It is clear that continued scaling of semiconductor devices will bring us to a regime with
gate lengths less than 50nm within another decade. The questions that must be
addressed in simulation are difficult. Pushing to dimensional sizes such as this will probe
the transition from classical to quantum transport, and there is no present approach to
this regime that has proved effective. Contrary to the classical case in which electrons are
negligibly small, the finite extent of the momentum space available to the electron set
size limitations on the minimum wave packet–this is of the order of a few nanometers–and leads to the effective potential. The latter is an approach to find the
equivalent classical potential, by which the actual potential is modified by quantum
effects. The use of the effective potential for analyzing the effect of quantization on
semiconductor devices will be discussed. The manner in which this leads to new
formulations for quantum transport will be discussed.

D. K. Ferry

Simulation at the Start of the New Millenium:
Crossing the Quantum-Classical Threshold

Focused Ion Beam MOSFETs (FIBMOS) demonstrate large enhancements in core device
performance areas such as output resistance, hot electron reliability and voltage stability
upon channel length or drain voltage variation. In this work, we describe an optimization
technique for FIBMOS threshold voltage characterization using the 2D Silvaco ATLAS
simulator. Both ATLAS and 2D Monte Carlo particle-based simulations were used to
show that FIBMOS devices exhibit enhanced current drive capabilities when compared to
normal MOSFETs. It was also found that the device performance is very much dependent
upon the FIB implant profile. High and narrow doping of the FIB implant leads to high
drain current and low hot carrier reliability, whereas low and wide doping gives rise to
lower drain current and higher hot carrier reliability.

J. Kang

X. He

D. Vasileska

D. K. Schroder

Optimization of FIBMOS Through 2D Silvaco
ATLAS and 2D Monte Carlo Particle-based
Device Simulations

We present a discussion of the complexities encountered in particle simulation models
for noncubic symmetry semiconductors, focusing on the wurtzite and 4H polytypes
of GaN and SiC. We have identified three general issues, band structure, scattering
mechanisms, and band intersections, which in our opinion, constitute the most important
modifications to conventional Monte Carlo simulators for cubic symmetry
semiconductors. It is found that the band intersection points present the greatest
modeling challenge. We discuss the effect of band intersections on the transport
dynamics and our initial attempts at treating transport near these points. Comparison to
experimental data is also made.

K. F. Brennan

E. Bellotti

M. Farahmand

H.-E. Nilsson

P. P. Ruden

Y. Zhang

Monte Carlo Modeling of Wurtzite and 4H Phase
Semiconducting Materials

Diffusion of boron in compressively strained Si1 &#8211;xGex alloy layers grown by rapidpressure chemical vapor deposition has been studied as a function of the compositionfor 0.0006 &#8804; x &#8804; 0.15 and annealing temperature. The comparison of the Si1 &#8211;xGexsamples to the Si samples after rapid thermal and furnace annealing revealed a retardedB diffusion inside the strained Si1 &#8211;xGex layers. The influence of the Ge content on thedopant diffusion was also measured and simulated, demonstrating that the diffusion ofB was found to decrease with the Ge alloy content and annealing temperature. A simpleempirical expression for the B retardation is presented and incorporated into a diffusionmodel for dopants in heterostructures. Good agreement between the measured andsimulated diffusivity that includes the model for strain and chemical effects are obtained.By comparing with experimental values, our extracted (by using experiment andsimulation) B diffusivity predicted a lower value (retardation).

K.  Rajendran

W.  Schoenmaker

Measurement and Simulation of Boron Diffusivityin Strained Si1 &#8211;xGex Epitaxial Layers

A set of software tools for the determination of the band structure of zinc-blende,
wurtzite, 4H, and 6H semiconductors is presented. A state of the art implementation of
the nonlocal empirical pseudopotential method has been coupled with a robust simplex
algorithm for the optimization of the adjustable parameters of the model potentials.
This computational core has been integrated with an array of Matlab functions, providing
interactive functionalities for defining the initial guess of the atomic pseudopotentials,
checking the convergence of the optimization process, plotting the resulting
band structure, and computing detailed information about any local minimum.
The results obtained for wurtzite-phase III-nitrides (ALN, GaN, InN) are presented as a
relevant case study.

Enrico Ghillino

Carlo Garetto

Michele Goano

Giovanni Ghione

Enrico Bellotti

Kevin F. Brennan

Simplex Algorithm for Band Structure Calculation
of Noncubic Symmetry Semiconductors:
Application to III-nitride Binaries and Alloys

Self-consistent quantum modeling of GaN-based nanostructure are presented. The
tight-binding approach is used to calculate optical properties while optimized effective
mass approaches are used to obtain the output characteristics of GaN HEMT.

F. Sacconi

F. Della Sala

A. Di Carlo

Paolo Lugli

Microscopic Modeling of GaN-based Heterostructures

The second-order nonrandom ordinary differential equation (ODE) system derived asthe noise-source-aware model for expectations of solutions of It&#244;&#39;s stochasticdifferential equation (ISDE) system is discussed in connection with large-scaleintegrated circuits (ICs). The work explains the reason why the new model consistentlyallows for the noise-induced phenomena in the expectations, namely, stochasticresonance, stochastic linearization, stochastic self-oscillations and stochastic chaos. Thecase of stochastic resonance is considered as an example. In spite of the fact that theabove second-order model is more complex than the nonrandom first-order IC ODEsystem for the expectations commonly used in engineering, an efficient practicaltechnique for its implementation is proposed. The corresponding predicted computingtime is only in 2.5 times greater than in the case of the first-order model which does notinclude any noise-source influence upon the expectations of the modelled IC responses.

Magnus  Willander

Yevgeny  Mamontov

Jonathan  Vincent

The Deterministic Circuit Model for Noise Influenceon the Averaged Transient Responses of Large-scaleNonlinear ICs Analyzed with It&#244;&#39;s StochasticDifferential Equations

Silica polymorphs have been analyzed, that are similar to the amorphous phase of SiO2;specifically, the &#945;- and &#946;-quartz, and the &#945;- and &#946;-cristobalite have been addressed. Twodifferent ab initio methods have been used to calculate the full-band structure and theelectronic properties of the polymorphs. In particular, the Hartree-Fock (HF) andDensity-Functional Theory (DFT) approaches have been selected. A comparison ofthe energy-band branches and DOS shapes is reported, showing the similarities ofthe electrical properties that characterize the polymorphs under study. Finally, somerelevant properties are compared for the analyzed set of polymorphs.

Elena  Gnani

Susanna  Reggiani

Renato  Colle

Massimo  Rudan

Calculation of Transport Parametersof SiO2 Polymorphs

It has been known for many years that interface roughness scattering, particularly off
the Si/SiO2 interface, is a limiting factor in device performance of MOSFETs. This
becomes increasingly important as gate lengths are shrunk to decanano dimensions
along with the move towards SiGe hetero-technology. However, analysis of interface
transport is hampered by the lack of detailed physical models, especially for surfaces
where intercalation occurs. This paper presents an efficient method for following the
motion of wave-packets scattering off a rough interface. We are also able to calculated
directly ab-initio interface scattering rates for use in Monte Carlo simulations.

J. R. Barker

J. R. Watling

R. C. W. Wilkins

A Fast Algorithm for the Study of Wave-packet
Scattering at Disordered Interfaces

Within the Wigner-function formalism for electron quantum transport in semiconductors
a two-time Wigner function is defined starting from the Green-function formalism.
After a proper Fourier transform a Wigner function depending on p and w as
independent variables is obtained. This new Wigner function extends the Wigner
formalism to the frequency domain and carries information related to the spectral
density of the system. A Monte Carlo approach based on the generation of Wigner
paths, already developed for the single-time Wigner function, has been extended to
evaluate the momentum and energy-dependent Wigner function. Results will be shown
for electrons subject to the action of an external field and in presence of scattering with
optical phonons.

R. Brunetti

A. Bertoni

P. Bordone

C. Jacoboni

Dynamical Equation and Monte Carlo Simulation
of the Two-time Wigner Function for Electron
Quantum Transport

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Published Special Issues

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Computional Electronics; Papers Presented at The Seventh International Workshop on Computional Electronics

Computional Electronics; Papers Presented at The Seventh International Workshop on Computional Electronics

Articles

Simulation at the Start of the New Millenium: Crossing the Quantum-Classical Threshold

Optimization of FIBMOS Through 2D Silvaco ATLAS and 2D Monte Carlo Particle-based Device Simulations

Monte Carlo Modeling of Wurtzite and 4H Phase Semiconducting Materials

Measurement and Simulation of Boron Diffusivity in Strained Si₁ –_xGe_x Epitaxial Layers

Simplex Algorithm for Band Structure Calculation of Noncubic Symmetry Semiconductors: Application to III-nitride Binaries and Alloys

Microscopic Modeling of GaN-based Heterostructures

The Deterministic Circuit Model for Noise Influence on the Averaged Transient Responses of Large-scale Nonlinear ICs Analyzed with Itô's Stochastic Differential Equations

Calculation of Transport Parameters of SiO₂ Polymorphs

A Fast Algorithm for the Study of Wave-packet Scattering at Disordered Interfaces

Dynamical Equation and Monte Carlo Simulation of the Two-time Wigner Function for Electron Quantum Transport