arXiv subjects

Niels Sorgenfrei

Publications and source records attributed to Niels Sorgenfrei.

5 recordsLinked to original sources

arXiv2025

On the nature and charge state of the X-Defect, a radiation-induced Silicon defect with field-enhanced charge carrier emission

The elusive X-Defect, a defect found in low-resistivity $p$-type Silicon after irradiation, observed as a low-temperature shoulder of the $\mathrm{B}_\mathrm{i}\mathrm{O}_\mathrm{i}$ defect (Boron-interstitial-Oxygen-interstitial complex) in Thermally Stimulated Current (TSC) measurements, was investigated to determine its properties, matching them with those of a previously identified defect. Through a combination of TSC, Deep-Level Transient Spectroscopy (DLTS), Difference-DLTS (DDLTS), numerical simulations of field-enhanced charge carrier emissions in TSC measurements and a comparison to literature, the X-Defect was identified as the singly positively charged Silicon di-vacancy $\mathrm{V}_2(+/0)$. This assignment is supported by an agreement in activation energy, capture cross-section, trap type and charge emission process, as well as simulations comparing the effects of phonon-assisted tunnelling (PAT) and Poole-Frenkel (PF) mechanisms on TSC spectra. DDTLS measurements revealed a quadratic dependence of the activation energy on the electric field strength, confirming PAT as the prevailing mechanism over PF in the case of the radiation-induced X-Defect. Assigning the X-Defect to an electrically neutral defect in the space charge region resolves previous contradictions regarding its deficiency in impacting on the effective doping concentration.

cond-mat.mtrl-sci↗

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

Defects and acceptor removal in 60Co γ-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 γ-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↗

arXiv2024

Characterisation and simulation of stitched CMOS strip sensors

In high-energy physics, there is a need to investigate alternative silicon sensor concepts that offer cost-efficient, large-area coverage. Sensors based on CMOS imaging technology present such a silicon sensor concept for tracking detectors. The CMOS Strips project investigates passive CMOS strip sensors fabricated by LFoundry in a 150nm technology. By employing the technique of stitching, two different strip sensor formats have been realised. The sensor performance is characterised based on measurements at the DESY II Test Beam Facility. The sensor response was simulated utilising Monte Carlo methods and electric fields provided by TCAD device simulations. This study shows that employing the stitching technique does not affect the hit detection efficiency. A first look at the electric field within the sensor and its impact on generated charge carriers is being discussed.

physics.ins-det↗

arXiv2023

Understanding the Frequency Dependence of Capacitance Measurements of Irradiated Silicon Detectors

Capacitance-voltage (CV) measurements are a widely used technique in silicon detector physics. It gives direct information about the full depletion voltage and the effective doping concentration. However, for highly irradiated sensors, the measured data differs significantly from the usual shape which makes the extraction of the afore mentioned parameters less precise to not possible. We present an explanation for the obseved frequency dependence and based on that, a method to extract the desired sensor parameters.

physics.ins-det↗