Molecular wires have several promising features, that would appear to make them ideal
for advanced interconnects in nanoscale electronic devices. We discuss several aspects of
the linear and nonlinear conductance of molecular wire interconnects. Topics include
energy dependence of molecular conductance, resonant tunneling behavior, control of
conductance by molecular structure and geometry, length dependence including the
tunneling regime energetics. Design rules using molecular interconnects will differ
substantially from those with more standard, lithographically structured silicon
interconnects. In particular, the dissipation mechanisms will differ, both tunneling and
ballistic regimes should be available, coulomb blockade and staircase behavior will be
observed (but under differing conditions) and fabrication of gate electrodes is a challenge.

Mathieu Kemp

Vladimiro Mujica

Adrian Roitberg

Mark A. Ratner

Molecular Wire Interconnects: Chemical Structural Control, Resonant Tunneling and
Length Dependence

We perform a rigorous comparison between the Spherical Harmonic (SH) and MonteCarlo (MC) methods of solving the Boltzmann Transport Equation (BTE), on a 0.05 &#956;mbase BJT. We find the SH and the MC methods give very similar results for the energydistribution function, using an analytical band-structure, at all points within the testeddevices. However, the SH method can be as much as seven thousand times faster than theMC approach for solving an identical problem. We explain the agreement by asymptoticanalysis of the system of equations generated by the SH expansion of the BTE.

C.-H.  Chang

C.-K.  Lin

N.  Goldsman

I. D. Mayergoyz

Spherical Harmonic Modeling of a 0.05 &#956;mBase BJT: A Comparison with Monte Carloand Asymptotic Analysis

We present three-dimensional numerical modeling results for gated Si/SiO2 quantum
dot systems in the few-electron regime. In our simulations, the electrostatic confining
potential results from the Poisson equation assuming a self-consistent Thomas-Fermi
charge model. We find that a very thin SiO2 top insulating layer allows an effective
control with single-electron confinement in quantum dots with radius less than 10nm
and investigate the detailed potential and resulting charge densities. Our three-dimensional
finite-element modeling tool allows future investigations of the charge
coupling in gated few-electron quantum-dot cellular automata.

Per Hyldgaard

Henry K. Harbury

Wolfgang Porod

Electrostatic Formation of Coupled Si/SiO2
Quantum Dot Systems

The microwave performance potential of Si/SiGe pseudomorphic MODFETs arestudied, in comparison to state of the art InGaAs pseudomorphic HEMTs. Both deviceshave equivalent structures corresponding to a physical HEMT used for calibration. Weuse an RF analysis technique based on transient Monte Carlo simulations to estimatethe intrinsic noise figures, the RF figures of merit fT and fmax, and the effect of contact and gate resistances. Both devices exhibit velocity overshoot below the gate region. It is shown that the difference in noise figures and fT values can be mainly attributed todifferences in device channel velocity, fmax exhibits a strong dependence on devicecontact resistance, eroding some of the performance advantage of the pseudomorphicHEMT.

S.  Roy

A.  Asenov

S.  Babiker

J. R. Barker

S. P. Beaumont

RF Performance of Si/SiGe MODFETs:A Simulation Study

We derive, using the Entropy Maximum Principle, an expression for the distributionfunction of carriers as a function of a set of macroscopic quantities (density, velocity,energy, deviatoric stress, energy flux). Given the distribution function, we obtain, forthese macroscopic quantities, a hydrodynamic model in which all the constitutivefunctions (fluxes and collisional productions) are explicitely computed starting fromtheir kinetic expressions. We have applied our model to the simulation of some onedimensionalsubmicron devices in a temperature range of 77&#8211;300 K, obtaining resultscomparable with Monte Carlo. Computation times are of order of few seconds for apicosecond of simulation.

P.  Falsaperla

M.  Trovato

A Hydrodynamic Model for Transportin Semiconductors without Free Parameters

We have been using a self-consistent formulation of full-wave electromagnetic solvers andensemble Monte Carlo techniques to model ultrafast photoconductivity. Our simulationsare running on a MasPar machine. This paper will address aspects ofthis simulation whichmay interest workers who are simulating not only photoconductive systems but othersystems as well which involve electrodynamics, waves and wave phenomena and ensembleMonte Carlo transport models. In particular, we will report on the inclusion of perfectlymatched layer approaches to absorbing boundary conditions for electromagnetic waves.These have in the past several years become widely used in computational electromagneticscodes because they reduce error due to spurious numerical wave reflection off ofan absorbing boundary by several orders of magnitude. We will also address the issue ofcomputational cost and show that a full-wave electromagnetic approach is morecompetitive with a Poisson&#39;s equation approach than one might believe. Lastly, oursystem has the feature that the active portion where the electrons and holes lie is in fact asmall fraction of the total experimental system&#39;s volume. Unless care is exerted one eitherhas a very significant load imbalance problem or high communications overhead. Wecompare two different tradeoffs between load imbalance and communications overhead.

Ik-Sung  Lim

Robert O. Grondin

Samir  El-Ghazaly

Ensemble Monte Carlo and Full-Wave ElectrodynamicModels Implemented Self-Consistently on a ParallelProcessor Using Perfectly Matched LayerBoundary Conditions

FDTD and Monte Carlo methods are combined to simulate the terahertz radiation
from a coplanar photoconducting structure. The simulation tool under consideration
allows calculation of potentials, particle distributions, current densities, and the near
field electromagnetic fields anywhere in the computational domain. To model the far
field radiation, it is not efficient nor, in many cases, physically possible at present to use
the FDTD technique directly because of the excessive computational burden.
Techniques are discussed for modeling both the near field and the far field radiation.
Computational results showing the far field radiation are in qualitative agreement with
published experimental results.

K. A. Remley

A. Weisshaar

V. K. Tripathi

S. M. Goodnick

Modeling of Radiation Fields in a Sub-Picosecond
Photo-Conducting System

Quantum transport is becoming more significant as device size shrinks. For example, asdevice sizes are scaled below 0.1 &#956;m, the number of impurities becomes quite small, sothat they are no longer homogeneously distributed throughout the device volume andthe carriers are localized into quantum boxes, in that self-energy corrections produced bylocally high carrier densities will lead to quantum dot formation. This leads to the needto discuss transport through an array of such quantum structures. Here, we discussseveral issues which must be considered in treating the transport through such devices.

D. K. Ferry

Open Problems in Quantum Simulationin Ultra-Submicron Devices

We perform self-consistent electronic structure calculations in the framework ofinhomogeneously and anisotropically scaled local density functional theory of a fully3D modeled Si/SiO2 quantum dot. Electrons are laterally confined in the semiconductor/oxide heterojunction by a metallic gate atop of the device. Total charge densities,total free energies, chemical potentials for different numbers of electrons in the dot, andthe differential capacitances for various dot sizes are calculated. We observe shell fillingeffects in the differential capacitance. The magic-numbers are governed by the six valleybandstructure of silicon, which leads to four fold degenerated single particle levels in thedot.

A.  Scholze

A.  Wettstein

A.  Schenk

W.  Fichtner

Self-Consistent Calculations of the Ground Stateand the Capacitance of a 3D Si/SiO2 Quantum Dot

A new numerical method is applied to the analysis of the charge partitioning in thequasi-neutral base of a BJT. The results show that the conventional, 1:2 collector/emitter partitioning is not valid in general. High level injection increases the collectorfraction, whilst fast switching decreases it.

Michael S. Obrecht

Edwin L. Heasell

J.  Vlach

Mohamed I. Elmasry

Transient Phenomena in High Speed Bipolar Devices

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