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For semiconductor device fabrication, Pulsed Laser Annealing (PLA) offers significant advantages over conventional thermal processes. Notably, it can provide ultrafast (~ns) and high temperature profiles ($>1000^\circ$C). When the maximum temperature exceeds the melting point, a solid-liquid phase transition is observed, immediately followed by rapid recrystallization. This unique annealing mechanism gives raises questions about dopant diffusion and residual defects, in not only in the recrystallized region, but also just below it. As power devices require micrometer-sized junctions, high laser energy densities are needed, which were proved to promote the incorporation of complex impurities from the surface and the creation of defects at the liquid/solid interface. This paper reports on the impact of laser annealing at high energy densities (up to 8.0 J/cm$^2$) on the leakage current, using Schottky and PN diodes, and DLTS measurements. Various laser annealing conditions were used: energy densities between 1.7 and 8.0 J/cm$^2$ with 1 to 10 pulses. Our results suggest that the liquid and solid solubility of vacancies in silicon are fixed by the maximum temperature reached, so to the energy density. Increasing the number of laser pulses allows, not only to reach this maximum vacancy concentration but also to promote their diffusion towards the surface. Concomitantly, the in-diffusion of complex impurities inside the melted region allows the coupling between both defect types to create trap centers, responsible for the degradation of the leakage current.

Ultraviolet nanosecond laser annealing (UV-NLA) proves to be an important technique, particularly when tightly controlled heating and melting are necessary. In the realm of semiconductor technologies, the significance of nanosecond laser annealing (NLA) grows in tandem with the escalating intricacy of integration schemes in nano-scaled devices. Silicon-germanium alloys have been studied for decades for their compatibility with silicon devices. Indeed, they enable the manipulation of properties like strain, carrier mobilities and bandgap. In this framework, they can for instance boost the performances of p-type MOSFETs but also enable near infra-red absorption and emission for applications in photo-detection and photonics. Laser melting on such type of layers, however results, up to now, in the development of extended defects and poor control over layer morphology and homogeneity. In our study, we investigate the laser melting of ~700 nm thick relaxed silicon-germanium samples coated with SiO2 nano-arrays, observing the resulting material to maintain an unaltered lattice. We found the geometrical parameters of the silicon oxide having an impact on the thermal budget samples see, influencing melt threshold, melt depth and germanium distribution.

Correlated errors caused by ionizing radiation impacting superconducting qubit chips are problematic for quantum error correction. Such impacts generate quasiparticle (QP) excitations in the qubit electrodes, which temporarily reduce qubit coherence significantly. The many energetic phonons produced by a particle impact travel efficiently throughout the device substrate and generate quasiparticles with high probability, thus causing errors on a large fraction of the qubits in an array simultaneously. We describe a comprehensive strategy for the numerical simulation of the phonon and quasiparticle dynamics in the aftermath of an impact. We compare the simulations with experimental measurements of phonon-mediated QP poisoning and demonstrate that our modeling captures the spatial and temporal footprint of the QP poisoning for various configurations of phonon downconversion structures. We thus present a path forward for the operation of superconducting quantum processors in the presence of ionizing radiation., Comment: 18 pages, 15 figures, 2 tables

Networks of Rydberg atoms provide a powerful basis for quantum simulators and quantum technologies. Inspired by matter-wave atomtronics, here we engineer switches, diodes and universal logic gates. Our schemes control the Rydberg excitation dynamics via the anti-blockade or facilitation mechanism, allowing for much faster devices compared to cold atom systems. Our approach is robust to noise and can be applied to individually trapped atoms and extensive three-dimensional gases. In analogy to electronics, Rydberg atomtronic devices promise to enhance quantum information processors and quantum simulators.

The properties of liquid Si-Ge binary systems at melting conditions deviate from those expected by the ideal alloy approximation. Particularly, a non-linear dependence of the dielectric functions occurs with the reflectivity of liquid Si-Ge reaching a maximum at 50\% Ge content, being 10\% higher than in pure Si or Ge. Using \textit{ab initio} methodologies, we modelled liquefied Si-Ge alloys, unveiling very high coordination numbers and poor symmetry in the first coordination shell with respect to Si and Ge, related to different bonding properties. We simulated optical functions, quantitatively replicating the aforementioned reflectivity trend and we highlighted a direct relationship between atomic structure and optical properties, indicating that the unusual optics arises from Si-Ge higher local coordination characterized by low symmetry. We forecast further implications for the overall class of these alloys. These findings expand our comprehension of liquefied semiconductors and are essential for implementing controlled laser melting procedures to highly dope these materials for advanced transistors, superconductors, sensors and plasmonic devices.

Controlling ultrafast material transformations with atomic precision is essential for future nanotechnology. Pulsed laser annealing (LA), inducing extremely rapid and localized phase transitions, is a powerful way to achieve this, but it requires careful optimization together with the appropriate system design. We present a multiscale LA computational framework able to simulate atom-by-atom the highly out-of-equilibrium kinetics of a material as it interacts with the laser, including effects of structural disorder. By seamlessly coupling a macroscale continuum solver to a nanoscale super-lattice Kinetic Monte Carlo code, this method overcomes the limits of state-of-the-art continuum-based tools. We exploit it to investigate nontrivial changes in composition, morphology and quality of laser-annealed SiGe alloys. Validations against experiments and phase-field simulations, as well as advanced applications to strained, defected, nanostructured and confined SiGe are presented, highlighting the importance of a multiscale atomistic-continuum approach. Current applicability and potential generalization routes are finally discussed.

In this paper, the atomic layer deposition (ALD) of ultra-thin films (<4 nm) of $Al_{2}O_{3}$ and $HfO_{2}$ on Au-supported monolayer (1L) $MoS_{2}$ is investigated, providing an insight on the nucleation mechanisms in the early stages of the ALD process. A preliminary multiscale characterization of large area 1L-$MoS_{2}$ exfoliated on sputter-grown Au/Ni films revealed an almost conformal $MoS_{2}$ membrane with the Au topography and the occurrence of strain variations at the nanoscale. Ab-initio DFT calculations of $MoS_{2}$/Au(111) interface showed a significant influence of the Au substrate on the $MoS_{2}$ energy band structure, whereas small differences were accounted for the adsorption of the $H_{2}O$, TMA and TDMAHf precursors. This suggests a crucial role of nanoscale morphological effects, such as local curvature and strain of the $MoS_{2}$ membrane, in the enhanced physisorption of the precursors. Therefore, the nucleation and growth of $Al_{2}O_{3}$ and $HfO_{2}$ films onto 1L-$MoS_{2}$/Au was investigated, by monitoring the surface coverage as a function of the number (N) of ALD cycles, with N from 10 to 120. At low N values, a slower growth rate of the initially formed nuclei was observed for $HfO_{2}$, probably due to the bulky nature of the TDMAHf precursor as compared to TMA. On the other hand, the formation of continuous films was obtained in both cases for N>80 ALD cycles, corresponding to 3.6 nm $Al_{2}O_{3}$ and 3.1 nm $HfO_{2}$. Current mapping by C-AFM showed, for the same applied bias, a uniform insulating behavior of $Al_{2}O_{3}$ and the occurrence of few localized breakdown spots in the case of $HfO_{2}$, associated to less compact films regions. Finally, an increase of the 1L-$MoS_{2}$ tensile strain was observed by Raman mapping after encapsulation with both high-k films, accompanied by a reduction in the PL intensity., Comment: 26 pages, 9 figures

Ultraviolet nanosecond laser annealing (LA) is a powerful tool where strongly confined heating and melting are desirable. In semiconductor technologies the importance of LA increases with the increasing complexity of the proposed integration schemes. Optimizing the LA process along with the experimental design is challenging, especially when complex 3D nanostructured systems with various shapes and phases are involved. Within this context, reliable simulations of laser melting are required for optimizing the process parameters while reducing the number of experimental tests. This gives rise to a virtual Design of Experiments (DoE). $Si_{1-x}Ge_{x}$ alloys are nowadays used for their compatibility with silicon devices enabling to engineer properties such as strain, carrier mobilities and bandgap. In this work, the laser melting process of relaxed and strained $Si_{1-x}Ge_{x}$ is simulated with a finite element method / phase field approach. Particularly, we calibrated the dielectric functions of the alloy for its crystalline and liquid phase using experimental data. We highlighted the importance of reproducing the exact reflectivity of the interface between air and the material in its different aggregation states, to correctly mimic the process. We indirectly discovered intriguing features on the optical behavior of melt silicon-germanium.

We study the silicon vacancy in 3C SiC as a color center of interest in the field of Quantum Technologies, focusing on its magnetic interaction with the SiC nuclear spin bath containing Si29 and C13 nuclei in their natural isotopic concentration. We calculate the system energetic and magnetic properties with ab initio methods based on the Density Functional Theory, identifying the neutral charge state of the silicon vacancy as the most favorable for p doped 3C SiC systems. We thereon evaluate the Free Induction Decay and the Hahn echo sequence on the electron spin interacting with the nuclear spin bath. Here, the Electron Spin Echo Envelope Modulation phenomenon, due to single nuclear spin flipping processes, and the overall decay are highlighted in the context of the Cluster Correlation Expansion theory. We find a non exponential coherence decay, which is a typical feature of solid state qubits subjected to low frequency 1/f noise from the environment., Comment: 36 pages, 10 figures, 3 tables

Low-power SRAM architectures are especially sensitive to many types of defects that may occur during manufacturing. Among these, resistive defects can appear. This paper analyzes some types of such defects that may impair the device functionalities in subtle ways, depending on the defect characteristics, and that may not be directly or easily detectable by traditional test methods, such as March algorithms. We analyze different methods to test such defects and discuss them in terms of complexity and test time., Comment: Paper accepted and presented in The 22nd IEEE Latin-American Test Symposium (LATS 2021) October 27 - 29, 2021, Brazil. It is going to be published in the IEEExplorer. 6 pages, 7 figures, 3 tables

We propose a two-stage multi-objective optimization framework for full scheme solar cell structure design and characterization, cost minimization and quantum efficiency maximization. We evaluated structures of 15 different cell designs simulated by varying material types and photodiode doping strategies. At first, non-dominated sorting genetic algorithm~II (NSGA-II) produced Pareto-optimal-solutions sets for respective cell designs. Then, on investigating quantum efficiencies of all cell designs produced by NSGA-II, we applied a new multi-objective optimization algorithm~II (OptIA-II) to discover the Pareto fronts of select (three) best cell designs. Our designed OptIA-II algorithm improved the quantum efficiencies of all select cell designs and reduced their fabrication costs. We observed that the cell design comprising an optimally doped zinc-oxide-based transparent conductive oxide (TCO) layer and rough silver back reflector (BR) offered a quantum efficiency ($Q_e$) of $0.6031.$ Overall, this paper provides a full characterization of cell structure designs. It derives a relationship between quantum efficiency, $Q_e$ of a cell with its TCO layer's doping methods and TCO and BR layer's material types. Our solar cells design characterization enables us to perform a cost-benefit analysis of solar cells usage in real-world applications, Comment: published in 2021

The electrical behavior of Ni Schottky barrier formed onto heavily doped (ND>1019 cm-3) n-type phosphorous implanted silicon carbide (4H-SiC) was investigated, with a focus on the current transport mechanisms in both forward and reverse bias. The forward current-voltage characterization of Schottky diodes showed that the predominant current transport is a thermionic-field emission mechanism. On the other hand, the reverse bias characteristics could not be described by a unique mechanism. In fact, under moderate reverse bias, implantation-induced damage is responsible for the temperature increase of the leakage current, while a pure field emission mechanism is approached with bias increasing. The potential application of metal/4H-SiC contacts on heavily doped layers in real devices are discussed.

We investigated the complex interaction between a nickel layer and a 4H-SiC substrate under UV-laser irradiation since the early stages of the atomic inter-diffusion. An exhaustive description is still lacking in the literature. A multimethod approach based on Transmission Electron Microscopy, Energy Dispersive Spectroscopy and Diffraction (electron and X-ray) techniques has been implemented for a cross-correlated description of the final state of the contact after laser irradiation. They detailed the stoichiometry and the lattice structure of each phase formed as well as the Ni/Si alloy profile along the contact for laser fluences in the range 2.4-3.8 J/cm2. To make a bridge between process conditions and post-process characterizations, time dependent ultra-fast phenomena (laser pulse about 160ns), such as intermixing driven melting and Ni-silicides reactions, have been simulated by a modified phase fields approach in the proper many-compounds formulation. We disclose that raising laser fluence has multiple effects: 1) the thickness of the silicide layer formed at the interface with 4H-SiC expands; 2) the silicon content into the reacted layer increases; 3) a Ni2Si phase is promoted at the highest fluence 3.8 J/cm2; 4) silicon atomic diffusion into a topmost residual nickel layer occurs, with the Ni/Si ratio increasing towards the contact surface., Comment: 12 pages, 8 figures

We present a stochastic simulation method designed to study at an atomic resolution the growth kinetics of compounds characterized by the sp3-type bonding symmetry. Formalization and implementation details are discussed for the particular case of the 3C-SiC material. A key feature of our numerical tool is the ability to simulate the evolution of both point-like and extended defects, whereas atom kinetics depend critically on process-related parameters. In particular, the simulations can describe the surface state of the crystal and the generation/evolution of defects as a function of the initial substrate condition and the calibration of the simulation parameters. We demonstrate that quantitative predictions of the microstructural evolution of the studied systems can be readily compared with the structural characterization of actual processed samples.

Studying the electrical and structural properties of the interface of the gate oxide (SiO2) with silicon carbide (4H-SiC) is a fundamental topic, with important implications for understanding and optimizing the performances of metal-oxide-semiconductor field effect transistor (MOSFETs). In this paper, near interface oxide traps (NIOTs) in lateral 4H-SiC MOSFETs were investigated combining transient gate capacitance measurements (C-t) and state of the art scanning transmission electron microscopy in electron energy loss spectroscopy (STEM-EELS) with sub-nm resolution. The C-t measurements as a function of temperature indicated that the effective NIOTs discharge time is temperature independent and electrons from NIOTs are emitted toward the semiconductor via-tunnelling. The NIOTs discharge time was modelled taking into account also the interface state density in a tunnelling relaxation model and it allowed to locate traps within a tunnelling distance up to 1.3nm from the SiO2/4H-SiC interface. On the other hand, sub-nm resolution STEM-EELS revealed the presence of a Non-Abrupt (NA) SiO2/4H-SiC interface. The NA interface shows the re-arrangement of the carbon atoms in a sub-stoichiometric SiOx matrix. A mixed sp2/sp3 carbon hybridization in the NA interface region suggests that the interfacial carbon atoms have lost their tetrahedral SiC coordination.

In spite of its great promises for energy efficient power conversion, the electronic quality of cubic silicon carbide (3C-SiC) on silicon is currently limited by the presence of a variety of extended defects in the heteroepitaxial material. However, the specific role of the different defects on the electronic transport is still under debate. In this work, a macro- and nano-scale characterization of Schottky contacts on 3C-SiC/Si was carried out, to elucidate the impact of the anti-phase-boundaries (APBs) and stacking-faults (SFs) on the forward and reverse current-voltage characteristics of these devices. Current mapping of 3C-SiC by conductive atomic force microscopy (CAFM) directly showed the role of APBs as the main defects responsible of the reverse bias leakage, while both APBs and SFs were shown to work as preferential current paths under forward polarization. Distinct differences between these two kinds of defects were also confirmed by electronic transport simulations of a front-to-back contacted SF and APB. These experimental and simulation results provide a picture of the role played by different types of extended defects on the electrical transport in vertical or quasi-vertical devices based on 3C-SiC/Si, and can serve as a guide for improving material quality by defects engineering., Comment: 20 pages, 7 figures

We study coherent backscattering phenomena from single and multiple stacking faults (SFs) in 3C- and 4H-SiC within density functional theory quantum transport calculations. We show that SFs give rise to highly dispersive bands within both the valance and conduction bands that can be distinguished for their enhanced density of states at particular wave number subspaces. The consequent localized perturbation potential significantly scatters the propagating electron waves and strongly increases the resistance for $n$-doped systems. We argue that resonant scattering from SFs should be one of the principal degrading mechanisms for device operation in silicon carbide., Comment: 5 pages, 4 figures

In this article we develop an analytical theory that correlates the macroscopic curvature of stressed film/substrate systems with the microscopic in-plane and out-of-plane deflections of planar rotators. Extending this stress-deflection relations in the case of nonlinear stress fields and validating the results with the aid of finite element simulations. We use this theory to study the heteroepitaxial growth of cubic silicon carbide on silicon (100) and discover that due, to defects generated on the silicon substrate during the carbonization process, wafer curvature techniques may not allow the determination of the stress field in the grown films either quantitatively or qualitatively.

We present an orbital-resolved density functional theory study on the electronic properties of hydrogen and lithium intercalated graphene grown on the Si face of SiC. Starting from the $(6\sqrt3\times6\sqrt3)R30^{\circ}$ surface reconstruction of the graphene/SiC heterosystem, we find that both H and Li can restore the ideal structural characteristics of the two nonequivalent junction parts (i.e. graphene and the SiC substrate) when inserted at the interface. However, the chemical/electrostatic interactions remain different for the two cases. Hence, H-intercalated epitaxial graphene is subject to a sublattice symmetry-breaking electronic interference that perturbs the Dirac point, whereas Li intercalation gives rise to a highly $n$-doped system due to a nonuniform delocalization of Li charges. Results bring to discussion the role of substrate engineering in epitaxial graphene on SiC., Comment: 6 pages, 4 figures, accepted in PRB

We perform density functional theory calculations for the determination of the structural and electronic properties of epitaxial graphene on 4H-SiC(000$\bar{1}$). Using commensurate supercells that minimize non-physical stresses we show that, in contrast with Si-face epitaxial films, the first graphene layer that forms on the C-face of SiC is purely metallic with its $\pi$-bands partially preserved. Typical free-standing characteristics are fully recovered with a second graphene layer. We moreover discuss on the magnetic properties of the interface and the absence of Fermi-level pinning effects that could allow for a plausible device operation starting from the off-state., Comment: 4 pages, 4 figures

We calculate quantum transport for metal-graphene nanoribbon heterojunctions within the atomistic self-consistent Schr\"odinger/Poisson scheme. Attention is paid on both the chemical aspects of the interface bonding as well the one-dimensional electrostatics along the ribbon length. Band-bending and doping effects strongly influence the transport properties, giving rise to conductance asymmetries and a selective suppression of the subband formation. Junction electrostatics and p-type characteristics drive the conduction mechanism in the case of high work function Au, Pd and Pt electrodes, while contact resistance becomes dominant in the case of Al., Comment: 4 pages, 5 figures

We present a systematic study of electron backscattering phenomena during conduction for graphene nanoribbons with single-vacancy scatterers and dimensions within the capabilities of modern lithographic techniques. Our analysis builds upon an \textit{ab initio} parameterized semiempirical model that breaks electron-hole symmetry and nonequilibrium Green's function methods for the calculation of the conductance distribution $g$. The underlying mechanism is based on wavefunction localizations and perturbations that in the case of the first $\pi-\pi{}^*$ plateau can give rise to impurity-like pseudogaps with both donor and acceptor characteristics. Confinement and geometry are crucial for the manifestation of such effects. Self-consistent quantum transport calculations characterize vacancies as local charging centers that can induce electrostatic inhomogeneities on the ribbon topology., Comment: 5 pages, 4 figures, accepted for publication at PRB