has received considerable interest in the published literature. In the reported studies, the materials were typically exposed to irradiations using a single ion energy varying from study to study from below 1 MeV to above 10 MeV. However, systematic investigations into the effect of self-ion energy are still insufficient, meaning that the possibilities to gain insight from systematic energy variations are not yet exhausted. We have exposed pure Fe, ferritic Fe-9Cr, martensitic Fe-9Cr and the ferritic-martensitic reduced-activation steel Eurofer 97 to ion irradiations at 300°C using 1, 2 and 5 MeV Fe2+ ions as well as 8 MeV Fe3+ ions and applied nanoindentation, using a Berkovich diamond indenter, to characterize as-irradiated samples and unirradiated references. The effect of the ion energy on the measured nanoindentation response is discussed for each material. Two versions of a primary-damage-informed model are applied to fit the measured irradiation-induced hardening. The models are critically compared with the experimental results also taking into account reported microstructural evidence. Related ion-neutron transferability issues are addressed.

Ni–graphene nanocomposites with high-density interfaces have enormous potential as irradiation-tolerant materials applied in Gen-IV reactors. Nevertheless, the mechanism wherein the intrinsic and/or irradiation-induced defects of graphene affect the irradiation tolerance of the composites remains poorly understood. Here, we investigate the effects of the two types of defective graphene on the displacement damage and He diffusion of the composites, respectively, using atomistic simulations. The introduction of the intrinsic defects of graphene has a significant effect on the Ni lattice structure near the Ni–graphene interface, especially showing that after displacement cascades, the number of defects gradually increases with the increase in graphene-defective size due to the formation and growth of stacking fault tetrahedra. The existence of the irradiation-induced defects of graphene does not diminish the ability of the interface to trap He atoms/clusters and even may be maintained or improved, mainly reflected in the fact that many isolated He atoms and small clusters can gradually migrate toward the interface and the fraction of He within the interface is up to 37.72% after 1 ns. This study provides an important insight into the understanding of the association relationships of defective graphene with the irradiation tolerance of composites.

Radiation effects studies on a commercial beveled-edge avalanche photodiode (APD) showed that applying reverse bias to the device during irradiation enhanced the severity of apparent damage. Proton microbeam irradiations were made using a proton beam energy of 2 MeV and fluence ranging from 2.0 × 1010 to 5.1 × 1012 cm−2. Charge collection measurements using the ion beam induced charge (IBIC) technique showed that relative losses increased by up to an order of magnitude when the reverse bias applied during irradiation increased from 50 to 1500 V. The presence of reverse bias also led to equivalent losses in charge collection that would only be seen in irradiations with an order of magnitude higher fluence in unbiased APDs. The results demonstrate that bias-enhanced irradiation damage is insufficiently understood and must be accounted for in characterizations of radiation effects. [ABSTRACT FROM AUTHOR]

As a strong candidate for the new type of non-volatile memories and artificial synaptic devices, memristor has a huge development prospect in aerospace, Mars exploration and other space science and application fields. Once large-scale application of memristor requires extremely stringent radiation resistance performance for the memristors. In order to improve the radiation resistance of memristors, it is necessary to explore the radiation effect mechanism and develop an effective radiation resistance technology. This paper summarizes the research status and trends of irradiation effects on memristors, describes the mechanism and analysis method of irradiation damage of memristor, and focuses on the irradiation effects of the memristors with transition metal oxide material system. Additionally, the possibility of scientific problems and key technologies are discussed, so as to provide some ideas for the radiation hardening and space application of memristor.

Positron Annihilation Technique is very sensitive to vacancy defects and small vacancy clusters and has been used as supplementary for TEM in radiation damage research. In this paper, we evaluated the displacement damage in solids induced by positrons and its effect on defects measurement, which has not been considered carefully in most PAT application. Displacement damage could only be produced when kinetic energy of positron exceeds a threshold determined by average displacement energy and the mass of atoms. Based on the latest models of displacement damage and numerical Mott elastic differential cross section of positrons interacting with atoms, displacement cross section for fast positron in solids was calculated and compared with that for electrons. In the energy range from 1 MeV to 100 MeV, electrons will produce more displacement defects than positrons do, especially in high-Z materials. Number of total defects depends on the primary displacement cross section and the size of damage cascades. To get distributions of defects and terminating position of positrons in materials, a Monte Carlo tool with full damage model was developed and validated. From the results of Monte Carlo modeling, the defects -generated by mono-energy positron beam have shallower distribution than the stopping position of positrons, indicating separation of defects and positrons and this fact benefits defects measurement because displacement damage produced by fast probing positron beam have little affection on the measurement. But for the positron beams from radioactive sources (such as 22Na and 64Cu) with continuous energy spectrum (from 0 to Emax), the depth profile of defects and terminated position of positrons overlap with each other and this fact indicated that defects measurement in materials will be affected by extra defects produced by positrons. The density of defects produced by positron beam is quite low with a typical value of about 0.01–0.1 cm−3 per positron in low-Z materials, which could be comparable with the defect density limitation if enough accumulated positrons are implanted into materials during measurement. For commonly used structural metals (such as Fe, Mn, Cu and metals with Z number higher than 40), using positron from 22N and 64Cu directly to measure defects density is quite safe because the energy is smaller than the displacement threshold.

The high stochasticity of collision cascades makes running large sets of molecular dynamics simulations mandatory to obtain meaningful statistics. The convergence of the number of defects and of clusters and of the Primary Knock-On Atom (PKA) penetration depth with respect to the number of simulations in the sets is investigated for PKAs of 1 keV and 5 keV in Si. Two methods for setting the initial directions of the PKAs are compared: one is entirely based on randomness and the other integrates symmetry considerations. The latter method eases the convergence of the results. Larger sets are needed to converge the PKA depth than the number of clusters and defects. We observe that the higher the energy of the PKA, the harder it gets to reach the convergence. We find that large sets of simulations enables to get rid of the influence of the initial position of the PKA. [ABSTRACT FROM AUTHOR]

We develop methods for bounding part-to-part variation in total ionizing dose (TID) data. When used in conjunction with statistical radiation environment models, these methods allow development of RHA that deliver estimated piece part reliability for any desired confidence level (CL), moving beyond risk avoidance methodologies based on a radiation design margin. Two methods are developed, and their results compared for realistic data. [ABSTRACT FROM AUTHOR]

To explore the role of hydrogen in radiation degradation of AlGaN/GaN high-electron-mobility transistors (HEMTs), the performance degradation of the hydrogen untreated and pretreated devices is compared under the exposure of carbon ions. The energy of carbon ions is chosen as 7.6 MeV, and the maximum fluence reaches 4 × 1012 cm−2. By electrical character measuring, it is found that the positive shift of the threshold voltage and the decrease of the transconductance occur after to the irradiation. Hydrogen pretreatment accelerates the shift of threshold voltage and the decrease of the transconductance. The threshold voltage of the device is almost unchanged under 1-MeV electron irradiations. This means that the displacement damage leads to the shift of the threshold voltage. The height of Schottky barrier hardly changes in the hydrogen pretreated devices, showing that the ionization defects such as the formation of interface states under the gate are not the main cause of device degradation. Deep level transient spectrum (DLTS) results show that the irradiations cause the increase of gallium vacancies, and the hydrogen pretreatment inhibits its formation. According to the first principle calculation, the existence of hydrogen in GaN layer can reduce the formation energy of and the number of charges of the defects. It is speculated that hydrogen atoms participate in the evolution of radiation defects, which changes the types and number of defects in the devices. [ABSTRACT FROM AUTHOR]

The electrical degradation in AlGaN/GaN high-electron-mobility transistors (HEMTs) is examined under irradiation with 7.6-MeV carbon (C), 20-MeV oxygen (O), and 30-MeV fluorine (F) ions in situ. To characterize the radiation damage in the HEMTs, the ionizing dose Di, displacement dose Dd, and number of vacancies versus the chip depth in the devices have been calculated for heavy ions. As expected, in all three types of HEMTs, the output current decreases more than 30% and threshold voltage positive shifts after the irradiation fluence of 4 × 1012 ions/cm2. The performance degradation of AlGaN/GaN HEMTs is caused by radiation-induced charged defects. Based on calculation and experimental results, it is shown that the nonionizing energy loss (NIEL) method is not suitable for estimating the degradation of AlGaN/GaN HEMTs either considering gallium vacancy or considering both gallium vacancy and nitrogen vacancy. In the same displacement damage dose, the threshold voltage degradation rate depends on the type of incident particles and independent of the channel length. The damage caused by carbon ions is the smallest and the damage caused by fluoride ions is the largest. [ABSTRACT FROM AUTHOR]