Judith Woerle

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Woerle

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Judith

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0000-0001-6363-0315

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Publications 1 - 10 of 25

Muon Interaction with Negative-U and High-Spin-State Defects: Differentiating between C and Si Vacancies in 4H-SiC
Woerle, Judith; Etzelmüller Bathen, Marianne; Prokscha, Thomas; et al. (2020)
Physical Review Applied
Low-energy muon-spin-rotation spectroscopy (LE-μ SR) is employed to study silicon and carbon vacancies in proton-irradiated 4H-Si C. We show that the implanted muon is quickly attracted to the negative Si vacancy (V Si), where it forms a paramagnetic muonium (Mu0) state, resulting in a reduction of the diamagnetic fraction. In samples with predominantly C vacancies (VC), on the other hand, the formation of Mu0 is very short lived and the muon quickly captures a second electron to form a diamagnetic Mu− state. The results are corroborated by density-functional calculations, where significant differences in the relaxation mechanism of the nearest-neighbor dangling bonds of the vacancies are discussed. We propose that the LE-μ SR technique is capable of differentiating between high-spin and negative-U behavior in semiconducting materials. Finally, our findings emphasize the large potential of LE-μ SR to probe near-surface semiconductor defects, a capability that is crucial for further development of many electronic and quantum technology applications.
Depth-Resolved Study of the SiO2- SiC Interface Using Low-Energy Muon Spin Rotation Spectroscopy
Kumar, Piyush; Martins, Maria Inês M.; Bathen, Marianne; et al. (2022)
Materials Science Forum
In this work, the interface between 4H-SiC and thermally grown SiO2 is studied using low energy muon spin rotation (LE-μSR) spectroscopy. Samples oxidized at 1300 °C were annealed in NO or Ar ambience and the effect of the ambience and the annealing temperature on the near interface region is studied in a depth resolved manner. NO-annealing is expected to passivate the defects, resulting in reduction of interface traps, which is confirmed by electrical characterization. Introduction of N during annealing, to the SiC matrix, results in a thin, carrier rich region close to the interface leading to an increase in the diamagnetic asymmetry. Annealing in an inert environment (Ar) seems to have much lesser impact on the electrical signal, however the μSR shows a reduced paramagnetic asymmetry, indicating a narrow region of low mobility at the interface.
Characterization methods for defects and devices in silicon carbide
Bathen, Marianne; Lew, Christopher T.-K.; Woerle, Judith; et al. (2022)
Journal of Applied Physics
Significant progress has been achieved with silicon carbide (SiC) high power electronics and quantum technologies, both drawing upon the unique properties of this material. In this Perspective, we briefly review some of the main defect characterization techniques that have enabled breakthroughs in these fields. We consider how key data have been collected, interpreted, and used to enhance the application of SiC. Although these fields largely rely on separate techniques, they have similar aims for the material quality and we identify ways in which the electronics and quantum technology fields can further interact for mutual benefit.
Ion Implanted Phosphorous for 4H-SiC VDMOSFETs Source Regions: Effect of the Post Implantation Annealing Time
Nipoti, Roberta; Parisini, Antonella; Boldrini, Virginia; et al. (2020)
Materials Science Forum
Van der Pauw devices have been fabricated by double ion implantation processes, namely P+ and Al+ co-implantation. Similarly to the source area in a SiC VD-MOSFET, a 5 × 1018 cm-3 P plateau is formed on the top of a buried 3 × 1018 cm-3 Al distribution for electrical isolation from the n- epilayer. The post implantation annealing temperature was 1600 °C. Annealing times equal to 30 min and 300 min have been compared. The increase of the annealing time produces both an increase of electron density as well as electron mobility. For comparison a HPSI 4H-SiC wafer, 1×1020 cm-3 P+ ion implanted and 1700 °C annealed for 30 min was also characterized.
Analysis of Thin Thermal Oxides on (0001) SiC Epitaxial Layers
Woerle, Judith; Camarda, Massimo; Schneider, Christof W.; et al. (2016)
Materials Science Forum ~ Silicon Carbide and Related Materials 2016
In this study, electrical properties of MOS capacitors with varying oxide thicknesses have been investigated. The oxide growth was performed at 1050 °C without any further post-oxidation annealing steps resulting in oxide thicknesses between 2 nm and 32 nm. Capacitance-Voltage measurements revealed a decreasing density of interface defects for increasing oxide thickness suggesting a deterioration of the interface at the initial stage of the growth.
4H-SiC(0001) surface faceting during interaction with liquid Si
Soulière, Véronique; Davy, Carole; Camarda, Massimo; et al. (2016)
Materials Science Forum ~ Silicon Carbide and Related Materials 2015
The aim of this study was to find conditions allowing the "natural" formation of a regular and controllable step bunched morphology on a 4H-SiC seed without the need of any SiC deposition. This was performed by melting a bulk piece of Si on a 4°off 4H seed in the temperature range of 1500 - 1600°C, for 15 min. After etching the remaining Si, the 4H surface was found to be successfully highly step bunched with steps very parallel and regular. A mechanism of dissolution-precipitation was proposed, which could occur both on a short (step to step) and long (centre to periphery) range. This process is kinetically limited at low temperature (1500-1550°C) and considered to be close to the equilibrium at 1600°C.
4H-SiC Power VDMOSFET Manufacturing Utilizing POCl3 Post Oxidation Annealing
Ju, Yanrui; Bouvet, Didier; Stark, Roger; et al. (2020)
Materials Science Forum
A novel POCl3 post-oxidation annealing recipe was developed. The interface trap density (Dit) is extracted by the C-ΨS method close to conduction band edge. The performance of the POCl3-treated oxide has been analyzed based on current density-electric field (J-E) measurements. A comprehensive and practical 4H-SiC power VDMOSFET manufacturing traveler has been designed. The power MOSFET that was fabricated based on this traveler exhibits less than half of the on-resistance and shows improved interface characteristics compared to a similarly designed commercial power MOSFET.
Low-Energy Muons as a Tool for a Depth-Resolved Analysis of the SiO2/4H-SiC Interface
Woerle, Judith; Prokscha, Thomas; Grossner, Ulrike (2020)
Materials Science Forum
In this work, the potential of muon spin rotation (μSR) with low-energy muons (LE-μ) for the investigation of oxidation-induced defects at the SiO2/4H-SiC interface is explored. By using implantation energies for the muons in the keV range and comparing the fractions of muonium in different regions, the depth distribution of defects in the first 200 nm of the target material can be resolved. Defect profiles of interfaces with either deposited or thermally grown SiO2 layers on 4H-SiC are compared. The results show an increased number of defects in the case of a thermal oxide, both on the oxide and on the SiC side of the interface, with a spatial extension of a few tens of nm.
Optically active defects at the Si C/Si O2 interface
Johnson, Brett C.; Woerle, Judith; Haasmann, Daniel; et al. (2019)
Physical Review Applied
The SiC/SiO2 interface is a central component of many SiC electronic devices. Defects intrinsic to this interface can have a profound effect on their operation and reliability. It is therefore crucial to both understand the nature of these defects and develop characterization methods to enable optimized SiC-based devices. Here we make use of confocal microscopy to address single SiC/SiO2-related defects and show the technique to be a noncontact, nondestructive, spatially resolved and rapid means of assessing thequality of the SiC/SiO2 interface. This is achieved by a systematic investigation of the defect density of the SiC/SiO2 interface by varying the parameters of a nitric oxide passivation anneal after oxidation. Standard capacitance-based characterization techniques are used to benchmark optical emission rates and densities of the optically active SiC/SiO2-related defects. Further insight into the nature of these defects is provided by low-temperature optical measurements on single defects.
Interaction of low-energy muons with defect profiles in proton-irradiated Si and 4H -SiC
Woerle, Judith; Prokscha, Thomas; Hallén, Anders; et al. (2019)
Physical Review B

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Judith Woerle

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