Online program Overview Session: JS-03

Abstract

Oxide passivation plays a critical role in stabilizing semiconductor radiation detectors by suppressing surface states and enabling low-leakage, high-resolution operation. In this work, Al₂O₃-passivated Ni/4H-SiC Schottky radiation detectors were fabricated on n-type epitaxial layers of varying thickness (20, 150, and 250 μm) using pulsed laser deposition without post-deposition annealing. All devices exhibit uniform rectification with Schottky barrier heights of ~1.3 eV, low interface trap density (~10⁹ cm⁻²eV⁻¹), and reverse leakage dominated by Poole-Frenkel transport. Capacitance-voltage measurements indicate a flat-band potential of ~2.3 V due to fixed oxide charge, while frequency dispersion confirms minimal contribution from slow interface states. Under 5.486 MeV α-particle irradiation, the detectors demonstrate efficient self-biased operation with energy resolution of 3.3% at 0 V, improving to ~0.5-0.6% at -40 V. A detailed comparison of two nominally identical 150 μm detectors reveals significant variation in charge collection efficiency (~0.99 vs ~0.6) and energy resolution despite similar electrical characteristics, indicating that bulk carrier trapping dominates performance variability. Deep-level transient spectroscopy identifies Z_1/2 centers as the primary recombination-active defects limiting resolution across all thicknesses. A broad high-energy feature is definitively resolved, for the first time in Al₂O₃-passivated 4H-SiC Schottky detectors, using isothermal transient spectroscopy into two distinct defect levels at E_C-1.05 eV and E_C-1.1 eV, attributed to oxide-related ON2a/b states. This work establishes a unified understanding of interface and bulk defect effects in SiC radiation detectors for optimizing high-resolution operation in harsh environments.

Abstract

Metal halide perovskite (MHP) has been widely investigated as a radiation scintillator. Current solution-processing methods used to fabricate the MHP film suffer from toxic solvent issues and are limited in their ability to scale up for a large area detector. Single-source vapour deposition offers a solvent-free alternative that uses a single precursor, making it a promising technique for scalable film fabrication. In this study, (BA)₂PbBr₄  films were fabricated using SSVD onto glass substrates under high vacuum. The films were subsequently characterised, and the X-ray scintillation performance was evaluated. The results revealed that SSVD produces a thick film with a mean thickness of 10.5 ± 4.0  um and has a polycrystalline grain distribution.   Energy-dispersive X-ray spectroscopy confirmed that the SSVD method preserved the composition, as the Br/Pb ratio is consistent with the theoretical value 4 for (BA)₂PbBr₄. Photoluminescence spectroscopy revealed a narrow peak emission 423 nm with FWHM 13 nm in close agreement with reported values for solution-grown crystals, confirming that the optoelectronic structure is preserved after deposition. Under 50 kVp X-ray irradiation, the film exhibited a fast, stable, linear dose rate response yielding scintillation sensitivity of 2464 µC Gy⁻¹ cm⁻². These results demonstrate that SSVD is a viable, solvent-free method for fabricating MHP scintillator films with direct implications for scalable fabrication for next-generation medical imaging detectors.

Abstract

Diamond is a highly promising semiconductor material for ionizing radiation detection. Diamond-based detectors are excellent candidates for neutron detection due to interactions on relatively light carbon nuclei. Moreover, these detectors exhibit low sensitivity to X-ray and gamma radiation that often accompany neutron flux. Neutrons with energies below approximately 6 MeV are detected solely via elastic scattering on carbon nuclei within the diamond crystal. At higher energies, nuclear reactions occur, producing alpha particles, protons, and ions that can be detected by the detector. In this experiment, we use a single-crystal CVD diamond detector to detect fast neutrons with energies ranging from 300 keV to 18.5 MeV. A diamond detector has square contact dimensions of 3.6 × 3.6 mm² and a thickness of 0.5 mm. Testing the detector with an alpha-particle source showed a high-energy resolution of about 0.4% at 5.5 MeV. The detector was used to detect monoenergetic neutrons ranging from 250 keV to 911 keV, 3.5 MeV to 4.5 MeV, and 14.6 MeV to 18.5 MeV, generated by p-T, D-D, and D-T nuclear reactions at Van de Graaff accelerator, respectively. The single-crystal diamond detector showed good linearity and excellent detection properties. In the detected spectra, all main neutron-detector interactions were identified.

Abstract

We investigated ways to improve the spectral resolution of a Timepix3 hybrid pixel detector with a 1 mm thick silicon sensor for X-ray and soft gamma photons. A standard procedure is to calibrate the time-over-threshold (ToT) to deposited energy for each pixel, but even then, there remains room for improvement. The first improvement was lowering the Krummenacher current (Ikrum) to increase the ToT at even low-energy deposits to get a finer resolution. The second novel improvement was creating an additional calibration on cluster energies, taking into account the cluster size. It was observed that clusters of larger size feature a higher energy than smaller clusters created by the same photon source. The cluster energy could therefore be corrected based on its size, and we found that this correction is linear for each cluster size. Both the lowering of the Ikrum together with the cluster size correction decreased the full width at half maximum (FWHM) by 17-35 % compared to the initial settings in the energy range of 4-136 keV. The higher the photon energy, the larger the percentage decrease in FWHM. We intend to utilize the enhanced spectral resolution in Compton X-ray polarimetry. There, the coincident events of a Compton scattering followed by a photoabsorption are measured. The sum of the deposited energies in the two events gives the original energy of the photon. The FWHM of coincident pairs of clusters decreased by 22-44 % compared to the initial settings in the energy range of 43-136 keV.

Abstract

Accurate interaction position reconstruction in radiation detectors is often limited by the lack of tractable likelihood functions and the stochastic nature of particle transport and charge induction processes. In this work, we present a simulation-based inference framework for 3D Cadmium Zinc Telluride drift strip detectors (3D CZT DSD) that learns a probabilistic inverse mapping from Charge Induction Efficiency signals to interaction positions using Monte Carlo generated training data. We formulate the reconstruction problem as Neural Posterior Estimation and train a neural network to predict a Gaussian approximation of the posterior distribution over interaction positions. The model is optimized using negative log-likelihood, enabling simultaneous estimation of interaction positions and associated uncertainties in a single amortized inference step. Preliminary results on synthetic datasets show that the proposed method produces meaningful uncertainty estimates that provide insights into detector response variability compared to deterministic regression approaches.

Abstract

The cadmium zinc TElluride Radiation Imager (TERI) was successfully launched to the International Space Station (ISS) on April 21, 2025 as a part of the Department of Defense’s Space Test Program (STP-H10) mission. The primary mission of TERI is to space-qualify large-volume 4×4×1.5 cm³ pixelated CdZnTe (CZT) detectors. The system is composed of four of these advanced detectors, each of which is 3D position sensitive, allowing for Compton event imaging. Here, we report on the one-year in-orbit performance results of TERI, including measurements of the background rate, which align with expected orbital variations. We analyze the 511 keV line and observe no significant degradation over nine months in orbit. Additionally, we observe multiple spectral lines, several of which are consistent with known activation lines.