arXiv subjects

David Novák

Publications and source records attributed to David Novák.

4 recordsLinked to original sources

arXiv2026

Effects of irradiation by protons, neutrons, and gamma particles on electrical properties of 4H-SiC diodes and LGAD sensors

4H-SiC is a wide-bandgap semiconductor with high displacement threshold energy, large critical electric field, and low intrinsic carrier concentration, making it attractive for radiation-hard detector applications. In this work, we investigate the electrical characteristics of 4H-SiC P$^{+}$-in-N (PN) diodes and Low-Gain Avalanche Detectors (LGADs) fabricated by onsemi before and after irradiation by 24 GeV/c protons, reactor neutrons, and $^{60}$Co gamma rays. Current-voltage (IV) and capacitance-voltage (CV) measurements were performed at room temperature for proton fluences up to $1\times10^{16}\;\mathrm{protons/cm^2}$, neutron fluences up to $1\times10^{18}\;\mathrm{1\;MeV\;n_{eq}/cm^2}$, and total ionizing doses up to 300 kGy. Hadron irradiation induces pronounced changes in both leakage current and bulk capacitance, consistent with radiation-induced formation of deep acceptor-like defects and strong compensation of the originally N-type material. For high proton fluences, the leakage current decreases and the bulk capacitance becomes bias-independent, indicating effective compensation of the epitaxial layer. Extreme neutron fluences lead to a substantial expansion of the depleted region into the originally highly doped substrate, as inferred from the measured capacitance values. Gamma irradiation up to 300 kGy results in significantly modified capacitance behavior, suggesting reduction of the effective doping concentration in the epitaxial and multiplication layers. The results demonstrate that radiation-induced compensation strongly modifies the effective space charge in 4H-SiC devices at high hadron fluences, while the leakage current is influenced by the enlarged depletion volume together with field-enhanced and surface-related generation mechanisms. In contrast, ionizing damage primarily affects the effective doping and electric-field distribution.

physics.ins-det↗

arXiv2026

Page image classifier fine-tuned on century-spanning archives of scanned documents for further content-specific processing

Purpose: Digitization projects in the humanities produce vast, heterogeneous archives of historical documents, making manual sorting impractical at scale. This work addresses the need for an automated system to classify scanned page images based on visual content type - text, tables, and graphics - enabling content-specific downstream processing such as Optical Character Recognition (OCR) or structured data extraction. Methods: An image classification system was developed and evaluated on a dataset of over 48,000 annotated historical page images from century-old Czech archaeological archives, refined through four successive annotation stages with domain-expert review. A Random Forest Classifier baseline was established using hand-crafted image features. Subsequently, deep learning architectures were fine-tuned and compared: Convolutional Neural Networks (EfficientNetV2, RegNetY), Vision and Document Image Transformers (ViT, DiT), and multimodal CLIP models. An 11-category label scheme was designed collaboratively with domain experts and evaluated via five-fold cross-validation. Results: The feature-based baseline achieved approximately 75% accuracy. Fine-tuned CNNs and Transformers substantially outperformed it, with RegNetY-16GF achieving 99.16% and ViT-large 99.12% Top-1 accuracy on the held-out test set. CLIP ViT-B/16 reached 99.14% with optimized text descriptions. Conclusion: Image-only models, particularly RegNetY-16GF, deliver near-perfect classification accuracy and produce consistent labels across 649,508 unlabeled archival pages with over 90% inter-model agreement. Fine-tuned CLIP, despite competitive test-set accuracy, showed under 65% agreement with image-only models on unlabeled data, making it less suitable for deployment. The final models, annotated dataset, and software are publicly available under open-source licenses.

cs.CV↗

arXiv2026

Exploring the Design and Measurements of Next-Generation 4H-SiC LGADs

This contribution presents the design, production, and initial testing of newly developed 4H-SiC Low Gain Avalanche Detectors (LGADs). The evaluation includes performance metrics such as the internal gain layer's efficiency in enhancing signal generation. Initial laboratory and Transient Current Technique (TCT) measurements provide insight into the device's stability and response to the signal. Due to the increase of availability provided by the industry, 4H-SiC is emerging as a strong candidate for the next-generation of semiconductor detectors. Such sensors are promising due to the inherent radiation tolerance of 4H-SiC and its stable operation across a wide temperature range. However, due to the wider-bandgap of 4H-SiC compared to standard silicon, and difficulty to produce high-quality layers thicker than 50 \textmu m, an internal charge multiplication layer needs to be introduced. The presented 4H-SiC LGADs, fabricated by onsemi, are optimized for an N-type substrate and epi wafer. The initial TCT and laboratory test results demonstrate fast charge collection and uniform multiplication across multiple samples produced on a single wafer.

physics.ins-det↗

arXiv2025

First generation 4H-SiC LGAD production and its performance evaluation

This contribution will delve into the design and performance of the newly produced Silicon Carbide Low Gain Avalanche Detectors (4H-SiC LGADs) and provide a comprehensive summary of their measured characteristics. This includes an analysis of the detector's performance, temperature stability, and the effectiveness of the internal gain layer in improving signal generation. The 4H-SiC is re-emerging as a strong candidate for the next generation of semiconductor detectors. This material offers several advantages, including high radiation tolerance and the ability to operate over a wide range of temperatures without significant annealing effects. However, the signals generated by minimum ionizing particles in the 4H-SiC detector are lower compared to the signal produced by standard silicon detectors due to their higher bandgap energy. This is addressed by implementing a charge multiplication layer, which results in the intrinsic gain of the device. The presented 4H-SiC LGADs produced by onsemi are specifically designed and optimized for fabrication on the n-type substrate/epi wafer with the gain layer implanted approximately $1~\mathrm{μm}$ below the surface. The first iteration of these LGAD structures was manufactured in early 2024 and since then has been subjected to laboratory evaluation. The measured properties of these detectors align well with the predictions arising from the extensive TCAD simulation studies.

physics.ins-det↗