Improved Radiation Hardness Research Articles

Design and Performance of an InAs Quantum Dot Scintillator with Integrated Photodetector

A new scintillation material composed of InAs quantum dots (QDs) hosted within a GaAs matrix was developed, and its performance with different types of radiation is evaluated. A methodology for designing an integrated photodetector (PD) with a low defect density and that is optically matched to the QD’s emission spectrum is introduced, utilizing an engineered epitaxial InAlGaAs metamorphic buffer layer. The photoluminescence (PL) collection efficiency of the integrated PD is examined using two-dimensional scanning laser excitation. The detector response to 5.5 MeV α-particles and 122 keV photons is presented. Yields of 13 electrons/keV for α-particles and 30–60 electrons/keV for photons were observed. The energy resolution of 12% observed with α-particles was mainly limited by noise- and geometry-related optical losses. The radiation hardness of an InAs QDs hosted within GaAs and a wider band gap AlGaAs ternary alloy was studied under a 1 MeV proton implantation up to a 1014 cm−2 dose. The integrated PL responses were compared to evaluate PL quenching due to non-radiative defects. The QDs embedded in the AlGaAs demonstrated improved radiation hardness compared to QDs in the GaAs matrix and in the InGaAs quantum wells.

Enhancing plastic scintillator performance through advanced injection molding techniques

The production of plastic scintillators with superior optical properties, including high light yield and optimal emission spectra, plays a pivotal role in facilitating their extensive applicability across various domains. In addition, ensuring robust radiation hardness is essential for these scintillators to serve diverse purposes effectively. Given the significant impact of the optical gap on the optical characteristics and radiation resistance of scintillator products, we embarked on optimizing the injection molding technique, focusing on this critical parameter as part of the plastic scintillator fabrication process. Our findings indicate that the injection molding technique not only accelerates the fabrication process, but also yields products with comparable light yield and improved radiation hardness, outperforming samples produced by traditional thermal polymerization. These outcomes not only offer valuable insights and guidance for the streamlined production of high-quality plastic scintillators but also signify a notable advancement in this specialized field of study.

Enhanced radiation hardness of lead halide perovskite absorber materials via incorporation of Dy2+ cations

Continuously growing evidence of the excellent radiation hardness of perovskite solar cells stimulates their intense exploration in the context of potential aerospace applications. However, there is still a very limited understanding of the fundamental aspects such as the mechanisms of the interaction of complex lead halides with different types of ionizing radiation and associated aging pathways, even though this knowledge is essentially important for the development of new materials with improved properties. Herein, we made one of the first steps to fill this gap through a systematic study of the aging behavior of two perovskite absorber materials under exposure to three different stressors: 60Co gamma-rays, 8.5 MeV electron fluences, and light. The application of a set of complementary spectroscopy and microscopy techniques allowed us to identify and compare perovskite degradation pathways caused by each type of the ionizing radiation. In particular, radiation-induced phase segregation with the formation of δ-phases of CsPbI3 and FAPbI3 appears to be a common route in the case of double cation perovskites. Most importantly, we have revealed that the incorporation of dysprosium cations as a replacement of 1 % of Pb2+ ions in the Cs0.12FA0.88Pb0.99Dy0.01I3 material formulation results in a remarkably improved radiation hardness: this modification blocks the formation of metallic lead and strongly suppresses segregation of Cs-rich and FA-rich phases in perovskite films under exposure to gamma rays or high-energy electrons. Thus, these results open up a promising research direction for designing radiation-resistant perovskite absorbers through rational compositional engineering.

Improving Radiation Hardness of 4H-SiC Power Devices by Local-Oxidation of Silicon Carbide (LOCOSiC) Isolation

Improving Radiation Hardness of 4H-SiC Power Devices by Local-Oxidation of Silicon Carbide (LOCOSiC) Isolation

Designing and Reliability Analysis of Radiation Hardened Stacked Gate Junctionless FinFET and CMOS Inverter

Along with radiation sensing, necessity to study and design reliable radiation hardened devices is also increasing now-a-days. These devices are tolerant to high dosage of radiations without causing any physical damage, logic damage or data loss. In the current work, stacked gate Junctionless FinFET (SG JL FinFET) is analyzed as radiation hardened device by studying the impact of radiation of Linear Energy Transfer (LET) values ranging from 2MeV.cm/mg to 10MeV.cm/mg on the device performance. The proposed radiation hardened FinFET is experimentally calibrated with pre and post irradiation data. Single event upset (SEU) study using transient analysis is carried out to study the performance of proposed radiation hardened device at microwave frequency. High-k material-hafnium dioxide is used as gate oxide material to improve radiation hardness of SG JL FinFET. Electrical parameters-drain current, surface potential and SEU generation rate are studied to analyze device characteristics. Optimization of gate oxide, doping concentration, gate metals and temperature is carried out to enhance the reliability of device in terms of radiation hardness. SG JL FinFET is exposed to different types of waves-UV rays, X-ray, and Gamma rays to study the response of device at different frequencies. The comparison of SG JL and SG Inversion Mode (IM) FinFET has been performed. Comparison of SG JL FinFET with previously reported Inverted mode FinFET, L-shaped tunnel FET and Fully Depleted Silicon on Insulator (FD-SOI) MOSFET is carried out to find most suitable device which can provide highest immunity to radiation exposure. Response of JL FinFET based CMOS inverter in presence of radiation is studied and is also compared with other available CMOS inverters.

Design of Radiation Resistant Pre-amplifier for fusion reactors

The research of controlled nuclear fusion is not a simple process. The upcoming accomplishment of ITER means the beginning of a new phase of controlled nuclear fusion, which is building a fusion reactor. The operating electronics related to fusion reactors need to adapt to harsh environment and minimize the risk of any possible irradiation. Pre-amplifiers are widely used for signal conditioning in various diagnostic systems. And if not shielded, they would be easily damaged in a environment with strong radiation. In this study, a kind of Radiation Resistant Pre-amplifier (RRP) has been designed and manufactured. To verify its performance under radiation, tests in both gamma and neutron fields were carried out. And the performance of RRP is compared with that of an Ordinary Pre-amplifier (OP). The RRP was irradiated with gammas from a Co-60 source up to an accumulated dose of 1MGy, and was also irradiated with neutrons under a tandem accelerator up to a total neutron flux of 1013 n/cm2. The test results prove a performance improvement of radiation hardness on the RRP. And shielding optimization has been discussed with the circumstances of ITER port cell area in this paper. The RRP could better adapt to the complex irradiation environment of fusion reactors and possibly reduce shielding in the future.

Buried Layer Low Gain Avalanche Diodes

We report on the design, simulation and test of Low Gain Avalanche Diodes (LGADs) which utilize a buried gain layer. The buried layer is formed by patterned implantation of a 50-micron thick float zone substrate wafer-bonded to a low resistivity carrier. This is then followed by epitaxial deposition of a ≈ 3 micron-thick high resistivity amplification region. The topside is then processed with junction edge termination and guard ring structures and incorporates an AC-coupled cathode implant. This design allows for independent adjustment of gain layer depth and density, increasing design flexibility. A higher gain layer dopant density can also be achieved by controlling the process thermal budget, improving radiation hardness. A first set of demonstration devices has been fabricated, including a variety of test structures. We report on TCAD design and simulation, fabrication process flow, and preliminary measurements of prototype devices.

Improving radiation hardness in space-based Charge-Coupled Devices: an experimental validation of a new pre-fabrication modelling technique

The soft X-ray imager (SXI) on the SMILE mission uses two large 4510x4510 back illuminated CCD370s to detect X-rays in the 0.2–2 keV range. These devices take heritage from the optical imaging PLATO mission CCD270s and have been optimised for low energy signals by including a parallel supplementary buried channel (SBC) which should reduce the volume of the charge cloud and thereby reduce the number of traps it interacts with as it is transferred through the CCD.The charge transfer performance improvement between the CCD270 and the CCD370 has been simulated using a combination of Silvaco and Matlab models to predict its characteristics pre-fabrication over a 102–105 electron signal range. Trap pumping measurements have been taken on both devices to count the number of traps present and hence calculate the mean amount of traps that exist per pixel across the range of signal levels. The trap pumping results are used to calculate a charge transfer performance improvement that shows good agreement with the simulated values, especially in the SXI science band.These results bring added confidence to the early performance modelling of the SMILE SXI instrument and is a good indicator that the simulations are accurate enough to be used to model devices with more advanced geometries such as an SBC and can be used in future CCD missions, where radiation-hardness and hence good charge transfer characteristics are key.

Microscopic origin of the acceptor removal in neutron-irradiated Si detectors - An atomistic simulation study

The improved radiation hardness of p-type Si detectors is hindered by the radiation-induced acceptor removal process, which is not fully understood yet. Through atomistic modeling of displacement damage and dopant interactions, we analyze the acceptor removal under neutron irradiation, providing physical insight into its microscopic origin. Our results show that the fast decay of the effective dopant concentration (Neff) at low irradiation fluences is due to B deactivation caused by Si self-interstitials. The intriguing increase of the acceptor removal parameter with the initial dopant concentration (Neff,0) is explained by the limited number of mobile Si self-interstitials that survive annihilation and clustering processes. The sublinear dependence of the removal parameter on Neff,0 is associated to the inhomogeneity of damage for low Neff,0 and the formation of B-interstitial clusters with several B atoms for high Neff,0. The presence of O and C modifies B deactivation mechanisms due to the key role of BiO defects and the trapping of vacancies and Si self-interstitials, but for the impurity concentrations analyzed in this work ([O] >> [C]) it has little effect on the overall amount of removed acceptors. At high irradiation fluences, the reported increase of Neff is attributed to the formation of defect-related deep acceptors. From the analysis of the defect concentrations resulting from neutron irradiation and the occupancy of small clusters with acceptor levels reported in literature, we point out the tetra-vacancy cluster as one of the main contributors to Neff with negative space charge.

Charge collection efficiency study on neutron-irradiated planar silicon carbide diodes via UV-TCT

The material properties of silicon-carbide (SiC) make it a promising candidate for application as a particle detector at high beam rates. In comparison to silicon (Si), the increase in charge carrier saturation velocity and breakdown voltage allows for high intrinsic time resolution while mitigating pile-ups. A larger bandgap and higher atomic displacement threshold energy suppresses dark current and potentially improves radiation hardness, respectively. In addition to the lower susceptibility to temperature variations, it allows the operation of irradiated devices at room temperature and daylight illumination. Although already known for several decades, recent developments in industrial power electronics made SiC more accessible as a potential particle detector. Repeatability, large amplitudes and timing possibilities of signal pulses produced by the ultraviolet transient current technique (UV-TCT) allow for precise performance comparison of differing samples, while efficiently monitoring the influence of alternating external conditions. We present measurement results on the performance of neutron irradiated 4HSiC p-on-n planar diodes using such a setup. Dark current levels remain in the nA range for all fluences (5×1014neq/cm2−1×1016neq/cm2), while charge collection efficiency decreases with irradiation fluence, partially compensated when operating samples at reverse voltage conditions far above full depletion.

Evaluation of the Radiation Hardness of Photodiodes in 180-nm CMOS Technology for Medical Applications

Radiation-hard photodiode structures implemented in medical applications are designed in 180-nm CMOS technology. Designed photodiodes were tested against total ionizing doses (TIDs) of 100, 200, and 400 Gy(Si), respectively, and they show high stability in terms of dark current characteristics. After TID of 400 Gy(Si), the dark current increased by up to 15%, compared to the unirradiated characteristics values. TCAD electrical simulations were performed and calibrated with the dark current measurements in order to explain the impact of generated defects due to ionizing radiation. Parameters that are used to model TID radiation have been varied in physical boundaries in order to achieve the desired fitting with the measurements. It is shown that due to the filling of acceptor interface traps with electrons, the space charge region extends, but the extension is limited and partially compensated by the fixed positive charges in the silicon nitride layer. The presented photodiodes result in the improved radiation hardness over the design in 350-nm CMOS technology.

Carrier Lifetime in 60Co Gamma and 1 MeV Electron‐Irradiated Tin‐Doped n‐Type Czochralski Silicon: Conditions for Improving Radiation Hardness

Herein, the results that determine some conditions for increasing the radiation hardness of 60Co gamma or 1 MeV electron‐irradiated tin‐doped n‐type Czochralski silicon (Cz n‐Si:Sn) are presented. These conditions are determined from the analysis of the formation kinetics of dominant radiation defects (namely, VO and SnV complexes) and the recombination of charge carriers through the electronic levels of these defects in samples with different concentrations of phosphorus and tin. It is shown that low‐resistivity Cz n‐Si with P doping levels >5 × 1014 cm−3 containing in addition [Sn] ≈1017–1019 cm−3 has a radiation hardening potential. In this material, the radiation degradation of carrier lifetime is several times smaller compared with Sn‐free n‐Si, whereas the conductivity compensation is negligible for both materials. The reduction of the lifetime degradation rate is due to a reduction of VO concentration in low‐resistivity Cz n‐Si:Sn.

Current-voltage and capacitance-voltage characteristics of cadmium-doped p-silicon Schottky diodes

This study reports on a change in current-voltage (I–V) and capacitance-voltage (C–V) characteristics of silicon (Si) diodes due to doping Si with cadmium (Cd). Effects of Cd-doping on diode parameters and conduction mechanism are investigated. The results obtained here indicate that the diodes are well fabricated and introducing Cd in Si results in a diode I–V behaviour changing from normal exponential to ohmic. An ohmic behaviour indicates that the diode conduction mechanism is dominated by defect levels at the centre of the Si energy gap. These defects are responsible for generation of minority carriers to recombine majority carriers resulting in an increase in material resistivity. A change in a direction of a C–V trend showing an inversion of a material conductivity-type confirms the generation of minority carriers after doping Si with Cd. A high resistivity material is important for radiation detection since a full space charge region width can be attained at a reasonable operating voltage. The ohmic behaviour and a conductivity-type inversion have been observed on diodes that are resistant to radiation damage. Cd is, therefore, a suitable dopant in defect-engineering studies to improve radiation hardness of Si for high energy physics experiments.

Highly Resolved and Robust Dynamic X-Ray Imaging Using Perovskite Glass-Ceramic Scintillator with Reduced Light Scattering.

All‐inorganic perovskite quantum dots (QDs) CsPbX3 (X = Cl, Br, and I) have recently emerged as a new promising class of X‐ray scintillators. However, the instability of perovskite QDs and the strong optical scattering of the thick opaque QD scintillator film imped it to realize high‐quality and robust X‐ray image. Herein, the europium (Eu) doped CsPbBr3 QDs are in situ grown inside transparent amorphous matrix to form glass‐ceramic (GC) scintillator with glass phase serving as both matrix and encapsulation for the perovskite QD scintillators. The small amount of Eu dopant optimizes the crystallization of CsPbBr3 QDs and makes their distribution more uniform in the glass matrix, which can significantly reduce the light scattering and also enhance the photoluminescence emission of CsPbBr3 QDs. As a result, a remarkably high spatial resolution of 15.0 lp mm−1 is realized thanks to the reduced light scattering, which is so far a record resolution for perovskite scintillator based X‐ray imaging, and the scintillation stability is also significantly improved compared to the bare perovskite QD scintillators. Those results provide an effective platform particularly for the emerging perovskite nanocrystal scintillators to reduce light scattering and improve radiation hardness.

Commissioning and simulation of CHROMIE, a high-rate test beam telescope

The upgrade of the LHC to the High-Luminosity LHC (HL-LHC) is expected to increase the current instantaneous luminosity by a factor of 5 to 7, providing the opportunity to study rare processes and measure precisely the standard model parameters. To cope with the increase in pile-up (up to 200), particle density and radiation, CMS will build new silicon tracking devices with higher granularity (to reduce occupancy) and improved radiation hardness. During the R&D period tests performed under beam are a powerful way to develop and examine the behavior of silicon sensors in realistic conditions. The telescopes used up to now have a slow readout (less than 10 kHz) for the needs of the CMS experiment, since the new outer-tracker modules have an effective return-to-zero time of 25 ns (corresponding to a 40 MHz frequency) and a trigger rate of 750 kHz. In order to test the CMS Tracker modules under the LHC nominal rate, a pixel telescope named CHROMIE (CMS High Rate telescOpe MachInE) is designed, built and commissioned at CERN for beam tests with prototype modules for the CMS Phase-2 Tracker upgrade. In this article the design of CHROMIE, the calibration of its modules, and its timing and synchronization aspects are presented, along with the first beam test results. In addition, the tracking algorithm developed for CHROMIE and a preliminary Geant4 simulation study of the telescope under beam are discussed.

Radiation induced absorption of hydrogen-loaded pure silica optical fibers with carbon coating for ITER diagnostics

We present results of gamma irradiation tests of 200 μm pure silica core optical fibers with a low and high-OH concentration, with and without hydrogen loading. All the fibers were manufactured by a candidate supplier of the fiber bundles for optical plasma diagnostics in ITER. The hydrogen-loaded fibers were stored for a one year before the irradiation start. The fibers were exposed at two Co-60 gamma facilities using dose-rates of 15 and 194 mGy/s up to 15 and 70 kGy absorbed doses, respectively. The optical transmission losses of the fibers were measured in-situ in the spectral range of 450–900 nm. The results are interpreted on the basis of available data on radiation defects in silica core fibers. It is demonstrated that hydrogen loading provides a radiation hardness improvement, which allows to satisfy the ITER requirements.

CdSe/ZnS quantum dot encapsulated MoS2 phototransistor for enhanced radiation hardness

Notable progress achieved in studying MoS2 based phototransistors reveals the great potential to be applicable in various field of photodetectors, and to further expand it, a durability study of MoS2 phototransistors in harsh environments is highly required. Here, we investigate effects of gamma rays on the characteristics of MoS2 phototransistors and improve its radiation hardness by incorporating CdSe/ZnS quantum dots as an encapsulation layer. A 73.83% decrease in the photoresponsivity was observed after gamma ray irradiation of 400 Gy, and using a CYTOP and CdSe/ZnS quantum dot layer, the photoresponsivity was successfully retained at 75.16% on average after the gamma ray irradiation. Our results indicate that the CdSe/ZnS quantum dots having a high atomic number can be an effective encapsulation method to improve radiation hardness and thus to maintain the performance of the MoS2 phototransistor.

TRACS: A multi-thread transient current simulator for micro strips and pad detectors

The requisites at the Large Hadron Collider (LHC) at CERN have driven silicon tracking detectors to the fringe of the modern technology. The next upgrade of the LHC to a 10 times increased luminosity of 7.5×1034cm−2s−1 will require semiconductor detectors with substantially improved radiation hardness. CERN-RD50 collaboration mandate is to provide detector technologies, which are able to operate in such an environment. Within this context, this paper describes the approaches and first results of a C++11 multi-threading software based on the Shockley–Ramo’s theorem to simulate non-irradiated and irradiated silicon micro-strips and pad detectors of complex geometries in order to understand signal formation and charge collection efficiencies of arbitrary charge distributions.

Displacement Damage in Silicon Detectors for High Energy Physics

In this paper, we review the radiation damage issues caused by displacement damage in silicon sensors operating in the harsh radiation environments of high energy physics experiments. The origin and parameterization of the changes in the macroscopic electrical sensor properties such as depletion voltage, leakage current, and charge collection efficiency as a function of fluence of different particles, annealing time, and annealing temperature are reviewed. The impact of impurities in the silicon base crystal on these changes is discussed, revealing their effects on the degradation of the sensor properties. Differences on how segmented and nonsegmented devices are affected and how device engineering can improve radiation hardness are explained and characterization techniques used to study sensor performance and the electric field distribution inside the irradiated devices are outlined. Finally, recent developments in radiation hardening and simulation techniques using technology computer-aided design modeling are given. This paper concludes with radiation damage issues in presently operating experiments and gives an outlook of radiation-hardened technologies to be used in the future upgrades of the Large Hadron Collider and beyond.

OA055] Preliminary test of innovative strip silicon detectors for therapeutic proton beam monitoring

Purpose Unlike currently used gas ionization chambers, solid state detectors offer large granularity and sensitivity to single incoming particles, therefore being ideally suited to improve the present technology for beam monitoring in particle therapy. However, several drawbacks, such as radiation damage, prevented their use so far on high flux therapeutic beams. Two prototype devices for monitoring particle beams are under development, based on innovative silicon low-gain avalanche detectors optimized for time resolution (Ultra Fast Silicon Detectors – UFSDs). Preliminary results with proton beams are presented. Methods UFSDs are low-gain avalanche detectors optimized for time resolution, where sensors as thin as 50 μ m provide signals of ∼ 1 ns time duration with time resolutions of tenths of ps, and large enough signal-to-noise ratio to efficiently discriminate proton signal. One prototype device is being developed to directly count individual protons at high rates, while a second one is under investigation to measure the beam energy with time-of-flight techniques. This requires the design of custom UFSD sensors as well VLSI readout electronics. From simulations’ results and first beam tests with UFSD pads, strip detectors were produced, with two geometries (30 mm and 15 mm length) and different doping modalities to improve radiation hardness. In parallel, prototypes of a new readout chip have been submitted to the foundry. Results Strips sensors were characterized in the laboratory through laser test and I(V) curve studies, and a test with a therapeutic proton beam, with energy ranging from 62 to 227 MeV, was done. Results were obtained via offline analysis of the collected waveforms for Boron and Gallium doped sensors. Time resolution of 35 ps, signal duration of ns, and good S/N separation were found. A gain degradation of 20% was founded in single pad sensors after 10 12 protons/cm2 irradiation. Pile-up effects are under investigation. Conclusions Based on the preliminary results, UFSDs are found to be a promising improvement of monitor chamber. The aim of this contribution is to review the advancement of the project and to report on the results of the test of UFSD strip sensors with a therapeutic proton beam.