MeV Alpha Particle Irradiation Research Articles

Temperature dependence of cathodoluminescence emission in irradiated Si-doped β-Ga2O3

Temperature dependent continuous and time-resolved cathodoluminescence measurements were employed to understand the luminescence from Si-doped β-Ga2O3 prior to irradiation and after 10 MeV proton and 18 MeV alpha-particle irradiation. The shape and location of the luminescence components [ultraviolet luminescence (UVL′) at 3.63 eV, UVL at 3.3 eV, and blue-luminescence at 2.96 eV] obtained from Gaussian decomposition did not change in either width or peak location, indicating that new radiation-induced trap-levels were non-radiative in nature between the 4.5 and 310 K temperature range. Activation energies, associated with thermal quenching of UVL′ and UVL bands, show temperature dependence, suggesting ionization of shallow Si-donors and a thermally activated non-radiative process.

Improved performance of SiC radiation detector based on metal–insulator–semiconductor structures

SiC is a typical wide bandgap semiconductor that has demonstrated potential applications in radiation detection and imaging, but its performance must be improved from both a material quality and device design standpoint. In this study, based on a theoretical analysis, we found that it is possible to improve the performance of SiC radiation detectors by changing the device structure from a metal/semiconductor to a metal/insulator/semiconductor design and fabricate and evaluate corresponding devices with α particle radiation detection. We experimentally confirmed that introducing an SiO2 dielectric layer can effectively improve the energy resolution of detectors, so the effect of the dielectric layer thickness on detectors’ performance was further investigated and clarified. We demonstrated that a device with a 100 nm SiO2 dielectric layer on a 15μm SiC epitaxial layer achieved the best energy resolution of 0.55% @-40 V under 5.48 MeV alpha particle irradiation. This study provides further insight to accelerate commercial applications of SiC radiation detectors.

Effect of alpha-particle irradiation dose on SiNx/AlGaN/GaN metal–insulator semiconductor high electron mobility transistors

The effects of 18 MeV alpha particle irradiation dose on the electrical properties of SiNx/AlGaN/GaN metal insulator semiconductor high electron mobility transistors (MISHEMTs) using in situ grown silicon nitride as the gate dielectric were investigated. The MISHEMT devices were irradiated with alpha particles at doses of 1 × 1012 or 1 × 1013 cm−2 at a fixed energy of 18 MeV. Device performance degradation was more prominent for the irradiated samples under high frequency operation. At a frequency of 100 kHz and gate voltage pulsed from −6 to 3 V, the saturation drain current reduction was 32% and 41% after alpha irradiation doses of 1 × 1012 and 1 × 1013 cm−2, respectively. The drain current reduction at 100 kHz also depended on the duty cycle. At higher duty cycles, the drain current reduction was less severe. The calculated carrier removal rates were in the range of 2062–2175 cm−1 for the alpha doses studied. The results demonstrate the capability of AlGaN/GaN MISHEMTs in environments where resilience to radiation is required.

Effect of Alpha-Particle Irradiation on InGaP/GaAs/Ge Triple-Junction Solar Cells.

InGaP/GaAs/Ge triple-junction solar cells were irradiated with 5.1 MeV alpha particles with different fluences. The degradations of the optical and electrical properties of InGaP/GaAs/Ge solar cells were described in terms of the variation in the short-circuit current (Isc), the open-circuit voltage (Voc), the maximum power (Pmax), the spectral response (SR), and the photoluminescence (PL) versus the 5.1 MeV alpha-particle fluences. The degradation modeling of the Isc and Voc under 1 MeV, 3 MeV, and 5.1 MeV alpha-particle irradiation was performed by calculating the introduction rate of non-radiative recombination centers, and the minority-carrier capture cross section, and the results were in good agreement with experimental data. For comparison, the degradations of the Isc and Voc were presented under 1 MeV and 3 MeV proton irradiation.

Eighteen mega-electron-volt alpha-particle damage in homoepitaxial β-Ga2O3 Schottky rectifiers

Homoepitaxial Ga2O3 rectifiers with vertical geometry were subject to 18 MeV alpha particle irradiation at fluences of 1012–1013 cm−2, simulating space radiation exposure. The range of these particles (∼80 μm) is much greater than the drift layer thickness in the structures (∼7 μm). The carrier removal rates were in the range of 406–728 cm−1 for these conditions. These values are factors of 2–3 higher than for high energy (10 MeV) protons and 2 orders of magnitude higher than for 1.5 MeV electron irradiation of the same material. The on-state resistance of the rectifiers is more degraded by alpha particle irradiation than either ideality factor or barrier height. The reverse breakdown voltage of the rectifiers increases with alpha particle dose as carriers in the drift region are removed by trapping into traps created by the radiation damage. The on/off ratio of the rectifiers was severely degraded by alpha particle-induced damage, but the reverse recovery characteristics were unaffected even by the highest dose, with values around ∼20 ns.

Alpha-particle irradiation effects on uranium-bearing Gd2Zr2O7 ceramics for nuclear waste forms

It is necessary to study the self-irradiation effects of nuclear waste forms under α-decay in the long term storage. In the present work, accelerated irradiation experiments were performed on (Gd1-4xU2x)2(Zr1-xUx)2O7 (x=0, 0.10, 0.14) samples using 0.5MeV alpha-particle irradiation at fluences ranging from 1×1014 to 1×1017ions/cm2 at room temperature. Irradiation induced microstructural evolution was examined by grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy and Field-emission scanning electron microscopy (FESEM). The results show that the main crystal structure is kept, however, weaker structural ordering is leaded as a result of intensified irradiation. And the radiation resistance is enhanced by the growing uranium content in the discussed range. Moreover, the irradiation effects as a function of depth have been discussed. Raman spectra reveal that the vibration intensity of atomic bonds are changed due to increased irradiation. In addition, the microtopography and element distribution have been kept after irradiation.

Luminescence imaging of water during alpha particle irradiation

The luminescence imaging of water using the alpha particle irradiation of several MeV energy range is thought to be impossible because this alpha particle energy is far below the Cerenkov-light threshold and the secondary electrons produced in this energy range do not emit Cerenkov-light. Contrary to this consensus, we found that the luminescence imaging of water was possible with 5.5MeV alpha particle irradiation. We placed a 2MBq of 241Am alpha source in water, and luminescence images of the source were conducted with a high-sensitivity, cooled charge-coupled device (CCD) camera. We also carried out such imaging of the alpha source in three different conditions to compare the photon productions with that of water, in air, with a plastic scintillator, and an acrylic plate. The luminescence imaging of water was observed from 10 to 20s acquisition, and the intensity was linearly increased with time. The intensity of the luminescence with the alpha irradiation of water was 0.05% of that with the plastic scintillator, 4% with air, and 15% with the acrylic plate. The resolution of the luminescence image of water was better than 0.25mm FWHM. Alpha particles of 5.5MeV energy emit luminescence in water. Although the intensity of the luminescence was smaller than that in air, it was clearly observable. The luminescence of water with alpha particles would be a new method for alpha particle detection and distribution measurements in water.

Response of Ni/4H-SiC Schottky barrier diodes to alpha-particle irradiation at different fluences

Irradiation experiments have been carried out on 1.9×1016cm−3 nitrogen-doped 4H-SiC at room temperature using 5.4MeV alpha-particle irradiation over a fluence ranges from 2.6×1010 to 9.2×1011cm−2. Current–voltage (I–V), capacitance–voltage (C–V) and deep level transient spectroscopy (DLTS) measurements have been carried out to study the change in characteristics of the devices and free carrier removal rate due to alpha-particle irradiation, respectively. As radiation fluence increases, the ideality factors increased from 1.20 to 1.85 but the Schottky barrier height (SBHI–V) decreased from 1.47 to 1.34eV. Free carrier concentration, Nd decreased with increasing fluence from 1.7×1016 to 1.1×1016cm−2 at approximately 0.70μm depth. The reduction in Nd shows that defects were induced during the irradiation and have effect on compensating the free carrier. The free carrier removal rate was estimated to be 6480±70cm−1. Alpha-particle irradiation introduced two electron traps (E0.39 and E0.62), with activation energies of 0.39±0.03eV and 0.62±0.08eV, respectively. The E0.39 as attribute related to silicon or carbon vacancy, while the E0.62 has the attribute of Z1/Z2.

Effects of 5.4 MeV alpha-particle irradiation on the electrical properties of nickel Schottky diodes on 4H–SiC

Current–voltage, capacitance–voltage and conventional deep level transient spectroscopy at temperature ranges from 40 to 300K have been employed to study the influence of alpha-particle irradiation from an 241Am source on Ni/4H–SiC Schottky contacts. The nickel Schottky barrier diodes were resistively evaporated on n-type 4H–SiC samples of doping density of 7.1×1015cm−3. It was observed that radiation damage caused an increase in ideality factors of the samples from 1.04 to 1.07, an increase in Schottky barrier height from 1.25 to 1.31eV, an increase in series resistance from 48 to 270Ω but a decrease in saturation current density from 55 to 9×10−12Am−2 from I–V plots at 300K. The free carrier concentration of the sample decreased slightly after irradiation. Conventional DLTS showed peaks due to four deep levels for as-grown and five deep levels after irradiation. The Richardson constant, as determined from a modified Richardson plot assuming a Gaussian distribution of barrier heights for the as-grown and irradiated samples were 133 and 151Acm−2K−2, respectively. These values are similar to literature values.

Performance of Monocrystalline Diamond Radiation Detectors Fabricated Using TiW, Cr/Au and a Novel Ohmic DLC/Pt/Au Electrical Contact

We investigated the performance of synthetic high purity monocrystalline diamond radiation detectors fabricated with TiW, Cr/Au and a novel metallization technique utilising diamond-like carbon tunnelling junction and Pt/Au as electrical contacts. The investigation was carried out under irradiation with 60Co gamma-rays, 90Sr electrons and 241Am alpha-particles. The experimental results with respect to I-V dark current levels, irradiation photocurrent, signal-to-noise ratio and time response have been compared and discussed. Results show an ohmic behaviour of the DLC/Pt/Au contact, a charge collection efficiency of 100% at an applied electric field of 0.377 V/ mum for all electrical contacts (under 90Sr electrons irradiation) at a correspondent dark current value of less than a picoAmpere. The single crystal CVD DLC/Pt/Au diamond radiation detector reported here shows spectroscopic energy resolution of 1.1% at an applied voltage of +450 volts (0.9 V/mum) under 5.5 MeV alpha particle irradiation. No dasiamemorypsila or dasiapumpingpsila effect was observed for the DLC/Pt/Au contact at positive bias; the signal was also stable (fluctuations below 0.5%) and reproducible under 60Co irradiation, with a signal-to-noise ratio > 10000:1 and a linearity in the dose rate response.

Alpha particle radiation effects in RF MEMS capacitive switches

The paper investigates the effect of 5 MeV alpha particle irradiation in RF MEMS capacitive switches with silicon nitride dielectric film. The investigation included MIM capacitors in order to obtain a better insight on the irradiation introduced defects in the dielectric film. The assessment employed the thermally stimulated depolarization currents method for MIM capacitors and the capacitance–voltage characteristic for MEMS switches. Asymmetric charging was monitored in MIM capacitors due different contact electrodes and injected charge interactions.

DNA DSB induced in human cells by charged particles and gamma rays: Experimental results and theoretical approaches

Purpose:To quantify the role played by radiation track structure and background fragments in modulating DNA fragmentation in human cells exposed to γ-rays and light ions.Materials and methods: Human fibroblasts were exposed in vitro to different doses (in the range from 40 – 200 Gy) of 60Co γ-rays and 0.84 MeV protons (Linear Energy Transfer, LET, in tissue 28.5 keV/μm). The resulting DNA fragments were scored under two electrophoretic conditions, in order to optimize separation in the size ranges 0.023 – 1.0 Mbp and 1.0 – 5.7 Mbp. In parallel, DNA fragmentation was simulated both with a phenomenological approach based on the “generalized broken-stick” model, and with a mechanistic approach based on the PARTRAC (acronym of PARticle TRACk) Monte Carlo code (1.32 MeV photons were used for the simulation of 60Co γ-rays).Results: For both γ-rays and protons, the experimental dose response in the range 0.023 – 5.7 Mbp could be approximated as a straight line, the slope of which provided a yield of (5.3 ± 0.4) • 10−9 Gy−1 bp−1 for γ-rays and (7.1 ± 0.6) • 10−9 Gy−1 bp−1 for protons, leading to a Relative Biological Effectiveness (RBE) of 1.3 ± 0.2. From both theoretical analyses it appeared that, while γ-ray data were consistent with double-strand breaks (DSB) random induction, protons at low doses showed significant deviation from randomness, implying enhanced production of small fragments in the low molecular weight part of the experimental range. The theoretical analysis of fragment production was then extended to ranges where data were not available, i.e. to fragments larger than 5.7 Mbp and smaller than 23 kbp. The main outcome was that small fragments (<23 kbp) are produced almost exclusively via non-random processes, since their number is considerably higher than that produced by a random insertion of DSB. Furthermore, for protons the number of these small fragments is a significant fraction (about 20%) of the total number of fragments; these fragments remain undetected in these experiments. Calculations for 3.3 MeV alpha particle irradiation (for which no experimental data were available) were performed to further investigate the role of fragments smaller than 23 kbp; in this case, besides the non-random character of their production, their number resulted to be at least as much as half of the total number of fragments.Conclusion: Comparison between experimental data and two different theoretical approaches provided further support to the hypothesis of an important role of track structure in modulating DNA damage. According to the theoretical approaches, non-randomness of fragment production was found for proton irradiation for the smaller fragments in the experimental size range and, in a significantly larger extent, for fragments of size less than 23 kbp, both for protons and alpha particles.

The application of platinum–silicide anode layer to decrease the static and turn-off losses in high-power P-i-N diode

The platinum–silicide layer was investigated as the anode contact of a high-power P-i-N diode. The thermal stability at 700 °C was found sufficient for the purpose of Pt in-diffusion from the platinum–silicide layer into the volume. The diffusion, which was controlled using the radiation defects resulting from the 10 MeV alpha particle irradiation, represents a new local lifetime control in the float zone silicon with very low-leakage current, while keeping the benefits of traditional approaches.

The influence of high-energy alpha-particle irradiation on the spectral and defect properties of a Si photovoltaic detector

In this study the influence of 5.4 MeV alpha-particle irradiation on the performance of a Si photovoltaic detector, designed for system positioning, was investigated. The responsivity of the detector at 900 nm was reduced from for the unirradiated detector to for a detector which was irradiated with an alpha-particle fluence of . Using deep-level transient spectroscopy (DLTS) and current-voltage measurements the influence of alpha-particle irradiation on the defect and electrical properties of the detectors was monitored. The electro-optical characterization was performed using an optical characterisation test station. From this preliminary investigation it would seem that alpha-particle irradiation definitely degrades the spectral response of a system-positioning photovoltaic detector. This irradiation introduces electron and hole defects in the bandgap, which have a detrimental effect on the electrical properties (reverse leakage current, dynamic resistance and ideality factor) of the junction.

A Dlts Investigation of The Effect of Ion Mass, Fluence and Energy on the Introduction of a Higher-Order Vacancy Cluster in Noble Gas Ion Bombarded n-Si

AbstractWe have recently reported the annealing and electrical properties of three new families (N1, N2 and N3) of vacancy complexes introduced in 1 keV He-, Ne- and Ar-ion bombarded nSi. In this paper we have employed deep level transient spectroscopy to investigate the ion mass, fluence and energy dependence of the introduction of N1 -defects. We observed an increase in the intensity of Ni -defects with increasing mass of bombarding ions for a fluence of 1×1012cm−2and flux of 1×1011cm−2s−1, which we have correlated with the mass dependence of nuclear energy deposition. The ratio of the intensities of Ni-defects to VO-center, [N1]/[VO], increased by ∼5 when bombarding with Ar- compared to He-ions. Increasing the Ar-ion fluence from 1×1012cm−2to l×1014cm−2for a flux of 5×1010 cm−2s−;1increased the intensity of N1-defects by ∼20 times, while [N1]/[VO] increased by a factor ∼2.3. N1-defects were not created by 5.4 MeV alpha-particle irradiation, but were present in varying relative concentrations in 1 to 150 keV He-ion bombarded n-Si.

Minority-carrier lifetime damage coefficient of irradiated InP

Minority-carrier lifetime damage coefficients for 1 MeV electron, 3 MeV proton, and 6 MeV alpha particle irradiation of n-type (4.5×1015 and 1.3×1017 cm−3) and p-type (2.5×1017 cm−3) InP have been measured using time-resolved photoluminescence. These values are relatively insensitive to carrier type and show a slight increase with increasing carrier concentration. Evidence of comparable electron and hole capture lifetimes is found for the dominant recombination defect. The effect of 3 MeV proton and 6 MeV alpha particles relative to 1 MeV electrons is an increase in the lifetime damage coefficient by factors of about 104 and 105, respectively.

Defect characterization of n-type Si1−xGex after 1.0 kev helium-ion etching

SiGe heterostructures with their associated geometries and properties promise a novel generation of Si-based devices. Surface processing and, in particular, dry or plasma etching of semiconductors is a key technology for producing optoelectronic integrated circuits and high speed electronic devices. We have used deep-level transient spectroscopy (DLTS) in an investigation of the electronic properties of defects introduced in n-Si 1 −xGex (x = 0.00 to 0.25) during 1 keV helium-ion etching (fluence = 1 × 1012 cm²) prior to the deposition of gold Schottky barrier diodes (SBDs). Six electron defects (EHel-EHe6) were detected after this processing stage. The defects detected after etching are compared to those introduced by 5.4 MeV alpha-particle (α-) irradiation and, also, radio frequency (rf) sputter-deposition of Au SBDs on material from the same wafer. Four of the electron defects (EHel, EHe2, EHe4, and EHe6) are detected in Si. The remaining two defects (EHe3 and EHe5) are only detected in material containing germanium. It was noted that defects introduced during the He-ion etch process have the same DLTS “signatures” as defects after the sputter deposition process, but none were the same as those introduced during the α-particle irradiation. The influence of increased Ge content on DLTS peak shape and positions is also illustrated and discussed.

Surface damage on stainless steel, Ni, Cu and Mo under mev alpha particle irradiation–surface damage on stainless steel, Ni, Cu, Mo

The following kinds of materials, which are potentially useful for CTR construction, namely: the 12KH18N10T, W-4541, W-4016 and SS-304 steels, Ni, Cu and Mo have been Cyclotron irradiated with 3.0, 4.7 and 6.8 MeV He ions with the aim of investigating the energy and the dose dependence of the induced surface deformation effects (blistering and flaking). We report the experimentally determined values for the blisters average diameter and for the critical fluences inducing blistering. We describe other observed features due to irradiation, as sponge-and wave-like structures, submicronic cracks, multilayer flaking, secondary blisters and microcraters. It is discussed the potential validity of the two main categories of explanations which could describe the reported phenomena: the gas driven (gas bubble coalescence) model and the stress-induced model of blistering.

Dose Dependence of Semiconductor Material Conductivity as a Means of High Fluence Dosimetry

Dose dependences of conductivity at a temperature of 78 K for InSb and InAs single crystals under reactor fast neutron, 50 MeV proton and 80 MeV alpha particle irradiation up to a fluence of 10 17 cm -2 are considered. Special attention is given to non-trivial, but little known semi-conductor characteristics in terms of a(F) dependence at large fluences, and also to the versatility of such dependence for all semiconductors. The behaviour of semiconductor materials conductivity dependence on fluence presented here may be used for semiconductor dosemeters characteristic variation forecasting under large fluence measurements and in radiation emergency dosimetry.

Upset Events in Josephson Digital Devices under Alpha Particle Irradiation

Preliminary results on the effects of 5 MeV alpha particle irradiation on the electrical characteristics of large area (approximately 60 ?m2) Josephson Nb-amorphous Si-Nb tunnel devices indicate that these particles are effective in producing upset events when the device is operated in a switching mode. For bias currents very close to the critical current, IC, upset rates are near 0.1 per alpha. At a reduced bias current of 0.65 IC the upset rate is decreased but is still finite (0.002 per alpha). In addition, an hysteretic effect was observed for the critical current of the device under alpha irradiation. A simple heating model does not appear adequate to explain the observed upset rate as a function of bias current and the hysteretic effect.