arXiv subjects

Andreas Gsponer

Publications and source records attributed to Andreas Gsponer.

17 recordsLinked to original sources

arXiv2025

Design and simulation of a 4H-SiC low gain avalanche diode with trench-isolation

We present the design and simulation of a 30 $\mathrm{\mu m}$ thick 4H-SiC Low Gain Avalanche Diode (LGAD) optimized for high-voltage operation. A 2.4 $\mathrm{\mu m}$ thick epitaxially grown gain layer enables controlled internal amplification up to 1 kV reverse bias, while maintaining full depletion below 500 V. Electrical characteristics, including I-V, C-V, and gain behavior, were simulated in Synopsys Sentaurus Technology Computer-Aided Design (TCAD) using a quasi-1D geometry and verified across process-related variations in gain layer parameters. To ensure high-voltage stability and proper edge termination, a guard structure combining deep etched trenches and deep $p^+$ junction termination extension (JTE) implants was designed. TCAD simulations varying the guard structure dimensions yielded an optimized design with a breakdown voltage above 2.4 kV. A corresponding wafer run is currently processed at IMB-CNM, Barcelona.

physics.ins-det↗

arXiv2025

In-situ Radiation Damage Study of Silicon Carbide Detectors Subjected to Clinical Proton Beams

Silicon carbide (SiC) planar PiN diodes from two different manufacturers were irradiated with 252.7 MeV protons from a medical synchrotron. Over the course of two 8h irradiation shifts, the samples were exposed to increasing fluences ranging from 1.4e+11 to 3.5e+13 p+/cm^2. Electrical characterizations, including IV and CV measurements, were performed both before and after irradiation using probe stations, and for selected samples even in-situ between fluence steps directly at the irradiation facility. The results show a gradual compensation of the effective epitaxial doping concentration with each incremental fluence step, observed as a reduction in capacitance before full depletion and confirmed by the extracted effective doping concentration. From these measurements, linear donor removal rates are determined for all sample groups, with values ranging from 4.2/cm to 6.4/cm. These findings provide a quantitative basis for understanding radiation-induced charge carrier removal in 4H-SiC devices and are relevant for predicting the performance and lifetime of future radiation-hard detector technologies, including 4H-SiC LGADs.

physics.ins-det↗

arXiv2025

Extraction of Electron and Hole Drift Velocities in thin 4H-SiC PIN Detectors using High-Frequency Readout Electronics

Silicon carbide (SiC) has been widely adopted in the semiconductor industry, particularly in power electronics, because of its high temperature stability, high breakdown field, and fast switching speeds. Its wide band gap makes it an interesting candidate for radiation-hard particle detectors in high-energy physics and medical applications. Furthermore, the high electron and hole drift velocities in 4H-SiC enable devices suitable for ultra-fast particle detection and timing applications. However, currently, the front-end readout electronics used for 4H-SiC detectors constitute a bottleneck in investigations of the charge carrier drift. To address these limitations, a high-frequency readout board with an intrinsic bandwidth of 10 GHz was developed. With this readout, the transient current signals of a 4H-SiC diode with a diameter of 141 $\mathrm{\mu m}$ and a thickness of 50 $\mathrm{\mu m}$ upon UV-laser, alpha particle, and high-energy proton beam excitation were recorded. In all three cases, the electron and hole drift can clearly be separated, which enables the extraction of the charge carrier drift velocities as a function of the electric field. These velocities, for the first time directly measured, provide a valuable comparison to Monte-Carlo simulated literature values and constitute an essential input for TCAD simulations. Finally, a complete simulation environment combining TCAD, the Allpix$^2$ framework, and SPICE simulations is presented, in good agreement with the measured data.

physics.ins-det↗

arXiv2025

Characterizing the Delivered Spill Structure of Medical Proton and Carbon-Ion Beams at MedAustron using a High Frequency Silicon Carbide Readout

Medical synchrotrons are often used for testing instrumentation in high-energy physics or non-clinical research in medical physics. In many applications of medical synchrotrons, such as microdosimetry and ion imaging, precise knowledge of the spill structure and instantaneous particle rate is crucial. Conventional ionization chambers, while omnipresent in clinical settings, suffer from limitations in charge resolution and integration time, making single-particle detection at high dose rates unfeasible. To address these limitations, we present a beam detection setup based on a silicon carbide (SiC) sensor and a monolithic microwave integrated circuit (MMIC), capable of detecting single particles with a full width at half maximum (FWHM) pulse duration of 500 ps. At the MedAustron ion therapy center, we characterized the spill structure of proton and carbon-ion beams delivered to the irradiation room beyond the timescale of the maximum ion revolution frequency in the synchrotron. The resulting data offer valuable insights into the beam intensity at small time scales and demonstrate the capabilities of SiC-based systems for high-flux beam monitoring.

physics.ins-det↗

arXiv2025

From Single Particles to Clinical Beam Rates: A Wide Dynamic Range Beam Monitor

Access to high-energy particle beams is key for testing high-energy physics (HEP) instruments. Accelerators for cancer treatment can serve as such a testing ground. However, HEP instrument tests typically require particle fluxes significantly lower than for cancer treatment. Thus, facilities need adaptations to fulfill both the requirements for cancer treatment and the requirements for HEP instrument testing. We report on the progress made in developing a beam monitor with a sufficient dynamic range to allow for the detection of single particles, while still being able to act as a monitor at the clinical particle rates of the MedAustron treatment facility. The beam monitor is designed for integration into existing accelerators.

physics.acc-ph↗

arXiv2025

A double multi-turn injection scheme for generating mixed helium and carbon ion beams at medical synchrotron facilities

The low relative charge-to-mass ratio offset of 0.065% between fully ionized helium-4 and carbon-12 ions enables simultaneous acceleration in hadron therapy synchrotrons. At the same energy per mass, helium ions exhibit a stopping range approximately three times greater than carbon ions. They can therefore be exploited for online range verification downstream of the patient during carbon ion beam irradiation. One possibility for creating this mixed beam is accelerating the two ion species sequentially through the LINAC and subsequently "mixing" them at injection energy in the synchrotron with a double multi-turn injection scheme. This work reports the first successful generation, acceleration, and extraction of a mixed helium and carbon ion beam using this double multi-turn injection scheme, which was achieved at the MedAustron therapy accelerator in Austria. A description of the double multi-turn injection scheme, particle tracking simulations, and details on the implementation at the MedAustron accelerator facility are presented and discussed. Finally, measurements of the mixed beam at delivery in the irradiation room using a radiochromic film and a low-gain avalanche diode (LGAD) detector are presented.

physics.acc-ph↗

arXiv2024

Observation of Charge Enhancement in forward-biased neutron-irradiated 4H-SiC PiN Detectors in UV-TCT Measurements

Due to the increased commercial availability, wide-bandgap semiconductors and their radiation hardness have recently received increased interest from the particle physics community. 4H-Silicon Carbide (SiC), especially, is an attractive candidate for future radiation-hard detectors which do not require cooling. This paper investigates the radiation hardness of 4H-SiC p-in-n detectors irradiated up to $5\times 10^{15}$ $\text{n}_{\text{eq.}}/\text{cm}^2$ using UV-TCT. The samples have been operated in reverse and forward bias, which is possible due to the heavily decreased forward current after irradiation. Previous studies have already hinted at an excessive charge collection in forward bias, even exceeding a charge collection efficiency (CCE) of 100%. In this work, the excessive CCE in forward bias was shown to correlate heavily with the spatial profile of injected charge. For a sufficiently focused laser, the CCE starts to increase at high forward bias and even surpasses 100% instead of saturating as it does for a defocused laser beam. In reverse bias, the CCE was found to be independent of the beam spot size. For samples irradiated to high fluences ($\geq 1\times 10^{15}$ $\text{n}_{\text{eq.}}/\text{cm}^2$) the excessive CCE in forward bias is smaller and negligible at the highest fluences. Additionally, the CCE was observed to correlate to the rate of charge injection (laser pulses per second), with a logarithmic increase of the collected charge if a threshold of injected carrier density is exceeded. The mechanism of these effects is still an ongoing topic of study, however, the observations already pose implications for the accurate experimental characterization of irradiated SiC detectors.

physics.ins-det↗

arXiv2024

TCAD Parameters for 4H-SiC: A Review

In this literature review we investigate the permittivity, density-of-state mass, band gap, impact ionization, charge carrier recombination, incomplete ionization and mobility in 4H silicon carbide. We provide a comprehensive overview over characterization methods, models and parameters to lower the entrance barrier for newcomers and allow a critical evaluation of common material property descriptions. We further highlight areas for future research by identifying gaps in the current knowledge base. For each investigated property we found a large amount of models and parameter sets based on measurements, calculations or fittings. With literal and/or graphical comparisons we reveal qualitative good agreement but also flawed data values, misinterpretations of research results and inconsistencies among multiple investigations, even those directly referencing each other. We identify parameter variations, e.g., due to temperature, with high impact that are rarely considered in 4H-SiC analyses and common values that are based on old research of deviating materials or properties. We further show the slow accommodation of recent research results within the scientific community and reveal missing characterization data but also insufficient models in state-of-the-art technology computer aided design (TCAD) tools. Overall, our review enables scientifically based decisions on 4H-SiC material parameters and unravels the demand for further investigations to validate commonly used values, confirm hypothesis and cover additional dependencies.

cond-mat.mtrl-sci↗

arXiv2024

TCAD Simulations of Radiation Damage in 4H-SiC

To increase the scientific output of particle physics experiments, upgrades are underway at all major accelerator facilities to significantly improve the luminosity. Consequently, the solid-state detectors used in the experiments will exhibit more severe radiation-induced damage. To ensure sufficiently long sensor lifetimes, alternative materials to the established silicon sensors, with improved resilience to radiation, are investigated. For one of the promising candidate materials, silicon carbide, only recently a model describing the radiation damage in technology aided computer design (TCAD) simulations has been proposed. In this paper we present our latest achievements towards modeling radiation damage of 4H-SiC in TCAD tools. We first verify the utilized TCAD framework against published silicon data and then use it to approximate measurements of neutron-irradiated 4H-SiC particle detectors. We are able to confirm in simulations the measurement results, i.e., an almost flat capacitance as a function of bias voltage and a decreasing forward current with increasing particle fluence. Based on our simulations we are able to explain the latter by trapped charge carriers that create a space charge region within the device.

physics.ins-det↗

arXiv2024

The ECFA Early-Career Researchers Panel: Report for the year 2023

The European Committee for Future Accelerators (ECFA) Early-Career Researcher (ECR) panel, which represents the interests of the ECR community to ECFA, presents in this document its initiatives and activities in the year 2023. This report summarises the process of the first big turnover in the panel composition at the start of 2023 and reports on the activities of the active working groups - either pursued from before or newly established. The overarching goal of the ECFA-ECR panel is to better understand and support the diverse interests of early-career researchers in the ECFA community and beyond.

physics.acc-ph↗

arXiv2024

TCAD modeling of radiation-induced defects in 4H-SiC diodes

Silicon Carbide (SiC) has several advantageous properties compared to Silicon (Si) that make it an appealing detector material, such as a larger charge carrier saturation velocity, bandgap, and thermal conductivity. While the current understanding of material and model parameters suffices to simulate unirradiated 4H-SiC devices using technical computer-aided design (TCAD), configurations to accurately predict performance degradation after high levels of irradiation due to induced defects acting as traps and recombination centers do not exist. Despite increasing efforts to characterize the introduction and nature of such defects in 4H-SiC, published results are often contradictory. This work presents a bulk radiation damage model for TCAD simulations based on measurements on 50 $\mu m$ 4H-SiC pad diodes, neutron-irradiated at various fluxes ranging from $5\times 10^{14}$ $n_{eq}/cm^2$ to $1\times 10^{16}$ $n_{eq}/cm^2$. The model accurately predicts internal electric shifts, such as flattening of the detector capacitance, degradation in charge collection efficiency (CCE), and signal detection capabilities under forward bias conditions up to high bias. It further introduces the EH$_4$ defect cluster as major lifetime killer and reinforces the assumption of the EH$_{6,7}$ deep-level defect to be of donor type.

physics.ins-det↗

arXiv2023

Pulsed RF Knock-Out Extraction: A Potential Enabler for FLASH Hadrontherapy in the Bragg Peak

One challenge on the path to delivering FLASH-compatible beams with a synchrotron is facilitating an accurate dose-control for the required ultra-high dose rates. We propose the use of pulsed RFKO extraction instead of continuous beam delivery as a way to control the dose delivered per Voxel. In a first feasibility test dose rates in pulses of up to 600 Gy/s were observed, while the granularity at which the dose was delivered is expected to be well below 0.5 Gy.

physics.med-ph↗

arXiv2023

Measurement of the electron-hole pair creation energy in a 4H-SiC p-n diode

For 4H silicon carbide (4H-SiC), the values for the electron-hole pair creation energy $\epsilon_{\text{i}}$ published in the literature vary significantly. This work presents an experimental determination of $\epsilon_{\text{i}}$ using $50$ $\mu$m 4H-SiC p-n diodes designed for particle detection in high-energy physics. The detector response was measured for $\alpha$ particles between 4.2 MeV and 5.6 MeV for 4H-SiC and a silicon reference device. Different $\alpha$ energies were obtained by using multiple nuclides and varying the effective air gap between the $\alpha$ source and the detector. The energy deposited in the detectors was determined using a Monte Carlo simulation, taking into account the device cross-sections. A linear fit of the detector response to the deposited energy yields $\epsilon_{\text{i}} = (7.83 \pm 0.02)\;\text{eV}$, which agrees well with the most recent literature. For the 4H-SiC detectors, a linewidth of 28 keV FWHM was achieved, corresponding to an energy resolution of 0.5\%.

physics.ins-det↗

arXiv2023

SiC Based Beam Monitoring System for Particle Rates from kHz to GHz

The extremely low dark current of silicon carbide (SiC) detectors, even after high-fluence irradiation, was utilized to develop a beam monitoring system for a wide range of particle rates, i.e., from the kHz to the GHz regime. The system is completely built from off-the-shelve components and is focused on compactness and simple deployment. Beam tests using a 50 um thick SiC detector reveal, that for low fluences, single particles can be detected and counted. For higher fluences, beam properties were extracted from beam cross sections using a silicon strip detector. Overall accurate results were achieved up to a particle rate of 109 particles per second.

physics.ins-det↗

arXiv2023

Neutron Radiation induced Effects in 4H-SiC PiN Diodes

Silicon carbide (SiC) is a wide band gap semiconductor and an attractive candidate for applications in harsh environments such as space, fusion, or future high luminosity colliders. Due to the large band gap, the leakage currents in SiC devices are extremely small, even after irradiation to very high fluences, enabling operation without cooling and at high temperatures. This study investigates the effect of neutron irradiation on 50$μ$m p-n 4H-SiC diodes using current-voltage, capacitance-voltage, and charge collection efficiency (CCE) measurements up to neutron fluences of $1\times 10^{16}$ n$_{\text{eq}}$/cm$^2$. The leakage currents of the investigated devices remained extremely small, below 10 pA at 1.1 kV reverse bias. In the forward bias, a remarkable drop of the current was observed, which was attributed to an increased epi resistivity due to compensation of the epi layer doping by deep-level defects. The CCE was evaluated for alpha particles from a radioactive source, a 62.4 MeV proton beam at the MedAustron ion therapy center and using UV-TCT. The charge collection efficiency in reverse bias was shown to scale directly with the 1 MeV equivalent fluence $Φ_{\text{eq}}$ as $\text{CCE} \propto Φ_{\text{eq}}^{-0.63\pm0.01}$. A CCE better than 50% was able to be obtained for fluences up to $1 \times 10^{15}$ n$_{\text{eq}}$/cm$^2$. Because of the low currents in the forward direction, particle detection was also possible in forward bias, where the CCE was found to be increased relative to reverse bias. Furthermore, a significant dependency on the amount of injected charge was observed, with the CCE surpassing 100% in alpha and UV-TCT measurements, requiring further systematic investigation.

physics.ins-det↗

arXiv2022

Performance of neutron-irradiated 4H-Silicon Carbide diodes subjected to Alpha radiation

The unique electrical and material properties of 4H-silicon-carbide (4H-SiC) make it a promising candidate material for high rate particle detectors. In contrast to the ubiquitously used silicon (Si), 4H-SiC offers a higher carrier saturation velocity and larger breakdown voltage, enabling a high intrinsic time resolution and mitigating pile-up effects. Additionally, as radiation hardness requirements grow more demanding, wide-bandgap materials such as 4H-SiC could offer better performance. In this work, the detector performance of 50 micron thick 4H-SiC p-in-n planar pad sensors was investigated at room temperature, using an 241Am alpha source at reverse biases of up to 1100 V. Samples subjected to neutron irradiation with fluences of up to 1e16/cm^2 were included in the study in order to quantify the radiation hardness properties of 4H-SiC. The obtained results are compared to previously performed UV-TCT studies. Samples exhibit a drop in charge collection efficiency (CCE) with increasing irradiation fluence, partially compensated at high reverse bias voltages far above full depletion voltage. A plateau of the collected charges is observed in accordance with the depletion of the volume the alpha particles penetrate for an unirradiated reference detector. For the neutron-irradiated samples, such a plateau only becomes apparent at higher reverse bias. For the highest investigated fluence, CCE behaves almost linearly with increasing reverse bias. Compared to UV-TCT measurements, the reverse bias required to deplete a sensitive volume covering full energy deposition is lower, due to the small penetration depth of the alpha particles. At the highest reverse bias, the measured CCE values agree well with earlier UV-TCT studies, with discrepancies between 1% and 5%.

physics.ins-det↗

arXiv2022

New Limit on Axion-Like Dark Matter using Cold Neutrons

We report on a search for dark matter axion-like particles (ALPs) using a Ramsey-type apparatus for cold neutrons. A hypothetical ALP-gluon-coupling would manifest in a neutron electric dipole moment signal oscillating in time. Twenty-four hours of data have been analyzed in a frequency range from 23 $\mu$Hz to 1 kHz, and no significant oscillating signal has been found. The usage of present dark-matter models allows to constrain the coupling of ALPs to gluons in the mass range from $10^{-19}$ to $4 \times 10^{-12}$ eV. The best limit of $C_G$/$f_a m_a = 2.7 \times 10^{13}$ GeV$^{-2}$ (95\% C.L.) is reached in the mass range from $2 \times 10^{-17}$ to $2 \times 10^{-14}$ eV.

hep-ex↗