The Los Alamos 3D grid toolbox handles grid maintenance chores and provides accessto a sophisticated set of optimization algorithms for unstructured grids. The applicationof these tools to semiconductor problems is illustrated in three examples: grain growth,topographic deposition and electrostatics. These examples demonstrate adaptivesmoothing, front tracking, and automatic, adaptive refinement/derefinement.

Andrew  Kuprat

David  Cartwright

J. Tinka Gammel

Denise  George

Brian  Kendrick

David  Kilcrease

Harold  Trease

Robert  Walker

X3D Moving Grid Methods for Semiconductor Applications

We present a fast and robust iterative method for obtaining self-consistent solutions to the
coupled system of Schrödinger's and Poisson's equations in quantum structures. A simple
expression describing the dependence of the quantum electron density on the electrostatic
potential is used to implement a predictor – corrector type iteration scheme for the solution
of the coupled system of differential equations. This approach simplifies the software
implementation of the nonlinear problem, and provides excellent convergence speed and
stability. We demonstrate the algorithm by presenting an example for the calculation ofthe
two-dimensional bound electron states within the cross-section of a GaAs-AlGaAs based
quantum wire. For this example, six times fewer iterations are needed when our predictor – corrector
approach is applied, compared to a corresponding underrelaxation algorithm.

A. Trellakis

A. T. Galick

A. Pacelli

U. Ravaioli

Comparison of Iteration Schemes for the Solution of the
Multidimensional Schrödinger-Poisson Equations

We generalize the Multiband Quantum Transmitting Boundary Method (MQTBM) for
computing transmission coefficients in heterostructure to tight-binding-like band
structure models with non-orthogonal basis and multiple neighbor interactions. We
implement this method based on the newly developed planar-basis pseudopotential
method which uses the generalized planar Wannier function basis. We demonstrate the
method by computing transmission coefficients for a GaAs/AlAs double barrier
structure.

G.-C. Liang

Y. A. Lin

D. Z.-Y. Ting

Y.-C. Chang

Multiband Quantum Transmitting Boundary Method
for Non-orthogonal Basis

An important class of biological molecules-proteins called ionic channels&#8211;conductions (like Na+, K+, Cl-) through a narrow tunnel of fixed charge (&#8216;doping&#8217;). Ionic channels are the main pathway by which substances move into cells and so are of greatbiological and medical importance: a substantial fraction of all drugs used by physicians act on channels. Channels can be studied in the tradition of computational electronics. Drift diffusion equations form an adequate model of IV relations of 6 different channel proteins in &#820; 10 solutions over &#177;150 mV. Ionic channels can also be studied with thepowerful techniques of molecular biology. Atoms can be modified one at a time and the location of every atom can be determined. Ionic channels are natural nanotubes that can be controlled more precisely and easily than physical nanostructures but biologists need help if realistic simulations are to be done atomic detail.

Bob  Eisenberg

Ionic Channels in Biological Membranes: NaturalNanotubes Described by the Drift-Diffusion Equations

In this paper we describe the use of 3D parallel finite element solution of the Poissonequation to calculate the in-cell breakdown voltage in lateral channel IGBTs. The solveris based on topologically rectangular grids, and uses a domain decomposition approachto partition the problem on an array of mesh connected processors. A parallelBiCGSTAB solver has been developed to solve the Possion equation. Hole and electronionisation integrals are calculated to determine the breakdown voltage. The effects ofvarying the doping concentration in the n&#8211; base region and stopper surfaceconcentration are investigated.

A. R. Brown

A.  Asenov

J. R. Barker

3D Parallel Finite Element Simulation of In-Cell Breakdown in Lateral-Channel IGBTs

As devices shrink to dimensions below 0.1 &#956;m, it becomes essential to treat impuritiesand carriers as individual charges. We describe some approaches to ionised impurityscattering where the potential of the impurities is included directly in the dynamics of aMonto Carlo type simulation rather than as a scattering rate. The divergence in theCoulomb potential creates difficulties for mesh-based solutions of Poisson&#39;s equation,which we have compared with more accurate Ewald summation. However, we find thatthe mesh does not introduce significant errors, and reproduces well the expectedmobility as a function of doping. Highly accurate integration of the equation of motionis needed for free carriers, and the initial distribution is problematic. In contrast, asimple treatment of phonon scattering by Brownian dynamics is more tolerant of errorsbecause it tends to restore the system to equilibrium.

C. R. Arokianathan

J. H. Davies

Ab-initio Coulomb Scattering in AtomisticDevice Simulation

The superposition principle makes quantum networks behave very differently from their
classical counterparts: We discuss how local and non-local coherence are generated and
how these may affect the function of composite systems. Numerical examples concern
quantum trajectories, quantum noise and quantum parallelism.

Günter Mahler

Rainer Wawer

Quantum Networks: Dynamics of Open Nanostructures

The problem of obtaining the lasing modes and corresponding threshold conditions for vertical cavity surface emitting lasers (VCSELs) is formulated as a frequency-dependent eigenvalue problem in required gain amplitudes and corresponding fields. Both index and gain guiding are treated on an equal footing. The complex gain eigenvalues define necessary but not sufficient conditions for lasing. The actual lasing frequencies and
modes that the VCSEL can support are then determined by matching the gain necessary for the optical system in both magnitude and phase to the gain available from the laser's electronic system. Examples are provided.

Benjamin Klein

Leonard F. Register

Karl Hess

Dennis Deppe

Theory and Modeling of Lasing Modes  in Vertical Cavity Surface Emitting Lasers

Quantum transport in multiple-barrier systems exposed to intense laser fields isinvestigated by employing an analogy with the Fabry-Perot interferometer of classicaloptics. This analogy is exact if no further approximations are introduced. The Fabry-Perot approach is shown to be quite robust: Approximating the barriers by &#948;-functionswith equivalent dc transmission and reflection amplitudes still yields excellent agreementwith &#8220;exact&#8221; orthodox transfer-matrix calculations. The advantage of the former is itsmuch reduced computational demands as well as ease of use. 73.40.Gk, 73.50.Pz,72.40. + w, 42.50.Hz.

Mathias  Wagner

A New Computational Approach to Photon-AssistedTunneling in Intense Driving Fields Basedon a Fabry-Perot Analogy

A hydrodynamical model for semiconductors based on Extended Thermodynamics ispresented and a suitable numerical scheme is proposed.

Angelo Marcello Anile

Vittorio  Romano

Giovanni  Russo

Hyperbolic Hydrodynamical Model of CarrierTransport in Semiconductors

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