MeV Proton Irradiation Research Articles

Reducing proton radiation vulnerability in AlGaN/GaN high electron mobility transistors with residual strain relief

Strain plays an important role in the performance and reliability of AlGaN/GaN high electron mobility transistors (HEMTs). However, the impact of strain on the performance of proton irradiated GaN HEMTs is yet unknown. In this study, we investigated the effects of strain relaxation on the properties of proton irradiated AlGaN/GaN HEMTs. Controlled strain relief is achieved locally using the substrate micro-trench technique. The strain relieved devices experienced a relatively smaller increase of strain after 5 MeV proton irradiation at a fluence of 5 × 1014 cm−2 compared to the non-strain relieved devices, i.e., the pristine devices. After proton irradiation, both pristine and strain relieved devices demonstrate a reduction of drain saturation current (Ids,sat), maximum transconductance (Gm), carrier density (ns), and mobility (μn). Depending on the bias conditions the pristine devices exhibit up to 32% reduction of Ids,sat, 38% reduction of Gm, 15% reduction of ns, and 48% reduction of μn values. In contrast, the strain relieved devices show only up to 13% reduction of Ids,sat, 11% reduction of Gm, 9% reduction of ns, and 30% reduction of μn values. In addition, the locally strain relieved devices show smaller positive shift of threshold voltage compared to the pristine devices after proton irradiation. The less detrimental impact of proton irradiation on the transport properties of strain relieved devices could be attributed to reduced point defect density producing lower trap center densities, and evolution of lower operation related stresses due to lower initial residual strain.

Open volume defect accumulation with irradiation in GaN, GaP, InAs, InP, Si, ZnO, and MgO

Vacancies are generated in semiconductor devices while operating in the space radiation environment, impacting semiconductor carrier concentrations and dynamics. Positron annihilation lifetime spectroscopy (PALS) is used to probe these defect concentrations in bulk grown GaN, GaP, InAs, InP, Si, MgO, and ZnO both as-grown and as a function of 2–4 MeV proton irradiation. All samples were irradiated to yield a common initial damage production and characterized identically. In as-grown samples, PALS reveals vacancy concentrations above the saturation limit in the oxides, disabling further analysis. As a function of dose, of the materials in which defect accumulation could be probed, it is observed that GaN is the most resistant to the accumulation of defects (attributed to the Ga vacancies) and Si is the least. GaP (attributed to the Ga vacancy) and InAs exhibit slightly higher rates of vacancy accumulation than GaN. InP exhibits high defect accumulation rates approaching that of Si. This information is key to understanding the operation of a diverse set of semiconductors in the space radiation environment.

The effects and mechanisms of 2 MeV proton irradiation on high bias conditions of InP/InGaAs DHBTs

In this work, a 2 MeV proton irradiation experiment has been carried out on self-fabricated InP/InGaAs heterojunction bipolar transistors (HBTs) with fluence of 5 × 1013 H+/cm2 and 1 × 1014 H+/cm2. The degradation and mechanisms have systematically been studied under different bias conditions. The irradiated InP-based HBTs have suffered more sever degradation at low and high bias voltages with larger damage coefficient of current gain (Kβ), due to the increased base recombination current and the slacken collector current respectively. Under high injection current densities, the slow-down of collector current and the collapse of current gain (β) have occurred at increasingly smaller biases as irradiation fluence increases. Consistently, the ideality factor of base current collapses to 1 at high injection current, moreover, the collapse point decreases as fluence increases. The aggravated degradation at high current densities is attributed to the influence of heterojunction barrier effect (HBE) by the structure of the multi-layer collector region. The study would be of great significance for optimizing the device structure and improving the irradiation tolerance.

Study of displacement damage effects in InGaAs PIN photodiode under 10 MeV proton irradiation

The displacement damage effect of 10 MeV proton radiation on a high-speed InGaAs PIN photodiode has been experimentally investigated to evaluate the stability of the device in a space radiation environment. The results show that the dark current and low-frequency noise of the device increase significantly after irradiation, while the capacitance of the device decreases slightly after irradiation, where the spectral response parameters are less affected by irradiation. The increase in dark current is essentially linear with the displacement damage dose. Finally, the effect of proton irradiation on the optical communication system is simulated and the results show that the bit error rate of the system increases with the increase in irradiation fluence, which seriously affects the sensitivity of the optical communication system.

High-Energy Radiation Effects on Silicon NPN Bipolar Transistor Electrical Performance: A Study with 1 MeV Proton Irradiation.

This study investigates the degradation of the silicon NPN transistor's emitter-base junction, specifically the 2N2219A model, under both forward and reverse polarization. We examine the current-voltage characteristics under the influence of 1 MeV proton irradiation at various fluencies, which are 5.3×108,5.3×1010,5×1011,5×1012, and 5×1013 protons/cm², all conducted at 307 K. The experimental findings elucidate a pronounced dependency of diode parameters, including the reverse saturation current, series resistance, and the non-idealist factor, on the incident proton flow. This observation underscores that proton-induced degradation is primarily driven by displacement damage, while recorded degradation is predominantly attributed to the generation of defects and interfacial traps within the transistor resulting from exposure to high-energy radiation. Our findings indicate that the effects of irradiation align more closely with the compensation phenomenon in doping rather than its reinforcement.

Proton Irradiation‐Induced Displacement Damage in 650 V Si and SiC Power Diodes

A comparison of the displacement damage effects in Si and silicon carbide (4H‐SiC) commercial diodes due to 6 MeV proton irradiation is presented. The devices chosen for this study are rated at 650 V/8 A, making them technological alternatives of each other. It is found that Si diodes degrade ≈4.6 times faster than the SiC counterparts under forward biasing. In addition, the leakage current for the SiC diode in reverse mode decreases due to proton irradiation, whereas it increases for the Si diode under the same conditions. The difference in the behavior of both the diodes, as a result of the irradiation process, is discussed in terms of the induced deep‐level defects. The results show that SiC diodes are more resistant to displacement damage caused by proton irradiation than Si devices, with the same specifications.

Radiosensitizing Effect of Dextran-Coated Iron Oxide Nanoparticles on Malignant Glioma Cells.

The potential of standard methods of radiation therapy is limited by the dose that can be safely delivered to the tumor, which could be too low for radical treatment. The dose efficiency can be increased by using radiosensitizers. In this study, we evaluated the sensitizing potential of biocompatible iron oxide nanoparticles coated with a dextran shell in A172 and Gl-Tr glioblastoma cells in vitro. The cells preincubated with nanoparticles for 24 h were exposed to ionizing radiation (X-ray, gamma, or proton) at doses of 0.5-6 Gy, and their viability was assessed by the Resazurin assay and by staining of the surviving cells with crystal violet. A statistically significant effect of radiosensitization by nanoparticles was observed in both cell lines when cells were exposed to 35 keV X-rays. A weak radiosensitizing effect was found only in the Gl-Tr line for the 1.2 MeV gamma irradiation and there was no radiosensitizing effect in both lines for the 200 MeV proton irradiation at the Bragg peak. A slight (ca. 10%) increase in the formation of additional reactive oxygen species after X-ray irradiation was found when nanoparticles were present. These results suggest that the nanoparticles absorbed by glioma cells can produce a significant radiosensitizing effect, probably due to the action of secondary electrons generated by the magnetite core, whereas the dextran shell of the nanoparticles used in these experiments appears to be rather stable under radiation exposure.

Effects of 63 MeV proton irradiation on the performance of MWIR InGaAs/InAsSb nBn photodetectors

An investigation into the effects of 63 MeV proton irradiation on high-sensitivity mid-wave infrared InGaAs/InAsSb nBn devices is performed. Three different structures with various absorber region doping profiles are irradiated and characterized to assess their impact on performance degradation. Minority carrier lifetime is measured using time-resolved photoluminescence and lifetime damage factors are assessed. The majority carrier concentration is determined via capacitance–voltage measurements and dopant introduction rates are calculated. An analysis of dark current density is performed using these material parameters, revealing a reduction in mobility with proton fluence and the emergence of a proton-induced trap energy level. Quantum efficiency is calculated at each proton fluence, and quantum efficiency damage factors show that the graded doping structure exhibits the least reduction of quantum efficiency with dose, attributed to its effective mobility enhancement. Conclusively, detector sensitivity, assessed via shot-noise limited noise-equivalent irradiance, shows that the graded doping structure is the least susceptible to high energy proton irradiation-induced performance degradation.

Degradation characteristics and equivalent analysis of InGaAsP space solar cells under proton and neutron irradiation

The effects of 2 MeV, 30 MeV proton and neutron irradiation on the performance of InGaAsP single junction solar cells were investigated. The degradation of electrical and optical properties was studied by experiment, such as I-V curve, external quantum efficiency, photoluminescence (PL) and scanning electron microscopy (SEM). Results show that the performance parameters of the solar cell degrade seriously with the increasing of the displacement damage dose. The PL results indicate that irradiation has a destructive effect on the photoelectric properties of materials. The carrier parameters were quantitatively calculated according to the PL normalized peak. The minority carrier lifetime attenuation model and equivalent displacement damage model were established to evaluate the on-orbit behavior of the InGaAsP solar cell.

Peak effects induced by particle irradiations in 2H-NbSe2

Various peak effects in 2H-NbSe2 single crystals induced by particle irradiations were studied. 3 MeV proton irradiation magnified the peak effect induced by order–disorder (O-DO) transition of vortices, where the peak field shifts from high fields to low fields with increasing irradiation dose. For the peak effect in NbSe with splayed columnar defects (CDs), as the splayed angle increases, peak field gradually shifts from high fields to low fields. Numerical calculations have been conducted to investigate the mechanism of the peak effect. The calculated results exhibit excellent agreement with experimental observations. Analyses of field dependence of J reveal the formation of non-uniform J flow with increasing splayed angle, which plays a crucial role in inducing the self-field peak effect in superconductors with splayed CDs. In samples with symmetric splayed CDs with respect to the c-axis generated by 800 MeV Xe and 320 MeV Au ions, coexistence of O-DO transition-induced peak effect and self-field peak effect was observed. In the case of 320 MeV Au irradiated samples, when the splay angle is small, the two peak effects transform into a broad peak, which has similarity to the anomalous peak effect observed in iron-based superconductors. Interestingly, the broad anomalous peak effect is strongly suppressed when the external magnetic field is applied parallel to one of splayed CDs.

Super antiwear properties of polytetrafluoroethylene (PTFE) induced by MeV proton irradiation

In this paper, the surface of polytetrafluoroethylene (PTFE) was modified by 1 MeV proton beam at high temperature. The changes of wear resistance and hardness of PTFE before and after irradiation were evaluated by ball/pin disk friction loss tester and nanoindentation tester, respectively. The results showed that the wear resistance of PTFE irradiated by proton at high temperature has been significantly enhanced. The mass wear rate decreases from 2.75 × 10−6 g/Nm to 0.39 × 10−6 g/Nm, and the wear depth decreases from 29.9 μm to 8.2 μm, respectively. Proton irradiation could be a simple and effective method for PTFE surface modification and can significantly improve the wear resistance. The potential chemical reaction mechanism for the improvement of wear resistance of irradiated PTFE in terms of microstructure was discussed. Crosslinking induced by proton irradiation enhanced the interaction force among PTFE molecules, thus the mechanical properties were improved.

The effect of secondary phases on microstructure and irradiation damage in an as-built additively manufactured 316 L stainless steel with a hafnium compositional gradient

Additive manufacturing (AM) or rapid prototyping has become a crucial tool for reducing both cost and time while increasing efficiency in qualifying structural materials for reactor use. In this study, directed energy deposition (DED) was used to develop an as-built 316 L stainless steel sample with three regions of increasing Hf-dopant to study the effects of Hf on the irradiation response of the material. Morphological and microstructural changes were analyzed before and after 2 MeV proton irradiation at 360 °C to a damage of 2.5 dpa at ∼ 10 µm below the surface. The addition of Hf effectively suppressed radiation-induced damage (dislocation loops, radiation-induced segregation) due to enhanced point defect recombination. The radiation damage seen in the as-built sample was further compared to a thermo-mechanically treated counterpart of the same fabrication and irradiation parameters which was found to behave superiorly. The increased radiation resistance of this material may be attributed to the as-built microstructure, which includes undissolved Hf particles, delta ferrite grains and cellular sub-grain boundaries that can hinder defect motion.

Influence of proton irradiation on the magnetic properties of two-dimensional Ni(II) molecular magnet

The influence of 1.9 MeV proton irradiation on structural and magnetic properties has been explored in the two-dimensional (2D) NiSO4(1,3-phenylenediamine)2 coordination ferrimagnet. The X-ray powder diffraction and IR spectroscopy revealed that the octahedrons with Ni ion in the center remain unchanged regardless of the fluence a sample received. In contrast, proton irradiation greatly influences the hydrogen bonds in the flexible parts in which the 1,3-phenylenediamine is involved. Dc magnetic measurements revealed that several magnetic properties were modified with proton irradiation. The isothermal magnetization measured at T = 2.0 K varied with the proton dose, achieving a 50% increase in magnetization in the highest measured field µ0Hdc = 7 T or a 25% decrease in remanence. The most significant change was observed for the coercive field, which was reduced by 90% compared to the non-irradiated sample. The observed results are accounted for the increased freedom of magnetic moments rotation and the modification of intralayer exchange couplings.

15 MeV proton damage in NiO/β-Ga2O3 vertical rectifiers

15 MeV proton irradiation of vertical geometry NiO/β-Ga2O3 heterojunction rectifiers produced reductions in reverse breakdown voltage from 4.3 kV to 3.7 kV for a fluence of 1013ions·cm−2 and 1.93 kV for 1014 ions·cm−2. The forward current density was also decreased by 1–2 orders of magnitude under these conditions, with associated increase in on-state resistance R ON. These changes are due to a reduction in carrier density and mobility in the drift region. The reverse leakage current increased by a factor of ∼2 for the higher fluence. Subsequent annealing up to 400 °C further increased reverse leakage due to deterioration of the contacts, but the initial carrier density of 2.2 × 1016 cm−3 was almost fully restored by this annealing in the lower fluence samples and by more than 50% in the 1014 cm−2 irradiated devices. Carrier removal rates in the Ga2O3 were in the range 190–1200 for the fluence range employed, similar to Schottky rectifiers without the NiO.

Thermal diffusivity, microstructure and nanohardness of laser-welded proton-irradiated Eurofer97

Eurofer97 steel, a candidate structural material for future fusion reactors, was examined following 1.9 MeV proton-irradiation up to 0.91(5) dpa at 450 ∘C with and without a prior post-weld heat-treatment at 760 ∘C for 4 hours in a laser-welded state. A nanoindentation study found a pile-up-corrected nanohardness of 4.0(4) GPa in the as-welded fusion zone, decreasing to 2.1(3) GPa in the parent material. Irradiation temperature and post-weld heat treatment were both found to have a recovery effect on weld hardness, with the latter being entire. Proton-irradiation damage was not found to contribute to nanohardness at the temperature investigated. X-ray diffraction analysis found increased 1-dimensional dislocation density in the as-welded fusion zone, diminishing to 3(2) – 19.2(1.4)×1014 cm−2 in the parent material, dependent on irradiation and heat-treatment. Transient grating spectroscopy of Eurofer97 was attempted, finding a systematic underestimation of thermal diffusivity of average 15.6% from room-temperature to 600 ∘C when compared to laser flash analysis. Transient grating spectroscopy was, nevertheless, applied determining a room-temperature thermal diffusivity of 7.8(3) mm2 s−1 in the parent material and 6.7(4) mm2 s−1 in the as-welded fusion zone. Irradiation at 450 ∘C alleviated this difference in thermal diffusivity; recovery of weld-induced changes was observed up to 20% in the fusion zone due to irradiation conditions, distinct from temperature effects alone. Such results bode well for Eurofer97's application in fusion reactors, where welding will be essential. Thermal diffusivity has also been mapped at a fine scale across a heterogeneous structure, a technique applicable widely outside the realm of radiation materials science.

Irradiation damage and corrosion performance of proton irradiated 304 L stainless steel fabricated by laser-powder bed fusion

The irradiation-induced microstructure and corrosion performance of proton irradiated 304 L stainless steel (SS) fabricated by laser powder bed fusion (LPBF) is investigated. Irradiation-induced dislocation loops are observed in both LPBF and traditionally manufactured (TM) 304 L SS following 2 MeV proton irradiation at 360 °C. A comparison analysis of the oxide scales formed on proton irradiated LPBF and TM 304 L SS is conducted along with the unirradiated counterparts. The irradiation-induced defects accelerate the corrosion by providing a rapid diffusion path to form a thicker and more porous film with a double-layer structure and herein the oxide film thickness of TM 304 L SS is approximately twice that of the LPBF 304 L SS. The unique microstructure of high dislocation densities, cellular sub-grains boundaries and dispersed nanoscale inclusions provides large amounts of interfaces in LPBF samples, which is benefit to absorb the irradiation-induced point defects. The irradiation induced fast diffusion paths and the nucleation points of oxides are thus reduced, resulting in a thinner oxide film thickness and a better corrosion resistance revealed by the more Cr enrichment of inner scale in LPBF 304 L SS.

Proton Irradiation-Induced Reliability Degradation of SiC Power MOSFET

The effect of 53 MeV proton irradiation on the reliability of silicon carbide power MOSFETs was investigated. Post-irradiation gate voltage stress was applied and early failures in time-dependent dielectric breakdown (TDDB) test were observed for irradiated devices. The applied drain voltage during irradiation affects the degradation probability observed by TDDB tests. Proton-induced single event burnouts (SEB) were observed for devices which were biased close to their maximum rated voltage. The secondary particle production as a result of primary proton interaction with the device material was simulated with the Geant4-based toolkit.

The effect of trapping sites introduced by 1 MeV proton irradiation on the reverse current recovery time in Ga2O3-based Schottky diodes

The reverse current recovery time is an important parameter of diodes, fast rectifiers and transistors which determined their high-frequency properties and area of application. Defects in the structure may sufficiency reduce the cutoff frequency and lead to overheating. The reverse recovery of the low currents in the α- and β-Ga2O3 Schottky diodes was measured and analyzed in this study. The reverse recovery time in the β-Ga2O3-based Schottky diode is limited mainly by the relaxation of the RC-circuit formed by the equivalent diode circuit and can be very low (20 nsec in this case). Irradiation can introduce some defects in the structure, which may act as deep levels and prolong the relaxation. We have demonstrated experimentally that increasing serial resistance of the circuit lead to an increase in the reverse recovery time. But we can point an additional part of relaxation that can be attributed to the emission from deep levels in the forbidden gap of the semiconductor. It is shown that prolongation increases with the reverse recovery time but saturates. In the α-Ga2O3-based structures the reverse recovery time measured after proton irradiation was 6 μsec, twice as high than it can be expected from RC-circuit relaxation time. These deep levels can be associated with interstitial oxygen atoms. The results obtained can be used to improve the technology of crystal growth to produce Schottky diodes with a high boundary frequency.

Effects of high-dose 80 MeV proton irradiation on the electroluminescent and electrical performance of InGaN light-emitting diodes

The paper reports on the degradation of InGaN/GaN Blue LED submitted to proton irradiation at 80 MeV and various fluences (4×1013 p cm−2 and 1×1014 p cm−2). After irradiation, we found a decrease in light output power and the external quantum efficiency with fluence. Photoluminescence (PL) measurements exhibited that the peak position at 400, 447 and 568 nm remained unchanged, only the peak intensity decreased. The intensity of the blue emission reduced by 75%, indicating that the active region degraded seriously; the intensity from In x Ga1-x N (x = 0.11) reduced more than two times in comparison with the blue emission, implying that proton irradiation affected In x Ga1-x N more seriously than InGaN/GaN MQWs. The degradation of LED is ascribed to the increase in the defect-related Shockley–Read–Hall recombination after 80 MeV proton irradiation with higher fluence.

Proton irradiation influence on gate-channel low-field carrier mobility of AlGaN/GaN HEMTs

AlGaN/GaN high electron mobility transistors (HEMTs) with different device sizes were prepared and exposed to 0.4 MeV proton irradiation. The low-field carrier transport characteristics of the gate channel are obtained from the capacitance-voltage curves and current-voltage curves. For the device with a longer gate-drain distance (30 μm), after 0.4 MeV proton irradiation, the gate-channel low-field carrier mobility increases by 14.3% on average. For the device with a shorter gate-drain distance (15 μm), the carrier mobility decreases by 13.4% on average after proton irradiation. This phenomenon is studied with regard to the polarization scattering effect. It is found that the polarization distribution in the AlGaN/GaN HEMTs changes after proton irradiation and different gate-drain distances correspond to different polarization distributions.