arXiv subjects

Moritz Wiehe

Publications and source records attributed to Moritz Wiehe.

6 recordsLinked to original sources

arXiv2026

TPA-TCT analysis of the RD50-MPW4 monolithic pixel particle detector

The RD50-MPW4, a Depleted Monolithic Active Pixel Sensor (DMAPS) was analyzed using a Two Photon Absorption Transient Current Technique (TPA-TCT). This technique provides sensitivity maps with micrometer-scale spatial resolution, enabling the resolution of the boundaries of the detector's sensitive volume, even for small-area pixels (62 x 62 $\mu$m$^2$ in this study). With a 3D resolution, the depletion depth, the boundaries of the detector electric field, the 3D hit detection efficiency and the charge sharing between neighboring pixels were measured. The RD50-MPW4, a multi-project wafer chip developed by the HV-CMOS working group within the CERN RD50 collaboration, features a 64 x 64 DMAPS pixel matrix. Illuminating the chip from the backside, the TPA-TCT technique can characterize any pixel element in the matrix because silicon is transparent for near infrared laser light (1550 nm). Electron-hole pairs are generated only around the light focal point, deep in the silicon, so that any charge collected is precisely only from the focal point. With the TPA-TCT technique, the RD50-MPW4 was found to be have a 100% hit detection efficiency under specified conditions and an effective depletion depth of 226 $\mu$m. It was also found that part of the charge in the periphery of the pixel was collected in the neighboring pixel. A 3D map of the sensor clearly shows the in-pixel electronics and the limits of the depletion region.

physics.ins-det↗

arXiv2025

Defects and acceptor removal in 60Co {\gamma}-irradiated p-type silicon

Boron-doped silicon detectors used in high radiation environments like the future HL-LHC show a degradation in device performance due to the radiation induced deactivation of the active boron dopant. This effect, known as the so-called Acceptor Removal Effect (ARE), depends on particle type, particle energy and radiation dose and is usually explained by the formation of boroninterstitial - oxygen-interstitial (BiOi) defects that induce a donor-type defect level in the upper part of the Si band gap. Here we present defect characterization studies using Thermally Stimulated Current technique (TSC) and Deep Level Transient Spectroscopy (DLTS) on a set of epitaxially grown p-type silicon diodes of different resistivity, irradiated with 60Co {\gamma}-rays. We used the defect parameters (activation energy, charge carrier capture cross sections and defect concentration) obtained from DLTS experiments for modeling the corresponding TSC spectra, and subsequently compared those with the experimental TSC results. This approach shows that the di-vacancy which is well characterized by DLTS correlates with the so-far unspecified charge emission signal of the X-defect that partially overlaps with the BiOi peak in TSC spectra. Additionally, in order to evaluate the impact of BiOi defect formation on the macroscopic properties of the device, we compared the BiOi defect concentration with the change in the effective carrier concentration Neff obtained from C-V measurements. It shows that the variations in Neff are about twice the changes in the BiOi concentration, which is in perfect consistency with the assumption of boron deactivation by the formation of the BiOi donor in irradiated p-type Si.

hep-ex↗

arXiv2025

Characterisation of Crystalline Defects in 4H Silicon Carbide using DLTS and TSC

Future hadron collider experiments will require sensing materials that withstand stronger radiation fields. Therefore, either a frequent replacement of detectors, a significant increase in radiation hardness of Silicon, or a shift to different materials is needed. Wide-bandgap materials are a natural choice, due to their significantly reduced leakage currents, even after irradiation. In recent years, substantial progress in the production of high-quality monocrystalline Silicon Carbide of the 4H polytype has led to a renewed interest in this material. In this article, a study of electrically active defects in a n-type epitaxial 4H Silicon Carbide diode is presented. By employing spectroscopical measurement methods, like Deep-Level Transient Spectroscopy (DLTS) and Thermally Stimulated Currents (TSC), energy levels in the bandgap are investigated. Defect parameters like concentration, activation energy and capture cross-section are stated. A simulation framework was utilised to compare and match the results from the two methods. This study is made in the context of a study of radiation hardness of 4H Silicon Carbide sensors. Other studies investigating macroscopic properties of the material, like their charge collection efficiency after irradiation, were performed on the same kind of diodes. This study provides a first set of measured defect parameters in state-of-the-art 4H-SiC material, from defects present prior to irradiation. These defects are intrinsic, such as vacancies, related to impurities and doping imperfections, or are growth related. The $Z_\text{1/2}$ defect and a Nitrogen related defect were identified.

physics.ins-det↗

arXiv2025

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

Investigating irradiation effects and space charge sign inversion in n-type Low Gain Avalanche Detectors

Low Gain Avalanche Detectors built on n-type substrate (nLGADs) have been developed by IMB-CNM to enhance the detection of low-penetrating particles, with a wide range of applications from medicine, industry to synergies with developments for high-energy physics (HEP). In this work, irradiation effects on nLGADs were investigated through proton irradiation at the CERN PS-IRRAD facility up to proton fluences of $10^{14}\,\mathrm{cm}^{-2}$. Electrical characterization before and after irradiation reveals space charge sign inversion of the n-type bulk, leading to significant modifications in the depletion behavior and electric field distribution. Utilizing UV TCT and TPA-TCT measurements, the impact of irradiation on the electric fields and the gain are studied in more detail, confirming a change of sensor depletion and a reduced electric field in the gain layer. The results suggest that donor removal in nLGADs is stronger pronounced already at lower fluences compared to acceptor removal in traditional p-type LGADs. These findings provide not only first insights into the effects of irradiation on nLGADs but also contribute to the development of methods to quantify the donor removal.

physics.ins-det↗

arXiv2024

TCAD Simulation of Two Photon Absorption -- Transient Current Technique measurements on Silicon Detectors and LGADs

Device simulation plays a crucial role in complementing experimental device characterisation by enabling deeper understanding of internal physical processes. However, for simulations to be trusted, experimental validation is essential to confirm the accuracy of the conclusions drawn.In the framework of semiconductor detector characterisation, one powerful tool for such validation is the Two Photon Absorption - Transient Current Technique (TPA-TCT), which allows for highly precise, three-dimensional spatially-resolved characterisation of semiconductor detectors. In this work, the TCAD framework Synopsys Sentaurus is used to simulate depth-resolved TPA-TCT data for both p-type pad detectors (PINs) and Low Gain Avalanche Detectors (LGADs). The simulated data are compared against experimentally measured TPA-TCT results. Through this comparison, it is demonstrated that TCAD simulations can reproduce the TPA-TCT measurements, providing valuable insights into the TPA-TCT itself. Another significant outcome of this study is the successful simulation of the gain reduction mechanism, which can be observed in LGADs with increasing densities of excess charge carriers. This effect is demonstrated in an p-type LGAD with a thickness of approximately 286 um. The results confirm the ability of TCAD to model the complex interaction between carrier dynamics and device gain.

physics.ins-det↗