High-energy Proton Irradiation Research Articles

(Invited) Β-Ga2O3 Traps: Materials to Devices

Traps in β-Ga2O3 keep devices, such as power transistors, photodetectors, and diodes, from working ideally. This manifests itself as short-term (ns to ms time scales) to longer term (day to week long) instabilities in terminal characteristics including dynamic on-resistance and threshold voltage and as increased leakage currents that degrade breakdown voltage and noise equivalent power. Using both conventional deep level transient and optical spectroscopies (DLTS/DLOS) and direct, quantitative defect spectroscopy on transistors namely constant drain current DLTS (CID-DLTS), the trap energies and concentrations in test structures and metal-semiconductor field effect transistors (MESFETs) are quantified and compared with the instabilities in the MESFET threshold voltage and dynamic on-resistance are correlated showing which traps matter in these MESFETs. A critical step in defect spectroscopy is to identify the sources of defects to enable strategies to eliminate the defects or bring them down to tolerable levels. Our group and the community have made great strides in beginning to identify the defects throughout the bandgap. Using high energy proton and neutron irradiation to create native defects and controlled studies with Fe, the two primary defects that cause threshold voltage instability in MESFETs will be discussed along with mitigation strategies.

Effect of high energy (15 MeV) proton irradiation on vertical power 4H-SiC MOSFETs

The effect of irradiation with 15 MeV protons on the electrical properties of high-power vertical 4H-SiC MOSFETs of 1.2 kV class has been studied experimentally with doses in the range 0 ≤ Φ ≤ 1014 cm−2. Dose Φcr, signifying the complete degradation of the device, corresponds to the condition Φcr ≈ n0/ηe (ηe is the electron removal rate and n0 is the electron concentration in the unirradiated drift layer). In the devices under study, Φcr is 1014 cm−2. The effect of irradiation on the leakage current, gate-drain capacitance, transconductance, and field mobility was examined.

Effects of proton radiation on field limiting ring edge terminations in 4H–SiC junction barrier Schottky diodes

In this study, the effects of high-energy proton radiation on the effectiveness of edge terminations using field limiting rings (FLRs) in 4H–SiC junction barrier Schottky (JBS) diodes were examined in detail. The devices were irradiated using 5-MeV protons at fluences ranging from 5× 1012 cm−2 to 5× 1014 cm−2. Further, the reverse breakdown performances of the investigated devices were measured both before and after irradiation. Proton irradiation initially decreased the breakdown voltage (BV); subsequently, the BV was increased as the proton fluence increased. At a fluence of 5× 1013 cm−2, the BV was reduced by approximately 18%, whereas it was reduced by approximately 5% at a higher proton fluence of 5× 1014 cm−2. The related degradation mechanism that was associated with this phenomenon was also investigated using the numerical simulations of the current-voltage ( I - V ) and capacitance-voltage ( C - V ) characteristics of the device. The main contribution to the radiation-induced changes in BV originates from the variations of charge distribution at the SiO2/4H–SiC interface and the reduction of the net carrier density in the drift region. Both the aforementioned variations affect the spread of the electric field in the FLR edge termination regions.

High-energy proton irradiation damage on two-dimensional hexagonal boron nitride.

The dielectric layer, which is an essential building block in electronic device circuitry, is subject to intrinsic or induced defects that limit its performance. Nano-layers of hexagonal boron nitride (h-BN) represent a promising dielectric layer in nano-electronics owing to its excellent electronic and thermal properties. In order to further analyze this technology, two-dimensional (2D) h-BN dielectric layers were exposed to high-energy proton irradiation at various proton energies and doses to intentionally introduce defective sites. A pristine h-BN capacitor showed typical degradation stages with a hard breakdown field of 10.3 MV cm−1, while h-BN capacitors irradiated at proton energies of 5 and 10 MeV at a dose of 1 × 1013 cm−2 showed lower hard breakdown fields of 1.6 and 8.3 MV cm−1, respectively. Higher leakage currents were observed under higher proton doses at 5 × 1013 cm−2, resulting in lower breakdown fields. The degradation stages of proton-irradiated h-BN are similar to those of defective silicon dioxide. The degradation of the h-BN dielectric after proton irradiation is attributed to Frenkel defects created by the high-energy protons, as indicated by the molecular dynamics simulation. Understanding the defect-induced degradation mechanism of h-BN nano-layers can improve their reliability, paving the way to the implementation of 2D h-BN in advanced micro- and nano-electronics.

Effects of high-energy proton irradiation on separate absorption and multiplication GaN avalanche photodiode

The effect of high-energy proton irradiation on GaN-based ultraviolet avalanche photodiodes (APDs) is investigated. The dark current of the GaN APD is calculated as a function of the proton energy and proton fluences. By considering the diffusion, generation–recombination, local hopping conductivity, band-to-band tunneling, and trap-assisted tunneling currents, we found that the dark current increases as the proton fluence increases, but decreases with increasing proton energy.

Modelling of proton irradiated GaN-based high-power white light-emitting diodes

We report the effects of high-energy (23 GeV) proton irradiation at large fluences on packaged high-power GaN-based white light-emitting diodes with YAG:Ce phosphors. From optical and electrical measurements, we assume that proton irradiation degrades only the GaN LED die up to fluences of at least 2 × 1014 p/cm2, and we demonstrate that it produces nonradiative recombination centres which increase the leakage current and diminish the carrier density in the quantum wells and hence the output optical power. We also propose for the first time a model correlating optical and electrical degradation induced by radiation.

Combined Treatment Modalities for High-Energy Proton Irradiation: Exploiting Specific DNA Repair Dependencies.

DNA repair deficiencies and genome instability are common features and hallmarks of cancer and are ubiquitously found in the full spectrum of malignant diseases. Heritable DNA repair deficiencies, for example, due to BRCA1 and BRCA2 mutations, and subsequent loss of heterozygosity in mammary, ovarian, and prostate carcinoma, are risk factors for the early development of cancer. Despite their detrimental role in tumorigenesis, these deficiencies also provide novel opportunities for treatment options. Current and future pharmacologic approaches in medical oncology rely on the exploitation of such genetically defined, tumor-specific Achilles' heels and integrate the genetic background of a tumor into the treatment strategy. For example, homologous recombination-corrupted, BRCA1/2-mutated tumors are becoming hypersensitive to inhibitors of an additional DNA-damage-repair mechanism and are successfully treated with respective molecular targeting agents such as PARP1 inhibitors. Patient stratification in radiation oncology today is primarily based on clinical parameters and uses highly sophisticated diagnostic imaging for treatment planning on the individual level. Radiation oncology only minimally takes the genetic makeup of tumors into account, and little attention has been given to the fact that the different modalities of ionizing radiation, such as photon and proton irradiation, may also induce differential damages and biological processes, which might again be influenced by the genetic makeup and mutational status of the tumor. However, radiation oncology is nowadays challenged to understand subtle differences induced by the different qualities of ionizing radiation, and to efficiently exploit and to integrate these differential responses in a personalized treatment approach alone and as part of combined treatment modalities with pharmacologic agents. Here we will review recent insights on the differential DNA damage responses to photon and proton irradiation and discuss their implications for combined treatment modalities with chemotherapeutical agents and small molecular targeting compounds.

Proton-Induced Conductivity Enhancement in AlGaN/GaN HEMT Devices

We investigated the influence of proton irradiation on the AlGaN/GaN high-electron-mobility transistor (HEMT) devices. Unlike previous studies on the degradation behavior upon proton irradiation, we observed improvements in their electrical conductivity and carrier concentration of up to 25% for the optimal condition. As we increased the proton dose, the carrier concentration and the mobility showed a gradual increase and decrease, respectively. From the photoluminescence measurements, we observed a reduction in the near-band-edge peak of GaN (~ 366 nm), which correlate on the observed electrical properties. However, neither the Raman nor the X-ray diffraction analysis showed any changes, implying a negligible influence of protons on the crystal structures. We demonstrated that high-energy proton irradiation could be utilized to modify the transport properties of HEMT devices without damaging their crystal structures.

Effects of high-energy proton irradiation on the superconducting properties of Fe(Se,Te) thin films

In this paper we explore the effects of 3.5 MeV proton irradiation on Fe(Se,Te) thin films grown on CaF2. In particular, we carry out an experimental investigation with different irradiation fluences up to 7.30 · 1016 cm−2 and different proton implantation depths, in order to clarify whether and to what extent the critical current is enhanced or suppressed, what are the effects of irradiation on the critical temperature, resistivity, and critical magnetic fields, and finally what is the role played by the substrate in this context. We find that the effect of irradiation on superconducting properties is generally small compared to the case of other iron-based superconductors. The irradiation effect is more evident on the critical current density Jc, while it is minor on the transition temperature Tc, normal state resistivity ρ, and on the upper critical field Hc2 up to the highest fluences explored in this work. In more detail, our analysis shows that when protons implant in the substrate far from the superconducting film, the critical current can be enhanced up to 50% of the pristine value at 7 T and 12 K; meanwhile, there is no appreciable effect on critical temperature and critical fields together with a slight decrease in resistivity. On the contrary, when the implantation layer is closer to the film–substrate interface, both critical current and temperature show a decrease accompanied by an enhancement of the resistivity and lattice strain. This result evidences that possible modifications induced by irradiation in the substrate may affect the superconducting properties of the film via lattice strain. The robustness of the Fe(Se,Te) system to irradiation-induced damage makes it a promising compound for the fabrication of magnets in high-energy accelerators.

CIGS Solar Cells for Space Applications: Numerical Simulation of the Effect of Traps Created by High-Energy Electron and Proton Irradiation on the Performance of Solar Cells

Numerical simulation is carried out using the Silvaco ATLAS software to predict the effect of 1-MeV electron and 4-MeV proton irradiation on the performance of a Cu(In, Ga)Se2 (CIGS) solar cell that operates under the air mass zero spectrum (AM0). As a consequence of irradiation, two types of traps are induced including the donor- and acceptor-type traps. Only one of them (the donor-type trap) is found responsible for the degradation of the open-circuit voltage (VOC), fill factor (FF) and efficiency (η), while the short circuit current (JSC) remains essentially unaffected. The modelling simulation validity is verified by comparison with the experimental data. This article shows that CIGS solar cells are suited for space applications.

Study of proton radiation effect to row hammer fault in DDR4 SDRAMs

This paper shares the effects of row hammer fault through high-energy proton radiation. The significance of row hammer fault is highlighted in terms of two different technologies in DDR4 SDRAM.Row hammer stress prevents nearby storage cells from maintaining storage data within the retention time of 64-ms. The stress is worsened by the radiation damage in silicon due to the high-energy particles.Proton-based radiation damage tests were performed with DDR4 SDRAM components from two different technologies. Experiment results showed that after proton irradiation, the number of bit errors caused by the row hammering test increased about 41% and 66% in technologies 2x-nm and 2y-nm, respectively. With 2y-nm technology, bit errors started to appear from 5K Number of Hammering (NHMR)—the equivalent of 500-μs retention time. For 2y-nm components, more than 90% of failed words had multiple failed cells, which could not be corrected by Single Error Correction and Double Error Detection (SEC-DED) codes.

A study of GeV proton microprobe lens system designs with normal magnetic quadrupole

Abstract High energy proton irradiation has many applications to the study of radiation effects in semiconductor devices, biological tissues, proton tomography and space science. Many applications could be extended and enhanced by use of a high energy proton microprobe. However the design of a GeV proton microprobe must address significant challenges including beam collimation that minimizes ion scattering and the probe forming lens system for ions of high rigidity. Here we address the probe forming lens system design subject to several practical constraints including the use of non-superconducting normal magnetic quadrupole lenses, the ability to focus 1–5 GeV protons into 5 µm diameter microprobes and compatibility with the beam parameters of GeV proton accelerators. We show that 2, 3 and 4 lens systems of lenses with effective lengths up to 0.63 m can be employed for this purpose with a demagnification up to 58 and investigate the probe size limitations from beam brightness, lens aberrations and machining precision.

Stability of the tungsten diselenide and silicon carbide heterostructure against high energy proton exposure

Single layers of tungsten diselenide (WSe2) can be used to construct ultra-thin, high-performance electronics. Additionally, there has been considerable progress in controlled and direct growth of single layers on various substrates. Based on these results, high-quality WSe2-based devices that approach the limit of physical thickness are now possible. Such devices could be useful for space applications, but understanding how high-energy radiation impacts the properties of WSe2 and the WSe2/substrate interface has been lacking. In this work, we compare the stability against high energy proton radiation of WSe2 and silicon carbide (SiC) heterostructures generated by mechanical exfoliation of WSe2 flakes and by direct growth of WSe2 via metal-organic chemical vapor deposition (MOCVD). These two techniques produce WSe2/SiC heterostructures with distinct differences due to interface states generated during the MOCVD growth process. This difference carries over to differences in band alignment from interface states and the ultra-thin nature of the MOCVD-grown material. Both heterostructures are not susceptible to proton-induced charging up to a dose of 1016 protons/cm2, as measured via shifts in the binding energy of core shell electrons and a decrease in the valence band offset. Furthermore, the MOCVD-grown material is less affected by the proton exposure due to its ultra-thin nature and a greater interaction with the substrate. These combined effects show that the directly grown material is suitable for multi-year use in space, provided that high quality devices can be fabricated from it.

Radiometric evaluation of diglycolamide resins for the chromatographic separation of actinium from fission product lanthanides

Actinium-225 is a potential Targeted Alpha Therapy (TAT) isotope. It can be generated with high energy (≥ 100MeV) proton irradiation of thorium targets. The main challenge in the chemical recovery of 225Ac lies in the separation from thorium and many fission by-products most importantly radiolanthanides. We recently developed a separation strategy based on a combination of cation exchange and extraction chromatography to isolate and purify 225Ac. In this study, actinium and lanthanide equilibrium distribution coefficients and column elution behavior for both TODGA (N,N,N′,N′-tetra-n-octyldiglycolamide) and TEHDGA (N,N,N′,N′-tetrakis-2-ethylhexyldiglycolamide) were determined. Density functional theory (DFT) calculations were performed and were in agreement with experimental observations providing the foundation for understanding of the selectivity for Ac and lanthanides on different DGA (diglycolamide) based resins. The results of Gibbs energy (ΔGaq) calculations confirm significantly higher selectivity of DGA based resins for LnIII over AcIII in the presence of nitrate. DFT calculations and experimental results reveal that Ac chemistry cannot be predicted from lanthanide behavior under comparable circumstances.

The effects of high-energy proton irradiation on the electrical characteristics of Au/Ni/4H-SiC Schottky barrier diodes

Au/Ni (20:80) Schottky barrier diodes (SBDs) were resistively evaporated on nitrogen-doped n–type 4H-SiC. Current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the SDBs were investigated before and after bombardment with 1.8MeV proton irradiation at a fluence of 2.0×1012cm–2. The measurements were carried out in the temperature range 40–300K in steps of 20K. Results obtained at room temperature (300K) showed highly rectifying devices before and after bombardment. It was observed that the proton irradiation induced an increase of ideality factor from 1.05 to 1.13, a decrease in Schottky barrier height from 1.40 to 1.22eV, an increase in series resistance from 10 to 66 Ω and a noticeable increase of the saturation current from 3.0×10–21 to 6.8×10–17A. The increase in saturation current after proton irradiation was attributed to the presence of interfacial states created by irradiation-induced defects. Thermionic emission dominated the I-V characteristics in the temperature range 120–300K but the I-V characteristics deviated from thermionic emission theory at temperatures below 120K for devices both before and after irradiation. The variation of the SBDs characteristics with temperature was attributed to the presence of lateral inhomogeneities of the SBH. Modified Richardson constants were determined from a Gaussian distribution of barrier heights to be 133 and 165Acm–2K–2 before and after irradiation, respectively.

Atom redistribution and multilayer structure in NiTi shape memory alloy induced by high energy proton irradiation

The element distribution and surface microstructure in NiTi shape memory alloys exposed to 3MeV proton irradiation were investigated. Redistribution of the alloying element and a clearly visible multilayer structure consisting of three layers were observed on the surface of NiTi shape memory alloys after proton irradiation. The outermost layer consists primarily of a columnar-like TiH2 phase with a tetragonal structure, and the internal layer is primarily comprised of a bcc austenite phase. In addition, the Ti2Ni phase, with an fcc structure, serves as the transition layer between the outermost and internal layer. The above-mentioned phenomenon is attributed to the preferential sputtering of high energy protons and segregation induced by irradiation.

Radiation-Induced Defects in Si after High Dose Proton Irradiation

Experiments on investigation of the radiation defects produced as a result of high energy proton irradiation of single crystal Si wafers are carried out. Parameters of the proton irradiation facility are presented. It is shown that the most efficient radiation defect formation correlates with the position of the Bragg peak of ionization losses. LT spectra were measured just after irradiation and then after keeping Si samples during 3 months of at room T. We did not observe any variation of the number density of the defects, except for the 7th wafer, where most part of protons was stopped. An efficient annealing of the vacancy-type defects starts at temperatures slightly lower than 100 °C (during 10 min). Annealing at about 700 °C leads to recovering of the monoexponrntial shape of the LT spectra.

Radiation‐Hard and Ultralightweight Polycrystalline Cadmium Telluride Thin‐Film Solar Cells for Space Applications

AbstractAchieving high‐specific‐power and radiation hardness of solar cells is of great importance to perform tasks and achieve duration in space. Therefore, we investigated the proton irradiation resistance of ultralightweight CdS/CdTe thin film solar cells having high specific power values. High‐energy proton beams (15 MeV) with doses ranging from 1×1012 to 1×1015 cm−2 were used, equivalent to more than 2000 years in low Earth orbit. Although 70 % decrease in cell conversion efficiency was observed after proton irradiation with dose of 1×1015 cm−2, it still maintained the photovoltaic performance. The specific power of the fabricated cell decreased from 358 W kg−1 to 109 W kg−1 after proton irradiation (dose=1×1015 cm−2), which is still comparable to specific powers of other types of solar cells. Our work indicated that reduction of short circuit current is a major factor of deterioration of the cell performance under the high energy proton irradiation. This work revealed that our lightweight CdS/CdTe solar cells have significant potential for the use in space applications: reduction of launch cost by achieving high specific power and assurance of durability over prolonged space missions.

Radiation Hardness and Self-Healing of Perovskite Solar Cells.

The radiation hardness of CH3 NH3 PbI3 -based solar cells is evaluated from in situ measurements during high-energy proton irradiation. These organic-inorganic perovskites exhibit radiation hardness and withstand proton doses that exceed the damage threshold of crystalline silicon by almost 3 orders of magnitude. Moreover, after termination of the proton irradiation, a self-healing process of the solar cells commences.

Effects of 3.5 MeV proton irradiation on pure zirconium

The effects of high energy proton irradiation on pure zirconium were investigated in this study. The annealed Zr specimens (50 mm × 3 mm × 0.8 mm) were irradiated by 3.5 MeV hydrogen ions with dose ranges from 1×1013 to 1 × 1015 ions/cm2 at 335 K. The range of the proton beam penetration was measured to be 68-70 μm, depending on the surface, which is in good agreement with the SRIM simulation results. X-ray diffractometer analysis revealed that the peak intensity of the basal plane increased and the position of the peak shifted due to the proton irradiation. Field emission scanning electron microscopy results showed that with increasing irradiation dose hydrogen micro-bubbles formed, concentrated, interconnected, and eventually burst due to the excessive hydrogen pressure inside, causing surface-crack development. Measured yield and ultimate tensile strength seemed to be insignificantly affected by the proton irradiation.