arXiv subjects

Dominic Waldhör

Publications and source records attributed to Dominic Waldhör.

6 recordsLinked to original sources

arXiv2025

Accurate Modeling of Gate Leakage Currents in SiC Power MOSFETs

Silicon carbide (SiC) metal-oxide-semiconductor field-effect-transistors (MOSFETs) enable high-voltage and high-temperature power conversion. Compared to Si devices, they suffer from pronounced gate leakage due to the reduced electron tunneling barrier at the interface between SiC and amorphous silicon dioxide (a-SiO$_2$). We develop a self-consistent, physics-based simulation framework that couples electrostatics, quantum tunneling, carrier transport, impact ionization, and charge trapping for both electrons and holes. The model quantitatively reproduces measured gate-current-voltage characteristics of SiC MOS capacitors over a wide temperature (80-573 K) range and a wide bias range without empirical fitting. Simulations reveal that conduction electrons in a-SiO$_2$ can trigger impact ionization, which generates electron-hole pairs, and leads to capture of holes in the oxide bulk, thereby enhancing gate leakage current. The framework captures these coupled processes across multiple orders of magnitude in time and field, providing predictive capability for oxide reliability. Although demonstrated for SiC devices, the methodology also applies to Si technologies that uses the same gate dielectric.

cond-mat.mtrl-sci↗

arXiv2025

Resonant states and nuclear dynamics in solid-state systems: the case of silicon-hydrogen bond dissociation

Bond breaking in the presence of highly energetic carriers is central to many important phenomena in physics and chemistry, including radiation damage, hot-carrier degradation, activation of dopant-hydrogen complexes in semiconductors, and photocatalysis. Describing these processes from first principles has remained an elusive goal. Here we introduce a comprehensive theoretical framework for the dissociation process, emphasizing the need for a non-adiabatic approach. We benchmark the results for the case of silicon-hydrogen bond dissocation, a primary process for hot-carrier degradation. Passivation of Si dangling bonds by hydrogen is vital in all Si devices because it eliminates electrically active mid-gap states; understanding the mechanism for dissociation of these bonds is therefore crucial for device technology. While the need for a non-adiabatic approach has been previously recognized, explicitly obtaining diabatic states for solid-state systems has been an outstanding challenge. We demonstrate how to obtain these states by applying a partitioning scheme to the Hamiltonian obtained from first-principles density functional theory. Our results demonstrate that bond dissociation can occur when electrons temporarily occupy the antibonding states, generating a highly repulsive excited-state potential that causes the hydrogen nuclear wavepacket to shift and propagate rapidly. Based on the Menzel-Gomer-Redhead (MGR) model, we show that after moving on this excited-state potential on femtosecond timescales, a portion of the nuclear wavepacket can continue to propagate even after the system relaxes back to the ground state, allowing us to determine the dissociation probability. Our results provide essential insights into the fundamental processes that drive carrier-induced bond breaking in general, and specifically elucidate hydrogen-related degradation in Si devices.

cond-mat.mtrl-sci↗

arXiv2024

Machine Learning Force Field for Thermal Oxidation of Silicon

Looking back at seven decades of highly extensive application in the semiconductor industry, silicon and its native oxide SiO$_2$ are still at the heart of several technological developments. Recently, the fabrication of ultra-thin oxide layers has become essential for keeping up with trends in down-scaling of nanoelectronic devices and for the realization of novel device technologies. With this comes a need for better understanding of the atomic configuration at the Si/SiO$_2$ interface. Classical force fields offer flexible application and relatively low computational costs, however, suffer from limited accuracy. Ab-initio methods give much better results but are extremely costly. Machine learning force fields (MLFF) offer the possibility to combine the benefits of both worlds. We train a MLFF for the simulation of the dry thermal oxidation process of a Si substrate. The training data is generated by density functional theory calculations. The obtained structures are in line with ab-initio simulations as well as with experimental observations. Compared to a classical force field, the most recent reactive force field (reaxFF), the resulting configurations are vastly improved.

cond-mat.mtrl-sci↗

arXiv2024

Coherence limit due to hyperfine interaction with nuclei in the barrier material of Si spin qubits

On the quest to understand and reduce environmental noise in Si spin qubits, hyperfine interactions between electron and nuclear spins impose a major challenge. Silicon is a promising host material because one can enhance the spin coherence time by removing spinful $^{29}$Si isotopes. As more experiments rely on isotopic purification of Si, the role of other spinful atoms in the device should be clarified. This is not a straightforward task, as the hyperfine interactions with atoms in the barrier layers are poorly understood. We utilize density functional theory to determine the hyperfine tensors of both Si and Ge in a crystalline epitaxial Si/SiGe quantum well as well as Si and O atoms in an amorphous Si/SiO$_2$ (MOS) interface structure. Based on these results, we estimate the dephasing time $T_2^*$ due to magnetic noise from the spin bath and show that the coherence is limited by interactions with non-Si barrier atoms to a few \textmu s in Si/SiGe (for non-purified Ge) and about 100\,\textmu s in Si-MOS. Expressing these numbers alternatively, in Si/SiGe the interactions with Ge dominate below 1000\,ppm of $^{29}$Si content, and, due to low natural concentration of the spinful oxygen isotopes, the interactions with oxygen in Si-MOS become significant only below 1\,ppm of $^{29}$Si content.

cond-mat.mes-hall↗

arXiv2024

Time-Gated Optical Spectroscopy of Field-Effect Stimulated Recombination via Interfacial Point Defects in Fully-Processed Silicon Carbide Power MOSFETs

Fully-processed SiC power metal-oxide-semiconductor field-effect transistors (MOSFETs) emit light during switching of the gate terminal, while both drain and source terminals are grounded. The emitted photons are caused by defect-assisted recombination of electrons and holes at the 4H-SiC/SiO$_2$ interface and can be detected through the SiC substrate. Here, we present time-gated spectroscopic characterization of these interfacial point defects. Unlike in previous studies, the devices were opened in such a way that the drain-contact remained electrically active. A separate examination of the photons emitted at the rising and falling transitions of the gate-source voltage enabled the extraction of two different spectral components. One of these components consists of a single transition with phonon replicas of a local vibrational mode (LVM) with an astonishingly high energy of 220 meV $\unicode{x2013}$ well above the highest phonon modes in 4H-SiC and SiO$_2$ of 120 meV and 137 meV, respectively. Based on a quantum mechanical model, we successfully fitted its emission spectrum and assigned it to donor-acceptor pair recombination involving a carbon cluster-like defect. Other transitions were assigned to EH$_{6/7}$-assisted, EK$_2$-D, and nitrogen-aluminum donor-acceptor pair recombination. Due to the relevance of these defects in the operation of SiC MOSFETs, these novel insights will contribute to improved reliability and performance of these devices.

physics.app-ph↗

arXiv2022

Modeling the Initial Stages of Si(100) Thermal Oxidation: An Ab-initio Approach

Silicon together with its native oxide SiO$_2$ was recognized as an outstanding material system for the semiconductor industry in the 1950s. In state-of-the-art device technology, SiO$_2$ is widely used as an insulator in combination with high-$k$ dielectrics such as HfO$_2$, demanding fabrication of ultra-thin interfacial layers. The classical standard model derived by Deal and Grove accurately describes the oxidation of Si in a progressed stage, however, strongly underestimates growth rates for thin oxide layers. Recent studies report a variety of oxidation mechanisms during the growth of oxide films in the range of \SI{10}{\angstrom} with various details still under debate. This paper presents a first-principles based approach to theoretically assess the thermal oxidation process of the technologically relevant Si(100) surfaceduring this initial stage. Our investigations range from the chemisorption of single O$_2$ molecules onto the $p(2\times2)$ reconstructed Si surface to oxidized Si surface layers with a thickness of up to \SI{20}{\angstrom}. The initially observed enhanced growth rate is assigned to barrierless O$_2$ chemisorption events upon which the oxygen molecule dissociate. We present strong evidence for an immediate amorphization of the oxide layer from the onset of oxidation. Surface reactions dominate until the surface is saturated with oxygen and separated from the Si substrate by a \SI{5}{\angstrom} transition region. The saturated surface becomes inert to dissociative reactions and enables the diffusion of molecular oxygen to the \interface interface as assumed within the Deal-Grove model. Further oxidation of the Si substrate is then provided by O$_2$ dissociations at the interface due to the same charge transfer process responsible for the chemisorption at the surface.

cond-mat.mtrl-sci↗