Niels G. Sorgenfrei

Defect spectroscopy techniques such as Deep-Level Transient Spectroscopy (DLTS) are essential for characterising the electrically active defects that influence the performance of semiconductor materials and sensors, particularly in harsh radiation environments. This work presents a TCAD simulation framework developed to reproduce DLTS spectra. The framework has been applied to several well-known radiation-induced defects in silicon, namely C _i O _i (carbon-interstitial-oxygen-interstitial), B _i O _i (boron-interstitial-oxygen-interstitial), V ₂ (+/0) (single-positive donor charge state of the di-vacancy), and I ₂ O (di-self-interstitial-oxygen-interstitial) using defect parameters (concentration, thermal activation energy, and electron and hole capture cross-sections) extracted either from current (I-DLTS) or capacitance (C-DLTS) transient measurements performed on p -type silicon p-i-n diodes with a bulk resistivity of 250 Ωcm, irradiated to 1 MGy with a ⁶⁰ Co γ-source. Numerical strategies and specific workarounds, such as tuning of mathematical parameters and increasing the charge-carrier generation rate, were implemented to ensure convergence of the TCAD simulations of DLTS measurements down to cryogenic temperatures. To assess the reliability of the framework, two simulation batches were performed, each using one of the two available defect-parameter sets, and the resulting simulated spectra were validated against the measurements.

Gain-layer degradation from exposure to radiation limits the use of Low-Gain Avalanche Diodes (LGADs) in high energy particle physics detector experiments. Proper understanding of how the gain-layer is destroyed is not available on a defect level. Only measurements for materials with much lower effective doping concentrations are available. The direct study of the gain-layer is not possible with typical defect spectroscopy measurements like Thermally Stimulated Currents (TSC) and Deep-Level Transient Spectroscopy (DLTS). To combat this problem and gain a better understanding of the processes which degrade LGADs, the Gain-Layer Project was started. This project produced 19050 diodes with various Boron, Phosphorus, Oxygen and Carbon concentrations. The material used is low-resistivity p-type Silicon. The effective doping concentrations are in the order of a LGAD gain-layer. These diodes will serve the defect community in the coming years for various studies. This article introduces this project with detailed descriptions of the diodes, their flavours and their processing, and reports on results from I-V, C-V, SIMS and DLTS measurements on unirradiated diodes.

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 _1/2 defect and a Nitrogen related defect were identified.