Low-energy Proton Irradiation Research Articles

Influence of electrical field on the susceptibility of gallium nitride transistors to proton irradiation

Radiation susceptibility of electronic devices is commonly studied as a function of radiation energetics and device physics. Often overlooked is the presence or magnitude of the electrical field, which we hypothesize to play an influential role in low energy radiation. Accordingly, we present a comprehensive study of low-energy proton irradiation on gallium nitride high electron mobility transistors (HEMTs), turning the transistor ON or OFF during irradiation. Commercially available GaN HEMTs were exposed to 300 keV proton irradiation at fluences varying from 3.76 × 1012 to 3.76 × 1014 cm2, and the electrical performance was evaluated in terms of forward saturation current, transconductance, and threshold voltage. The results demonstrate that the presence of an electrical field makes it more susceptible to proton irradiation. The decrease of 12.4% in forward saturation and 19% in transconductance at the lowest fluence in ON mode suggests that both carrier density and mobility are reduced after irradiation. Additionally, a positive shift in threshold voltage (0.32 V and 0.09 V in ON and OFF mode, respectively) indicates the generation of acceptor-like traps due to proton bombardment. high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy analysis reveal significant defects introduction and atom intermixing near AlGaN/GaN interfaces and within the GaN layer after the highest irradiation dose employed in this study. According to in-situ Raman spectroscopy, defects caused by irradiation can lead to a rise in self-heating and a considerable increase in (∼750 times) thermoelastic stress in the GaN layer during device operation. The findings indicate device engineering or electrical biasing protocol must be employed to compensate for radiation-induced defects formed during proton irradiation to improve device durability and reliability.

Energy-Dependent Impact of Proton Irradiation on 4H-SiC Schottky Diodes

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.

Low-intensity low-temperature analysis of perovskite solar cells for deep space applications

Perovskite solar cells (PSCs) are studied in low-intensity low-temperature (LILT) conditions before and after low energy proton irradiation to characterize device performance at deep space mission-relevant light intensities and temperatures.

Molecular level manipulation of charge density for solid-liquid TENG system by proton irradiation

With the rapid development of flexible electronics, methods for improving the performance of self-powered triboelectric nanogenerators (TENGs) have been in continuous demand. Due to its low density, and excellent physical and chemical properties, polyimide (Kapton or PI) was applied widely in space. As space materials such as spacecraft, PI will be irradiated by protons and other charged particles during the long-term service in space. In this study, we proposed a surface modification method using low-energy proton irradiation for tuning the internal chemical structure and functional groups at the molecular level and improving TENG performance. A solid-liquid dual-phase TENG using gallium–indium (Ga-In) eutectic alloy as liquid-phase friction material and PI as solid-phase friction material was successfully prepared. Systematic studies about the PI performance induced by proton irradiation parameters can bring insights into the interaction between the density of unsaturated bonds and electrification performance. The effect mechanism of proton irradiation on TENG property was elucidated. Compared with the initial state, the open-circuit voltage of the solid-liquid dual-phase TENG based on Ga-In eutectic alloy increased by about 57.4 % to 107.5 V, the short-circuit current density was 2.02 μA·cm−2, and the charge transfer density was 103.22 μC·m−2. Astonishingly, proton irradiation, which normally has adverse effects on devices, achieved a significant improvement in solid-liquid dual-phase TENG performance. High charge density is the key factor affecting the performance of TENG devices, and this study revealed a different approach for modifying the characteristics of solid-liquid dual-phase TENG. On the basis of the results of this study and through a series of possible breakthroughs in outer space and other environments, the reliable power supply by Ga-In eutectic alloy integrated TENG, under the presence of radiation, can be realized.

In-depth investigation of low-energy proton irradiation effect on the structural and photoresponse properties of ε-Ga2O3 thin films

Ga2O3 possesses an ultra-wide bandgap (∼4.9 eV) and an extremely large breakdown field strength (∼8 MV/cm), which promises extraordinary application potential in power electronics and ultraviolet optoelectronics. With the demand for highly durable devices in harsh environments such as in low earth orbit spacecraft, in-depth understanding of the particle radiation effect on the structural and performance degradation of the device is desired. In this work, we employ 150 keV low energy proton with intensity up to 5 × 1015 dose to irradiate the epitaxial ε-Ga2O3 thin films. The characterization of the structural and optical properties shows no detectable variations in lattice structure and optical transmission. In addition, with increasing irradiation dosage, a decrease of Ga3+ population and an increase of the concentration of oxygen vacancies are confirmed by X-ray photoemission spectroscopy. Photoresponse measurements further illustrate that, despite of a mild degradation in the photodetector performance, the device still shows a high photoresponsivity of 2.52 × 10-3 A/W and a large photo-to-dark current ratio over 103. Our work reveals that ε-Ga2O3 exhibits excellent radiation hardness under low-energy proton irradiation conditions and highlights the potential for operational optoelectronics in extreme environment.

Hybrid Lockstep Technique for Soft Error Mitigation

This work presents the evaluation of a new dual-core lockstep hybrid approach aimed to improve the fault tolerance in microprocessors. Our approach takes advantage of modern multicore processor resources to combine software-based lockstep with a custom hardware observer. The first is used to duplicate data and instruction flows; meanwhile, the second is in charge of the control-flow monitoring. The proposal has been implemented in a dual-core ARM microprocessor and validated with low-energy proton irradiation and emulated fault injection campaigns. The results show an improvement of one order of magnitude in the cross section of the benchmarks tested, even considering the worst case scenario.

Giant Orbital Anisotropy with Strong Spin–Orbit Coupling Established at the Pseudomorphic Interface of the Co/Pd Superlattice

Orbital anisotropy at interfaces in magnetic heterostructures has been key to pioneering spin–orbit‐related phenomena. However, modulating the interface's electronic structure to make it abnormally asymmetric has been challenging because of lack of appropriate methods. Here, the authors report that low‐energy proton irradiation achieves a strong level of inversion asymmetry and unusual strain at interfaces in [Co/Pd] superlattices through nondestructive, selective removal of oxygen from Co3O4/Pd superlattices during irradiation. Structural investigations corroborate that progressive reduction of Co3O4 into Co establishes pseudomorphic growth with sharp interfaces and atypically large tensile stress. The normal component of orbital to spin magnetic moment at the interface is the largest among those observed in layered Co systems, which is associated with giant orbital anisotropy theoretically confirmed, and resulting very large interfacial magnetic anisotropy is observed. All results attribute not only to giant orbital anisotropy but to enhanced interfacial spin–orbit coupling owing to the pseudomorphic nature at the interface. They are strongly supported by the observation of reversal of polarity of temperature‐dependent Anomalous Hall signal, a signature of Berry phase. This work suggests that establishing both giant orbital anisotropy and strong spin–orbit coupling at the interface is key to exploring spintronic devices with new functionalities.

Numerical simulation analysis of low energy proton irradiation mechanism of In x Ga1-x As (x = 0.2, 0.3, 0.53) solar cell

In this paper, we present an approach to study the electrical and spectral degradation properties of In x Ga1-x As (x = 0.2, 0.3, 0.53) solar cell under 150 keV proton irradiation based on numerical simulation. First, the structures of In x Ga1-x As solar cell were optimized by adjusting the doping concentration of base layer and modifying the thickness of base and emitter layer. The structural parameter related to providing higher conversion efficiency was figured out. Then, the degradation of electrical parameters such as short-circuit current density (Jsc ), open-circuit voltage (Voc ), maximum output power (P max), fill factor (FF), as well as the spectral response were obtained. The degradation correlation with radiation-induced defects was built to reveal the damage mechanism under 150 keV proton irradiation. This study provides constructive model of In x Ga1-x As to be applied in multi-junction solar cells, and the predicted degradation behavior could contribute to design the radiation-hardened space devices.

Ultrafast nonadiabatic dynamics of λ-DNA upon low energy proton irradiation

Direct ionizing damage and indirect secondary electron damage play important parts in the cell death under ion beam radiation. Depending on the real-time time-dependent density functional theory, we study the physical and chemical properties of the normal (α-) and mutant DNA (λ-DNA) in the process of low energy proton irradiation. The mutation of base pair causes the change in local chemical environment of DNA molecule and further changes the charge density of trajectory, proton–DNA interaction energy, force and track for moving proton, energy deposition, and the secondary electron evolution. The layered discrete charge in the intruding direction results in a spatial insensitivity of the electrons on the base pair to the energetic ion. The abnormal energy deposition for λ-DNA is ascribed to the mutation of the charge density and the nucleus–nucleus interaction potential. A more stable bond is formed between the mutant base pairs for λ-DNA, and there exists a flow of secondary electrons on the phosphate backbone under the ion beam radiation, resulting in a subsequent indirect chemical damage. These results provide an understanding for the central role of the physical states in radiation-induced cell death and a theoretical reference to improve the success rate of ion beam radiotherapy.

Effect of low energy proton and He particle irradiation on CsPbBr3 material

In this paper, the effect of proton and He particle bombardment in CsPbBr3 material was investigated by the Monte Carlo simulation including ion range, backscattering, vacancies and sputtering yield. The energies of proton and He particle varied from 50 keV to 180 keV and the particle incidence angles increased from 0o to 89.9o . The calculated results showed that with the increase of incidence energies, the range and vacancies increased, and the backscattering ions and sputtering yield reduced for proton and He particle. Meanwhile, the vacancies, backscattering ions and sputtering yield induced by He particle were much more proton at the same energy. With the increase of incidence angles, the range and vacancies were reduced, and the sputtering yield increased for proton and He particle. Also, it is obvious that the effects of He particle on CsPbBr3 material were much more serious than proton.

A New Low-Energy Proton Irradiation Facility to Unveil the Mechanistic Basis of the Proton-Boron Capture Therapy Approach

Protontherapy (PT) is a fast-growing cancer therapy modality thanks to much-improved normal tissue sparing granted by the charged particles’ inverted dose-depth profile. Protons, however, exhibit a low biological effectiveness at clinically relevant energies. To enhance PT efficacy and counteract cancer radioresistance, Proton–Boron Capture Therapy (PBCT) was recently proposed. PBCT exploits the highly DNA-damaging α-particles generated by the p + 11B→3α (pB) nuclear reaction, whose cross-section peaks for proton energies of 675 keV. Although a significant enhancement of proton biological effectiveness by PBCT has been demonstrated for high-energy proton beams, validation of the PBCT rationale using monochromatic proton beams having energy close to the reaction cross-section maximum is still lacking. To this end, we implemented a novel setup for radiobiology experiments at a 3-MV tandem accelerator; using a scattering chamber equipped with an Au foil scatterer for beam diffusion on the biological sample, uniformity in energy and fluence with uncertainties of 2% and 5%, respectively, was achieved. Human cancer cells were irradiated at this beamline for the first time with 685-keV protons. The measured enhancement in cancer cell killing due to the 11B carrier BSH was the highest among those thus far observed, thereby corroborating the mechanistic bases of PBCT.

Modification of spray-deposited CdO thin films by 1.5 MeV proton irradiation

Thin films of cadmium oxide (CdO) with different thicknesses in the range of 78–250 nm were prepared and deposited on glass substrates by using a spray pyrolysis technique. A microbeam facility (Lund Ion Beam Analysis facility) was used to irradiate the prepared CdO thin films with a 1.5 MeV proton beam for fluence in the range of 2 × 1012–2 × 1014 ions/cm2. The surface morphology of the CdO films was measured by atomic force microscopy, and it was observed that the grain size and surface roughness were increased as a function of ion fluence. A UV spectrophotometer was used to study the optical properties of the samples, and the results revealed that the absorbance and optical band gaps increased with an increase in the proton fluence and CdO film’s thickness. This work explores the possibility of CdO material modification using low-energy proton irradiation.

Radiation-hardened property of single-walled carbon nanotube film-based field-effect transistors under low-energy proton irradiation

Strong C–C bonds, nanoscale cross-section and low atomic number make single-walled carbon nanotubes (SWCNTs) a potential candidate material for integrated circuits (ICs) applied in outer space. However, very little work combines the simulation calculations with the electrical measurements of SWCNT field-effect transistors (FETs), which limits further understanding on the mechanisms of radiation effects. Here, SWCNT film-based FETs were fabricated to explore the total ionizing dose (TID) and displacement damage effect on the electrical performance under low-energy proton irradiation with different fluences up to 1 × 1015 p/cm2. Large negative shift of the threshold voltage and obvious decrease of the on-state current verified the TID effect caused in the oxide layer. The stability of the subthreshold swing and the off-state current reveals that the displacement damage caused in the CNT layer is not serious, which proves that the CNT film is radiation-hardened. Specially, according to the simulation, we found the displacement damage caused by protons is different in the source/drain contact area and channel area, leading to varying degrees of change for the contact resistance and sheet resistance. Having analyzed the simulation results and electrical measurements, we explained the low-energy proton irradiation mechanism of the CNT FETs, which is essential for the construction of radiation-hardened CNT film-based ICs for aircrafts.

Influence of low-energy proton irradiation on the effective lifetime in the space charge region of silicon n+-p junctions

The effect of low-energy proton irradiation on the pulse characteristics of silicon n+-p-p+ structures is analyzed. It is shown that irradiation with protons with an energy of 180 keV and a dose of 1015 cm−2 creates a region with an effective lifetime of 5.5·10−8 s in the space charge region of the n+-p junction. Such elements can be used to create high-speed photodiodes with an operating modulation frequency of 18 MHz.

Evolution of optical properties and molecular structure of PCBM films under proton irradiation

Low-energy proton irradiation effects on the optical properties and the molecular structure of phenyl-C61-butyric acid methyl ester (PCBM) are studied in this work. The PCBM films are irradiated by 100-keV proton beams with fluences of 5 × 1012 p/cm2, 5 × 1013 p/cm2, and 5 × 1014 p/cm2, respectively. The photoluminescence (PL) peaks of the post-irradiated PCBM films show a progressive decrease in the peak intensity as the proton fluences increase, which can be attributed to the deep defect levels induced by proton irradiation. Additionally, a slight blue-shift in the PL spectrum is also observed at a proton fluence of 5 × 1014 p/cm2. The underlying mechanism can be traced back to the lift of the lowest unoccupied molecular orbital (LUMO) level, which is caused by the attachment of methoxy radicals on ortho position of the phenyl ring in the post-irradiated PCBM structure. This work is of significance in understanding the radiation hardness and the damage mechanism of the PCBM film in radiation environments, which is essential before it is put into practical application in space.

Physico-Chemical Behavior and Thermo-Optical and Mechanical Properties of Glassy Carbon Up to 2100 K Under Low-Energy Proton and Vacuum Ultraviolet Irradiations

In the frame of mission for the Sun approach, to understand the effects of the heating of the solar corona and the acceleration of the solar winds, research was carried out to study the behavior of glassy carbon that can be used for the heat shield. The physicochemical behavior of glassy carbon from 1600 up to 2100 K with or without proton bombardment and VUV irradiation was studied together with the measurement of the thermal optical properties, the ratio of the solar absorptivity to the total hemispherical emissivity conditioning the thermal equilibrium of the heat shield. Experimental results obtained on massive glassy carbon samples are presented through mass spectrometry, mass loss rate and microstructural characterization (XRD, SEM…), mechanical and thermo-optical properties. Finally, the synergistic effect of high temperature, protons and VUV radiation has a low impact on this material.

Observation of Low-Energy Proton Direct Ionization in a 72-Layer 3-D NAND Flash Memory

Single-event upsets are observed in a 72-layer 3-D NAND flash memory operated in a single-level cell mode after low-energy proton (500 keV-1.2 MeV) and heavy-ion irradiation. The layer-by-layer error count is analyzed to visualize the stopping of low-energy protons within the memory stack, and Monte Carlo simulations are correlated with the experimental data. Direct ionization by low-energy protons is identified by 3-D data analysis and the energy dependence of device-sensitive cross section. Heavy-ion data is also presented for comparison.

Electrical Measurement of Cell-to-Cell Variation of Critical Charge in SRAM and Sensitivity to Single-Event Upsets by Low-Energy Protons

The distribution of single-event upsets (SEUs) in commercial off-the-shelf (COTS) static random access memory (SRAM) has generally been thought to be uniform in a device. However, process-induced variation within a device gives rise to variation within the cell-level electrical characteristic known as the data retention voltage ( V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> DR</sub> ). Furthermore, V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> DR</sub> has been shown to directly influence the critical charge ( Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> C</sub> ) necessary for stored data to upset. Low-energy proton irradiation of COTS SRAMs exhibits a preference toward upsetting cells with lower Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> C</sub> . An electrical procedure is presented to map relative cell critical charge values without knowledge of the underlying circuitry, allowing customized device usage. Given cell-level Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> C</sub> knowledge, a device can have its cells “screened” such that those with low Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> C</sub> are not used to store data. This work presents the results such a screening process has on the SEU per bit cross section.

Enhancement in the critical current density of BaTiO3-doped YBCO films by low-energy (60 keV) proton irradiation

Although YBa2Cu3O72212δ (YBCO) is one of the most promising superconducting materials for power applications, the fabrication of low-cost coated conductors with the high in-field performance remains challenging. Here, we report an efficient mixed-pinning landscape for enhancing the in-field performance of BaTiO3 (BTO)-doped YBCO films by low-energy (60 keV) proton irradiation. The smaller (2–4 nm), weaker but perhaps denser pinning sites have been successfully introduced by irradiation, which can form a mixed-pinning landscape with pre-doped BTO precipitates (5–15 nm), leading to the increased vortex pinning. In this case, the critical current density (J c) of YBCO films increases significantly, especially at low temperature and high magnetic field, and it increases three times near 6 T at 20 K when the irradiation dose is 1 × 1015 proton cm−2. Additionally, the c-axis length (c-parameter) of YBCO increases with the increase of irradiation dose, which indicates the decreasing oxygen content due to the excessive irradiation, thereby the reduction in critical transition temperature (T c). Employing low irradiation energy is beneficial for protons to stop inside YBCO film and thereby induces higher density defects when applying low doses. This fabrication technique is a practicable post-production solution to improve the in-field performance of nanoparticle-doped YBCO films.

Deep level transient spectroscopy investigation of ultra-wide bandgap (2̄01) and (001) β-Ga2O3

This work reports on a comprehensive examination of the electrical and thermal properties of vertical Schottky diodes fabricated on (2¯01)- and (001)-oriented samples of β-Ga2O3. The temperature-dependent current–voltage (I–V) and capacitance–voltage (C–V) data were gathered and analyzed down to 60 K. Deep level transient spectroscopy (DLTS) was used to study bulk and interface defects in the two materials from approx. 325 K down to 60 K. In the bulk (2¯01) material, an electron trap was observed at EC−0.46 eV, with a capture cross section of 1.6 × 10−14 cm2 and a lambda-corrected maximum trap density of 9.08 × 1015 cm−3. These results and others indicate that the electron trap is a strong candidate for the well-known E1 defect in β-Ga2O3 based on recent investigations. Additionally, in the (2¯01) material, the smooth modulation typical of interface states is evident at temperatures below 275 K. The (001) samples manifested what is likely the E2* electron trap at EC−0.68 eV, with a capture cross section of 1.64 × 10−15 cm2 and a lambda-corrected maximum trap density of 8.85 × 1015 cm−3. The presence of the E2* defect, in particular, is a contrast to the findings of recent DLTS investigations on β-Ga2O3, which report that E2* emerged only after low-energy proton irradiation. These results help to further map out the defect signatures found in β-Ga2O3 materials, which are of vital importance in the design and fabrication of future β-Ga2O3 devices.