Electric orbit raising (EOR) radiation-induced coverglass (CG) damage reduces the amount of light that reaches underlying solar cells and decreases photoconversion efficiency. This article describes the modeling, simulation, and ground-based radiation tests using Qioptiq CMG borosilicate CG for five selected EOR trajectories, and the impact on the performance of III-V multijunction (MJ) solar cells. The CG optical transmission loss reaches a maximum of similar to 20% around 350 nm. However, the spectral response of the MJ solar cells at this wavelength is minimal. The test results show a darkening related to solar cell performance degradation of up to 5% for the worst-case EOR trajectory.

Micro-concentrator photovoltaics aim to provide a boosted power efficiency and to enable higher III-V manufactoring capability for space power systems while maintaing the form factor of traditional flat plate cells. The additional glass needed for the lenslets should provide a better radiation shield then coverglass and enable more radiation sensitive cell architectures with improved efficiencies to be used. We measured the radiation degradation of 1 MeV electrons on both shallow- and rear-junction GaAs cells through a lenslet array to build a predictive model of the power remaing factor and compaired the perimeter recombination current of the two architectures. We found minimal degradation up to a 1015 e-cm-2 fluence for either architecture when shielded by the lenslet array but separately the rear-junction devices saw a 20X reduction in perimeter recombination compared to the shallow-junction devices.

About 2 MeV proton numerical calculation damage indicates that a quasiflat profile is introduced into the GaN buffer layer of high‐electron‐mobility transistor (HEMT) templates. A previous transport study of such HEMT structures showed increased breakdown voltage and reduced GaN buffer layer leakage after proton irradiation. Hyperspectral electroluminescence measurements detected the emission band in the spectral region between 700 and 800 nm. This emission is assumed to be associated with the generation of trap levels responsible for the device failure. To obtain insights into the nature of radiation‐generated traps, detailed low‐temperature photoluminescence (PL) and cathodoluminescence (CL) experiments are conducted in a set of virgin and proton‐irradiated device structure templates. Both the PL and CL spectra show large intensity variations of all emission bands, in the spectral range between 330 and 890 nm, with increasing proton dosage. This is consistent with the introduction of compensating and/or nonradiative recombination centers in the GaN buffer layer. Luminescence measurements carried out under various excitation conditions show different recombination rates for emission bands observed near 420 and 550 nm, indicating different free carrier capture rates. Spectral analysis suggests that these two emission bands have different dependences on proton irradiation dosage, consistent with different chemical natures.

Measurements are presented which show the effect of proton irradiation on the irreversibility line and critical current in Tl2 CaBa2Cu2O8 thin films. These data show that the irreversibility line is dependent on the defect structure and that the pinning energy is increased by proton irradiation. This leads to an increase in the critical current density at 60 K for the lowest radiation dose. Further irradiation reduces the critical current, even while the irreversibility line is enhanced.

We report T-2 spin coherence times for electronic states localized in Si vacancies in 4H-SiC. Our spin coherence study included two SiC samples that were irradiated with 2MeV protons at different fluences (10(13) and 10(14) cm(-2)) in order to create samples with unique defect concentrations. Using optically detected magnetic resonance and spin echo, the coherence times for each sample were measured across a range of temperatures from 8 to 295 K. All echo experiments were done at a magnetic field strength of 0.371 T and a microwave frequency of 10.49 GHz. The longest coherence times were obtained at 8 K, being 270 +/- 61 mu s for the 10(13) cm(-2) proton-irradiated sample and 104 +/- 17 mu s for the 10(14) cm(-2) sample. The coherence times for both samples displayed unusual temperature dependencies; in particular, they decreased with temperature until 60 K, then increased until 160 K, then decreased again. This increase between 60 and 160 K is tentatively attributed to a motional Jahn-Teller effect. The consistently longer lifetimes for the 10(13) cm(-2) sample suggest that a significant source of the spin dephasing can be attributed to dipole-dipole interactions between Si vacancies or with other defects produced by the proton irradiation. The lack of a simple exponential decay for our 10(14) cm(-2) sample indicates an inhomogeneous distribution of defect spins.

GaN high electron mobility transistors (HEMTs) have shown the potential to be extremely tolerant of the space radiation environment. To understand whether this radiation tolerance extends to millimeter wave GaN technology nodes, we have investigated the performance of discrete devices made with a commercial Ka-band AlGaN/GaN HEMT process after exposure to 2 MeV proton irradiation. In addition, we evaluate the large signal RF performance to enable the extraction of relevant device metrics (output power, gain, PAE) and understand how this performance compares to existing models for radiation-induced degradation of DC and pulsed I-V parameters. (c) The Author(s) 2017. Published by ECS. All rights reserved.

Gallium nitride-based high electron mobility transistors (HEMTs) represent a critical next-generation technology for RF amplifiers. In this work, we implement electroluminescence (EL) imaging to study breakdown mechanisms under high voltage stress conditions in as-fabricated and proton irradiated devices. After irradiation, an increased breakdown voltage and reduced buffer leakage was observed and attributed to the formation of a back barrier structure due to carrier type conversion in the buffer layer from the introduction of donor trap levels near the conduction band. In addition to identifying high field regions associated with device failure, the hyperspectral filter enables spectrum extraction, identifying peaks in the 700 nm–900 nm region associated with both defects and hot electrons that are contributing to device failure, but no change in signature after irradiation implying that radiation-induced defects are non-radiative. Complementary photoluminescence spectroscopy identified a reduction in free carrier density consistent with the generation of compensating trap levels, supporting the proposed model.

Radiation tolerance of AlGaN/GaN high-electron mobility transistors (HEMTs) is studied with 2-MeV protons, up to a fluence of 6 x 10(14) H+/cm(2) (about 200 times of typical Si MOSFET rating). The increase in dynamic ON-resistance (RONDYN) after radiation is observed to be much more severe than that of static ON-resistance. Radiation-induced donor-like traps located near the two-dimensional electron gas trap electrons, which is responsible for the phenomenon. Compared with the devices passivated by conventional plasma-enhanced chemical vapor deposition (PECVD) SiN, GaN HEMTs with 10 nm of in situ SiN before the PECVD SiN step demonstrate much less increase in RONDYN from 2300% to only 300%. The in situ SiN is believed to reduce the process damage by PECVD, improving radiation tolerance.

The radiation tolerance of AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on high quality, low threading dislocation density (TDD) ammonothermal GaN and hydride vapor phase epitaxy GaN substrates was studied and compared to the radiation response of devices on SiC substrates where the TDD is 10(4) times higher. Hall and transport measurements were performed as a function of 2 MeV proton fluence. The threading dislocation density had no effect on the radiation response. Comparing the results with published data reveals that almost all irradiated GaN-based HEMTs respond to radiation damage similarly regardless of differences in initial film quality, device structure, aluminum mole fraction, etc. AlGaAs/GaAs HEMTs are also shown to behave similarly but are around ten times more sensitive to radiation damage than GaN-based HEMTs. Known values of the displacement energy thresholds in GaN and GaAs are used to calculate that 36% fewer defects are created in GaN than in GaAs, which is too small to cause a 1000% difference in radiation sensitivity between GaN-and GaAs-based HEMTs. An alternative explanation is proposed in which the piezoelectric field at the AlGaN/GaN interface causes scattered carriers to be reinjected into the 2DEG channel, thereby mitigating some of the harmful radiation effects. (C) The Author(s) 2016. Published by ECS. All rights reserved.

Spintronics utilizes spin or magnetism to provide new ways to store and process information and is primarily associated with the utilization of spin polarized currents in memory and logic devices. With the end of silicon transistor technology in sight, spintronics can provide new paradigms for information processing and storage. Compared to charge based electronics, the advantages of magnetism/spin based devices are nonvolatility and ultra low power. In particular, magnetoresistive random access memories (MRAMs) are known to be “Rad Hard” [HXNV0100 64K x 16 Non-Volatile Magnetic RAM ( www.honeywell.com/aerospace ), S. Gerardin and A. Paccagnella, IEEE Trans. Nucl. Sci. 57 (6), 3016–3039 (2010), R.R. Katti, J. Lintz, L. Sundstrom, T. Marques, S. Scoppettuolo, and D. Martin, Proceedings of IEEE Radiation Effects Data Workshop, 103–105 (2009)] and are considered to be critical components for space and military systems due to their very low power consumption and nonvolatility. However, advances in the magnetic nanostructures and new materials for the scalability of MRAM and other potential applications require a re-evaluation of their radiation hardness. This review focuses mainly on recent progress in understanding the effects of irradiation on the magnetic materials and magnetic structures that are related to MRAM technology. Up to date, the most pronounced effects on the microstructures and the properties are linked to the displacement damage associated with heavy ion irradiation; however, the thermal effect is also important as it acts as an annealing process to recover the damage partially. Critical metrics for the magnetic tunnel junctions for postmortem characterizations will also be discussed. Finally, with the introduction of new perpendicular magnetic layers and the very thin MgO barrier layer in the next generation MRAM, the effects of the ionization damage shall be studied in the future.

Proton-induced damage in AlGaN/GaN HEMTs was investigated using energy-dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM), and simulated using a Monte Carlo technique. The results were correlated to electrical degradation using Hall measurements. It was determined by EDS that the interface between GaN and AlGaN in the irradiated HEMT was broadened by 2.2 nm, as estimated by the width of the Al EDS signal compared to the as-grown interface. The simulation results show a similar Al broadening effect. The extent of interfacial roughening was examined using high resolution TEM. At a 2 MeV proton fluence of 6 × 1014 H+/cm2, the electrical effects associated with the Al broadening and surface roughening include a degradation of the ON-resistance and a decrease in the electron mobility and 2DEG sheet carrier density by 28.9% and 12.1%, respectively.

Single-event transients (SETs) were investigated in Al0.3Ga0.7N/GaN high-electron-mobility transistors (HEMTs) using optical excitation via two-photon absorption and by heavy ions. The amplitudes and widths of the SETs were found to depend on a number of different factors, including bias conditions, strike location, and material quality.

Single-event transients (SETs) were investigated in Al0.3Ga0.7N/GaN high-electron-mobility transistors (HEMTs) using optical excitation via two-photon absorption and by heavy ions. The amplitudes and widths of the SETs were found to depend on a number of different factors, including bias conditions, strike location, and material quality.

We show that, as in the cuprate superconductors, the superconducting transition temperature in irradiated iron pnictides decreases linearly with increasing induced defect concentration, largely independent of the initial onset T-c or the incident particle's mass or energy. We attribute this to depairing caused by scattering of Cooper pairs out of the quasi two-dimensional FeAs planes. Published by Elsevier B.V.

Central giant cell granulomas of the jaws are typically known as being nonaggressive, non-neoplastic lesions initially termed giant cell reparative granulomas. These lesions most commonly present incidentally as a unilocular radiolucency in the mandible. However, some present with pain and perforation of the cortical bony plate. We present a case of a central giant cell granuloma referred for endodontic evaluation when the patient presented with pain, swelling, and a non-vital pulp. Radiographic evaluation showed a unilocular radiolucency associated with the root of a mandibular premolar causing spiking resorption. Further review of the patient’s radiographic history revealed the lesion was much smaller but visible at the initial visit 7 months prior to symptoms. Cone beam computed tomography (CBCT) evaluation revealed erosion of the buccal alveolar bone. Biopsy proved the lesion to be a central giant cell granuloma. As of January 2014, the patient has healed properly with no recurrence of the lesion. In our case, CBCT provided additional information leading to immediate biopsy rather than root canal therapy. Though in up to 70% of cases additional clinically relevant data is obtained, CBCT use is not routine in endodontic therapy. We review the current guidelines for CBCT use for evaluation of periapical pathology.

The response of InGaAs quantum well solar cells (QWSCs) to proton irradiation is presented. The QWSCs consisted of sixteen layers of 5 nm InGaAs QWs / 10 nm InAlGaAs barriers were embedded into the i-region of a 1.0 eV InAlGaAs solar cell, and the results were compared to a 1.0 eV InAlGaAs control solar cell. We report the results of 3 MeV proton irradiation using light J-V measurements of both of these devices. Due to the specific design of the structures in this study, QW devices were found to be less radiation tolerant than the control InAlGaAs devices. EQE measurements reveal that the diffusion length in the base layer of the junction has a significant affect on the loss in short circuit current of these devices. The quantum well structures showed a particular radiation robustness in comparison, largely due to the maintenance of the electric field at these fluences.

The degradation mechanisms of AlGaN/GaN high electron mobility transistors (HEMTs) grown on sapphire, Si, and SiC substrates, under 2 MeV proton irradiation are investigated. It was determined by electron channeling contrast imaging that the threading dislocation density of the AlGaN/GaN epitaxial layers is highest on sapphire substrates and lowest on SiC substrates. Photoluminescence spectroscopy confirmed the material quality order from worst to best to be AlGaN/GaN grown on sapphire, Si, and SiC substrates, respectively. The radiation response of sheet carrier density was not statistically different for HEMTs on each substrate, however the mobility degraded more for HEMTs with less initial dislocations (on SiC) than more defective HEMTs (on sapphire).

AlGaN/GaN high electron mobility transistors grown on Si, SiC, and sapphire substrates were exposed to 2-MeV proton irradiation in incremental fluences up to 6 × 10 14 cm -2 . The devices were characterized initially and after each irradiation by Hall and dc I-V measurements to probe the mechanisms associated with radiation-induced degradation and failure. It was determined that defects created at the AlGaN/GaN interface introduce scattering centers near the two-dimensional electron gas (2DEG), which result in degraded mobility. Additionally, charged traps in the structure serve to screen the 2DEG resulting in reduced sheet carrier density. These two effects are responsible for degraded I-V behavior, including reduced saturation current and transconductance, increased ON-resistance, and positive threshold voltage shift. Interestingly, the sample with the most pre-existing defects was the most tolerant of radiation-induced damage.

AlGaN/GaN high-electron mobility transistors (HEMTs) were exposed to 2-MeV protons irradiation, at room temperature, up to a fluence of 6 × 10 14 H + /cm 2 . Aside from degradation resulting from radiation-induced charge trapping, transmission electron microscopy and electrical measurements reveal a radiation-induced defect located at the edges of the Ni/Au Schottky gate in the proton-irradiated devices. At the edges of the Ni/Au gate, the Ni of the Ni/Au gate diffused up into the Au layer and migrated into the AlGaN barrier, leaving voids in the Ni layer at the gate edges after irradiation. These radiation-induced voids are caused by diffusion of Ni through vacancy exchange, known as the Kirkendall effect, resulting in reduced gate area and degrading the HEMT performance.