83 research outputs found
Numerical Design Study on the Optimal p-Emitter Thickness of 4H-SiC Bipolar Diodes
Abstract Numerical device simulations show that slight extensions of the p-emitter thickness in 4H-SiC high voltage blocking bipolar pin diodes lead to a significant lowering of the forward voltage drop under high injection conditions at room temperature. The advantage of higher recombination currents in the enlarged p-region resulting from an enhanced excess carrier density overbalances the higher series resistance of the highdoped p-region. Both effects have their origin in the incomplete ionization of the acceptor dopants in the p-emitter. Hence, they become less significant at higher temperatures. A temperature dependent optimal p-emitter thickness is identified
Macromodel-based simulation and measurement of the dynamic pull-in of viscously damped RF-MEMS switches
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Analysis of Piezoresistive Effects in Silicon Structures Using Multidimensional Process and Device Simulation
Abstract With the view to analyzing piezoresistive effects in silicon microstructures we implemented a rigorous physically-based model in the multidimensional general purpose device simulator DESSIS'~~. In this model, the dependence of the piezoresistive coefficients on temperahue and doping concentration is included in a numerically hactable way. Using a commercial TCAD system (ISE), the practicability of the approach is demonstrated by performing a complete simulation sequence for realistic microdevices ranging from the layout design up to the analysis of the device operation
SiC power MOSFETs performance, robustness and technology maturity
Relatively recently, SiC power MOSFETs have transitioned from being a research exercise to becoming an industrial reality. The potential benefits that can be drawn from this technology in the electrical energy conversion domain have been amply discussed and partly demonstrated. Before their widespread use in the field, the transistors need to be thoroughly investigated and later validated for robustness and longer term stability and reliability. This paper proposes a review of commercial SiC power MOSFETs state-of-the-art characteristics and discusses trends and needs for further technology improvements, as well as device design and engineering advancements to meet the increasing demands of power electronics
Theoretical analysis of the electronic structure of the stable and metastable c(2x2) phases of Na on Al(001): Comparison with angle-resolved ultra-violet photoemission spectra
Using Kohn-Sham wave functions and their energy levels obtained by
density-functional-theory total-energy calculations, the electronic structure
of the two c(2x2) phases of Na on Al(001) are analysed; namely, the metastable
hollow-site structure formed when adsorption takes place at low temperature,
and the stable substitutional structure appearing when the substrate is heated
thereafter above ca. 180K or when adsorption takes place at room temperature
from the beginning. The experimentally obtained two-dimensional band structures
of the surface states or resonances are well reproduced by the calculations.
With the help of charge density maps it is found that in both phases, two
pronounced bands appear as the result of a characteristic coupling between the
valence-state band of a free c(2x2)-Na monolayer and the
surface-state/resonance band of the Al surfaces; that is, the clean (001)
surface for the metastable phase and the unstable, reconstructed "vacancy"
structure for the stable phase. The higher-lying band, being Na-derived,
remains metallic for the unstable phase, whereas it lies completely above the
Fermi level for the stable phase, leading to the formation of a
surface-state/resonance band-structure resembling the bulk band-structure of an
ionic crystal.Comment: 11 pages, 11 postscript figures, published in Phys. Rev. B 57, 15251
(1998). Other related publications can be found at
http://www.rz-berlin.mpg.de/th/paper.htm
Unoccupied Band Structure of NbSe2 by Very-Low-Energy Electron Diffraction: Experiment and Theory
A combined experimental and theoretical study of very-low-energy electron
diffraction at the (0001) surface of 2H-NbSe2 is presented. Electron
transmission spectra have been measured for energies up to 50 eV above the
Fermi level with k|| varying along the GammaK line of the Brillouin zone. Ab
initio calculations of the spectra have been performed with the extended linear
augmented plane wave k-p method. The experimental spectra are interpreted in
terms of three-dimensional one-electron band structure. Special attention is
paid to the quasi-particle lifetimes: by comparing the broadening of the
spectral structures in the experimental and calculated spectra the energy
dependence of the optical potential Vi is determined. A sharp increase of Vi at
20 eV is detected, which is associated with a plasmon peak in the
Im(-1/epsilon) function. Furthermore, the electron energy loss spectrum and the
reflectivity of NbSe2 are calculated ab initio and compared with optical
experiments. The obtained information on the dispersions and lifetimes of the
unoccupied states is important for photoemission studies of the 3D band
structure of the valence band.Comment: 17 pages, 11 Postscript figures, submitted to Phys. Rev.
Theory of traveling filaments in bistable semiconductor structures
We present a generic nonlinear model for current filamentation in
semiconductor structures with S-shaped current-voltage characteristics. The
model accounts for Joule self-heating of a current density filament. It is
shown that the self-heating leads to a bifurcation from static to traveling
filament. Filaments start to travel when increase of the lattice temperature
has negative impact on the cathode-anode transport. Since the impact ionization
rate decreases with temperature, this occurs for a wide class of semiconductor
systems whose bistability is due to the avalanche impact ionization. We develop
an analytical theory of traveling filaments which reveals the mechanism of
filament motion, find the condition for bifurcation to traveling filament, and
determine the filament velocity.Comment: 13 pages, 5 figure
Self-consistent Green’s-function technique for bulk and surface impurity calculations: Surface core-level shifts by complete screening
Combination of Thermal Subsystems Modelled by Rapid Circuit Transformation
This paper will deal with the modeling-problem of combining thermal subsystems (e.g. a semiconductor module or package with a cooling radiator) making use of reduced models. The subsystem models consist of a set of Foster-type thermal equivalent circuits, which are only behavioral models. A fast al-gorithm is presented for transforming the Foster-type circuits in Cauer-circuits which have physical behavior and therefore allow for the construction of the thermal model of the complete system. Then the set of Cauer-circuits for the complete system is transformed back into Foster-circuits to give a simple mathematical representation and applicability. The transfor-mation algorithms are derived in concise form by use of recur-sive relations. The method is exemplified by modeling and measurements on a single chip IGBT package mounted on a closed water cooled radiator. The thermal impedance of the complete system is constructed from the impedances of the sub-systems, IGBT-package and radiator, and also the impedance of the package can be inferred from the measured impedance of the complete system
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