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## Publications

Publications (154)

Controlling single-electron states becomes increasingly important due to the wide-ranging advances in electron quantum optics. Single-electron control enables coherent manipulation of individual electrons and the ability to exploit the wave...

The widespread Wigner formulation of quantum mechanics is obtained with the help of the Weyl transform of the density matrix and the corresponding von Neumann equation formulated in terms of scalar potentials only. To obtain a gauge-invariant Wigner theory in an electromagnetic field, one can apply a Weyl-Stratonovich transform to remove the vector...

This special issue contains four contributions from leading groups presenting state-of-the-art modeling and simulation of future classical logic and memory devices, which utilize various quantum concepts for their operation. During the past twenty years quantum engineering of classical devices has been mainly responsible for fueling Moore's Law for...

Fluorocarbon dry etching of vertical silica-based structures is essential to the fabrication of advanced complementary metal-oxide-semiconductor and dynamic random access memory devices. However, the development of etching technology is challenged by the lack of understanding of complex surface reaction mechanisms and by the intricacy of etchant fl...

The level-set method is widely used in expanding front simulations in numerous fields of computational research, such as computer graphics, physics, or microelectronics. In the latter, the level-set method is employed for topography simulations of semiconductor device fabrication processes, being driven by complicated physical and chemical models....

Atomic layer deposition allows for precise control over film thickness and conformality. It is a critical enabler of high aspect ratio structures, such as 3D NAND memory, since its self-limiting behavior enables higher conformality than conventional processes. However, as the aspect ratio increases, deviations from complete conformality frequently...

A gauge-invariant Wigner quantum mechanical theory is obtained by applying the Weyl-Stratonovich transform to the von Neumann equation for the density matrix. The transform reduces to the Weyl transform in the electrostatic limit, when the vector potential and thus the magnetic field are zero. Both cases involve a center-of-mass transform followed...

Thin material layers are common structures in modern semiconductor device fabrication and are particularly necessary for light-emitting diodes and three-dimensional NAND memory devices. Such layers are not only deposited on the flat wafer surface but are also partially removed during subsequent etching steps. Level-set based process TCAD simulation...

Atomic layer deposition allows for precise control over film thickness and conformality. It is a critical enabler of high aspect ratio structures, such as 3D NAND memory, since its self-limiting behavior enables higher conformality than conventional processes. However, as the aspect ratio increases, deviations from ideal conformality frequently occ...

Inspired by using the wave nature of electrons for electron quantum optics, we propose a new type of electron quantum interference structure, where single-electron waves are coherently injected into a gate-controlled, two-dimensional waveguide and exit through one or more output channels. The gate-controlled interference effects lead to specific cu...

A gauge-invariant Wigner quantum mechanical theory is obtained by applying the Weyl-Stratonovich transform to the von Neumann equation for the density matrix. The transform reduces to the Weyl transform in the electrostatic limit, when the vector potential and thus the magnetic field are zero. Both cases involve a center-of-mass transform followed...

Confinement in small structures has required quantum mechanics, which has been known for a great many years. This leads to quantum transport. The field-effect transistor has had no need to be described by quantum transport over most of the century for which it has existed. But, this has changed in the past few decades, as modern versions tend to be...

Quantum electronics has significantly evolved over the last decades. Where initially the clear focus was on light-matter interactions, nowadays approaches based on the electron's wave nature have solidified themselves as additional focus areas. This development is largely driven by continuous advances in electron quantum optics, electron based quan...

Low-bias etching of silicon (Si) using sulfur hexafluoride (SF6) plasma is a valuable tool in the manufacturing of electronic devices and micro electro-mechanical systems (MEMS). This kind of etching offers an almost isotropic etching behaviour, since the low voltage bias does not provide enough vertical acceleration and kinetic energy to the ions....

We present a feature detection method for adaptive grid refinement in hierarchical grids used in process technology computer-aided design topography simulations based on the local curvature of the wafer surface. The proposed feature detection method enables high-accuracy simulations whilst significantly reducing the run-time, because the grid is on...

The level-set method is widely used for high-accuracy 3-D topography simulations in process technology computer-aided design (TCAD) because of its robustness to topological changes introduced by the involved complicated physical phenomena. Particularly challenging are material flow processes, such as oxidation, reflow, and silicidation, as these re...

Entangled quantum particles, in which operating on one particle instantaneously influences the state of the entangled particle, are attractive options for carrying quantum information at the nanoscale. However, fully-describing entanglement in traditional time-dependent quantum transport simulation approaches requires significant computational effo...

Recent advances in electron quantum optics show the breathtaking progress in utilizing the electron's wave nature. Inspired by these advances, we propose a new type of electron quantum interference logic device (eQILD), where an electron wave is coherently injected into a two-dimensional (2D) wave guide and controlled via two gates. Interference ef...

Inspired by using the wave nature of electrons for electron quantum optics, we propose a new type of electron quantum interference logic device (eQILD), where an electron wave is coherently injected into a two-dimensional wave guide and controlled via two gates. Interference effects lead to different current levels in output channels and are utiliz...

Inspired by using the wave nature of electrons for electron
quantum optics, we propose a new type of electron quantum
interference structure, where single-electron waves are coherently
injected into a gate-controlled, two-dimensional waveguide and
exit through one or more output channels. The thus gatecontrolled
interference effects lead to specifi...

We present a continuum modeling approach to simulate anisotropic wet etching of single-crystal sapphire employing mixtures of sulfuric acid and phosphoric acid. Wet etching of sapphire leads to the formation of crystal facets with high Miller–Bravais indices. The resulting complex three-dimensional topographies can be exploited to optimize the patt...

The fast marching method is commonly used in expanding front simulations in various fields, such as, fluid dynamics, computer graphics, and in microelectronics, to restore the signed-distance field property of the level-set function, also known as re-distancing. To improve the performance of the re-distancing step, parallel algorithms for the fast...

Topography simulation is typically implemented with the level-set method which uses the level-set function to represent the interface. The signed-distance property, capturing the distances from the entire simulation domain towards the interface, has to be regularly restored during a simulation in order to update the distances relative to the evolut...

In etching and deposition simulations of a semiconductor fabrication process the calculation of the surface rates of particles is an essential but also the computationally most demanding step. A promising approach is to preprocess the simulation domain by simplifying the surface. We thus propose a new surface mesh simplification method that takes a...

The continued reduction of semiconductor device feature sizes towards the single-digit nanometer regime involves a variety of quantum effects. Modeling quantum effects in phase space in terms of the Wigner transport equation has evolved to be a very effective approach to describe such scaled down complex systems, accounting from full quantum proces...

We present numerical methods to enable accurate and robust level-set based simulation of anisotropic wet etching and non-planar epitaxy for semiconductor fabrication. These fabrication techniques are characterized by highly crystal orientation-dependent etch/growth rates, which lead to non-convex Hamiltonians in their description by the level-set e...

The level-set method is widely used to track the motion of interfaces driven by a velocity field. In many applications, the underlying physical model defines the velocity field only at the interface itself. For these applications, an extension of the velocity field to the simulation domain is required. This extension has to be performed in each tim...

A common problem arising in expanding front simulations is to restore the signed distance field property of a discretized domain (i.e., a mesh), by calculating the minimum distance of mesh points to an interface. This problem is referred to as re-distancing and a widely used method for its solution is the fast marching method (FMM). In many cases,...

Step-controlled growth of 4H-SiC epitaxial layers leads to the formation of a step-bunched morphology along the surface with larger macrosteps, composed of smaller microsteps of several Si-C bilayer heights. As thermal oxidation is an orientation-dependent process, a multi-faceted surface is expected to exhibit a different oxidation behavior compar...

Numerical simulation is an important tool used in various fields of computational science and engineering. The models to be solved by simulation are predominantly based on equations which require the discretization of a spatial domain. The accuracy of the simulation results is heavily influenced by the properties of the underlying spatial discretiz...

Technological control of doped regions is exceptionally important for all semiconductor devices. For the wide bandgap semiconductor silicon carbide, the activation state of dopants is determined by the postimplantation annealing step which consequently affects device operation and characteristics. We perform a detailed analysis of the effects of po...

Manufacturing integrated circuits was never a simple process. However, with scaling slowing down more significantly in the single digit nanometer regime due to skyrocketing fabrication costs the need
for comparatively cheap simulation-based predictions has further increased. However, the necessary simulation tools in electronics and specifically in...

Quantum information and quantum communication are both strongly based on concepts of quantum superposition and entanglement. Entanglement allows distinct bodies, that share a common origin or that have interacted in the past, to continue to be described by the same wave function until evolution is coherent. So, there is an equivalence between coher...

Process technology computer-aided design (TCAD) deals with simulating semiconductor device fabrication steps, such as etching and deposition, to enable computer-based device designs. The simulation backends are based on a variety of numerical methods, e.g., particle transport, surface advection, diffusion, and stress calculation, underlining the in...

Gauge-invariant Wigner theories are formulated in terms of the kinetic momentum, which—being a physical quantity—is conserved after a change of the gauge. These theories rely on a transform of the density matrix, originally introduced by Stratonovich, which generalizes the Weyl transform by involving the vector potential. We thus present an alterna...

Among the many application areas of graphs is modeling of irregular data structures in various problems occurring in linear algebra, preconditioners, community detection, scheduling, and mesh adaptation. Within the scope of computational science and engineering, the standard graph coloring problem, the distance-1 coloring, is typically used to sele...

The Wigner function was formulated in 1932 by Eugene Paul Wigner, at a time when quantum mechanics was in its infancy. In doing so, he brought phase space representations into quantum mechanics. However, its unique nature also made it very interesting for classical approaches and for identifying the deviations from classical behavior and the entang...

We present an analysis of the quantum processes involved in the electron evolution around a repulsive dopant in a quantum wire. The quantum electron behavior has been studied by using a Wigner function approach. The Wigner phase space description allows to treat both classical and quantum evolution in the same framework, enabling to easily highligh...

The ongoing miniaturization in electronics poses various challenges in the designing of modern devices and also in the development and optimization of the corresponding fabrication processes. Computer simulations offer a cost- and time-saving possibility to investigate and optimize these fabrication processes. However, modern device designs require...

Among the many application areas of graphs is modeling of irregular data structures in various problems occurring in linear algebra, preconditioners, community detection, scheduling, and mesh adaptation. Within the scope of computational science and engineering, the standard graph coloring problem, the distance-1 coloring, is typically used to sele...

The development of novel electron devices requires a continuous support by process and device simulations in order to improve electrical properties and reduce production costs. However, an accurate description of the electrical properties of impurities in silicon carbide – a key wide bandgap semiconductor for power devices – is currently not availa...

A time-dependent modeling approach for electrical activation of implanted dopant species in semiconductors is currently missing, which limits the predictability of process simulations in technology computer-aided design. In this study we investigate the time-dependent electrical activation of phosphorus-implanted silicon carbide and propose a trans...

We focus on a surface evolution problem where the local surface speed depends on a computationally expensive scalar function with non-local properties. The local surface speed must be re-evaluated in each time step, even for non-moving parts of the surface, due to possibly changed properties in remote regions of the simulation domain. We present a...

We propose an empirical model to predict electrical activation ratios of aluminium- and boron-implanted silicon carbide with respect to various annealing temperatures. The obtained parameters and model extensions are implemented into Silvaco’s Victory Process simulator to enable accurate predictions of post-implantation process steps. The thus augm...

The advent of modern many- and multi-core architectures offers the option of utilizing parallel computing to reduce the overall runtime of applications. An attractive option is to decompose a computational task into independent sets, which enables independent parallel processing, i.e., without computational dependencies which potentially limit para...

Herein, an analysis of interference effects as a result of the electron evolution within a coherent transport medium is presented, offering a double‐dopant Coulomb potential structure. Injection of coherent electron states into the structure is used to investigate the effects on the current transport behavior within the quantum Wigner phase space p...

We present a signed particle computational approach for the Wigner transport model and use it to analyze the electron state dynamics in quantum wires focusing on the effect of surface roughness. Usually surface roughness is considered as a scattering model, accounted for by the Fermi Golden Rule, which relies on approximations like statistical aver...

Accurate modeling of the electrical properties of impurities in semiconductors is essential for the mandatory support of the development of novel semiconductor devices by means of simulations. An appropriate modeling approach to determine the activation rate of dopants in silicon carbide is currently not available, which limits the predictability o...

We focus on a surface evolution problem where the surface is represented as a narrow-band level-set and the local surface speed is defined by a relation to the direct visibility of a source plane above the surface. A level-set representation of the surface can handle complex evolutions robustly and is therefore a frequently encountered choice. Ray...

We analyze the early stage of the highly-anisotropic silicon carbide oxidation behaviour with reactive force field molecular dynamics simulations. The oxidation of a-, C,- m-, and Si-crystallographic faces is studied at typical industry-focused temperatures in the range from 900 to 1200°C, based on the time evolution of the oxidation mechanism. The...

- A modeling approach for the electrical activation of implanted species in silicon carbide (SiC) is currently missing, which limits the predictability of process simulations. - We propose an empirical model to predict electrical activation ratios of aluminium (Al) and boron (B) implanted SiC. - The obtained parameters and model extensions are impl...

Typical p-type doping species in silicon carbide (SiC) are aluminium (Al) and boron (B), which are commonly implanted into the semiconductor. In order to increase the electrical activation of the implanted species, it is extremely important to perform thermal annealing as a post-implantation step. We have therefore investigated the post-implantatio...

- A modeling approach for the electrical activation of implanted species in silicon carbide (SiC) is currently missing, which limits the predictability of process simulations. - We propose an empirical model to predict electrical activation ratios of aluminium (Al) and boron (B) implanted SiC. - The obtained parameters and model extensions are impl...

We propose an empirical model to predict electrical activation ratios of aluminium- and boron-implanted silicon carbide with respect to various annealing temperatures. The obtained parameters and model extensions are implemented into Silvaco’s Victory Process simulator to enable accurate predictions of post-implantation process steps. The thus augm...

We propose an empirical model to accurately predict electrical activation ratios of phosphorus and nitrogen implanted silicon carbide for arbitrary annealing temperatures. We introduce model parameters and compare the activation behaviour of the two donor-type dopants. Our investigations show that the activation ratio of the nitrogen implanted sili...

We present a flexible coarse-grained shared-memory parallel mesh adaptation approach based on graph partitioning and graph coloring. The strength of our approach is the ability to use existing serial meshing algorithms for the overall parallel meshing workflow. Our approach does not require a fine-grained parallel meshing algorithm and thus reduces...

We present a Wigner signed particles analysis of the lense-governed electron state dynamics based on the quantitative theory of coherence reformulated in phase space terms. Electrostatic lenses are used for manipulating electron evolution and are therefore attractive for applications in novel engineering disciplines like entangletronics. The signed...

We present a Wigner signed particles analysis of the lense-governed electron state dynamics based on the quantitative theory of coherence reformulated in phase space terms. Electrostatic lenses are used for manipulating electron evolution and are therefore attractive for applications in novel engineering disciplines like entangletronics. The signed...

In numerical simulations of various areas of science and engineering, e.g., biomechanical engineering or ray tracing, the discretization of objects in physical space is an integral step. In particular for three-dimensional cases, where a volume mesh generation is required, the mesh generation is rather critical for the robustness, stability, and ac...

This is the 25th special symposium devoted to the impact of high performance computing and communications on computer simulations. The symposium encompasses a wide variety of topics with a focus on tools and applications for the simulation of physical and engineering systems.

Semiconductor process simulation enables to predict critical manufacturing steps of
semiconductor devices and circuits. In particular, it allows for so-called structure prototyping used in the critical exploratory phases of new semiconductor technologies. The ever-ongoing reduction of feature sizes and the required move towards increasingly intric...