We investigate the dependence of the capacitive energy associated with a circular
quantum dot on the number of electrons in the dot and on the parameters defining the
potential confinement. Our results reproduce the shell-filling behavior that has recently
been experimentally observed and allow us to estimate the shape of the confinement
potential and the dot size of the experiments.

M. Macucci

Karl Hess

Shell-Filling Effects in Circular Quantum Dots

Relaxation time due to electron-longitudinal-acoustic (LA) phonon interaction iscalculated in a GaAs quantum dot (QD) with N electrons (from N &#61; 1 to 4), whereelectrons in a narrow quantum well are confined by a parabolic confining potential, byusing the exact eigen states of electrons. Although the energy levels become dense withincreasing the number of electrons, the modification of the relaxation time is found to benot so strong, which attributes the fact that many electron eigen states consist of only afew dominant single electron states which limit the electron relaxation. By comparingrelaxation process via intermediate states with the direct process, several fastestprocesses are found to be realized by relaxation through intermediate states between theinitial state and the ground state. The effect of change in the quantum well width is alsodiscussed.

T.  Ezaki

N.  Mori

C.  Hamaguchi

Electron-LA Phonon Interaction in a Quantum Dot

We develop a quantitative model of the impact-ionizationand hot-electron&#8211;injectionprocesses in MOS devices from first principles. We begin by modeling hot-electrontransport in the drain-to-channel depletion region using the spatially varying Boltzmanntransport equation, and we analytically find a self consistent distribution function in atwo step process. From the electron distribution function, we calculate the probabilitiesof impact ionization and hot-electron injection as functions of channel current, drainvoltage, and floating-gate voltage. We compare our analytical model results tomeasurements in long-channel devices. The model simultaneously fits both the hot-electron-injection and impact-ionization data. These analytical results yield an energydependentimpact-ionization collision rate that is consistent with numerically calculatedcollision rates reported in the literature.

Paul  Hasler

Andreas G. Andreou

Chris  Diorio

Bradley A. Minch

Carver A. Mead

Impact Ionization and Hot-Electron Injection DerivedConsistently from Boltzmann Transport

In this paper we present a methodology to use drift diffusion (DD) simulations in the
design of short channel heterojunction FETs (HFETs) with well pronounced velocity
overshoot. In the DD simulations the velocity overshoot in the channel is emulated by
forcing the saturation velocity in the field dependent mobility model to values
corresponding to the average velocity in the channel obtained from Monte Carlo (MC)
simulation. To illustrate our approach we compare enhanced DD and MC simulation
results for a pseudomorphic HEMTs with 0.12 μm channel length, which are in good
agreement. The usefulness of the described methodology is illustrated in a simulation
example of self aligned gamma gate pseudomorphic HEMTs. The effect of the gamma
gate shape and the self aligned contacts on the overall device performance has been
investigated.

A. Asenov

S. Babiker

S. P. Beaumont

J. R. Barker

Monte Carlo Calibrated Drift-Diffusion Simulation
of Short Channel HFETs

We present systematic theoretical Cellular Automata (CA) studies of a novel nanometer
scale Si device, namely vertically grown Metal Oxide Field Effect Transistors
(MOSFET) with channel lengths between 65 and 120 nm. The CA simulations predict
drain characteristics and output conductance as a function of gate length. The excellent
agreement with available experimental data indicates a high quality oxide/semiconductor
interface. Impact ionization is shown to be of minor importance. For
inhomogeneous p-doping profiles along the channel, significantly improved drain
current saturation is predicted.

M. Saraniti

G. Zandler

G. Formicone

S. Goodnick

Cellular Automata Studies of Vertical Silicon Devices

By using an energy transport model, we simulate cutoff frequency <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>f</mml:mi><mml:mi>T</mml:mi></mml:msub><mml:mtext>&#x2009;</mml:mtext></mml:math> versus collectorcurrent density <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>I</mml:mi><mml:mi>C</mml:mi></mml:msub></mml:math> characteristics of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>n</mml:mi><mml:mi>p</mml:mi><mml:msup><mml:mi>n</mml:mi><mml:mo>&#x2212;</mml:mo></mml:msup><mml:mi>n</mml:mi></mml:math> AlGaAs/GaAs heterojunction bipolartransistors (HBTs) with various <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi>n</mml:mi><mml:mo>&#x2212;</mml:mo></mml:msup></mml:math>-collector thickness and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi>n</mml:mi><mml:mo>&#x2212;</mml:mo></mml:msup></mml:math>-doping densities. It isfound that the calculated <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>f</mml:mi><mml:mi>T</mml:mi></mml:msub><mml:mtext>&#x2009;</mml:mtext></mml:math> characteristics show double peak behavior when the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi>n</mml:mi><mml:mo>&#x2212;</mml:mo></mml:msup></mml:math>-layer is thick enough and the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi>n</mml:mi><mml:mo>&#x2212;</mml:mo></mml:msup></mml:math>-doping is high enough to allow existence of neutral <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi>n</mml:mi><mml:mo>&#x2212;</mml:mo></mml:msup></mml:math>-region. The mechanism of the double peak behavior is discussed by studying energyband diagrams, electron-energy profiles and electron-velocity profiles. Particularly, wediscuss the origin of the second peak (at higher <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>I</mml:mi><mml:mi>C</mml:mi></mml:msub></mml:math>) which is not usually reportedexperimentally.

T.  Okada

K.  Horio

Study on Possible Double Peaks in CutoffFrequency Characteristics of AlGaAs/GaAsHBTs by Energy Transport Simulation

Good agreement between a hydrodynamic and a Monte-Carlo device model isdemonstrated in this paper for an advanced SiGe Heterojunction Bipolar Transistor.This result is based on two principles: 1) Extraction (from the Monte-Carlo bulk modelunder homogeneous conditions) of the relaxation times &#964; at discrete points of theparameter space spanned by the Ge-content x, doping density N, carrier temperature <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>T</mml:mi><mml:mi>C</mml:mi></mml:msub></mml:mrow></mml:math>and lattice temperature <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>T</mml:mi><mml:mi>L</mml:mi></mml:msub><mml:mo>.</mml:mo><mml:mtext>&#x2009;</mml:mtext><mml:mn>2</mml:mn></mml:mrow></mml:math>) Modeling of the relaxation times <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>&#x03C4;</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mi>x</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x2009;</mml:mtext><mml:mtext>&#x2009;</mml:mtext><mml:msub><mml:mi>T</mml:mi><mml:mi>C</mml:mi></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x2009;</mml:mtext><mml:mtext>&#x2009;</mml:mtext><mml:msub><mml:mi>T</mml:mi><mml:mi>L</mml:mi></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math> bysplines.

B.  Neinh&#252;s

S.  Decker

P.  Graf

F. M. Bufler

B.  Meinerzhagen

Consistent Hydrodynamic and Monte-Carlo Simulationof SiGe HBTs Based on Table Modelsthe Relaxation Times

Non-local electron transport in nMOSFET inversion layers has been studied by Monte
Carlo (MC) simulations. Inversion layer quantization has been explicitly included in the
calculation of density of states and scattering rate for low-energy electrons while bulk
band structure is used to describe the transport of more energetic electrons. For
uniform, high-lateral field conditions, the effects of quantization are less pronounced
due to the depopulation of electrons in the lower-lying subbands. On the other hand,
Monte Carlo results for carrier transport in spatially varying lateral fields (such as those
in the inversion layer of MOSFETs) clearly indicate that depopulation of the low-lying
subbands is less evident in the non-local transport regime. Quasi-2D simulations have
shown that, at high transverse effective field, the inclusion of a quantization domain
does have an impact on the calculated spatial velocity transient.

Wei-Kai Shih

Srinivas Jallepalli

Mahbub Rashed

Christine M. Maziar

Al. F. Tasch Jr.

Study of Electron Velocity Overshoot in NMOS
Inversion Layers

A self-consistent numerical simulation model for a pin single-cell solar cell is formulated.The solar cell device consists of a p&#8211;AlGaAs region, an intrinsic i&#8211;AlGaAs/GaAsregion with several quantum wells, and a n&#8211;AlGaAs region. Our simulator solves afield-dependent Schr&#246;dinger equation self-consistently with Poisson and drift-diffusionequations. The field-dependent Schr&#246;dinger equation is solved using the transfer matrixmethod. The eigenfunctions and eigenenergies obtained are used to calculate the escaperate of carriers from the quantum wells, the capture rates of carriers by the wells, theabsorption spectra in the wells, and the non-radiative recombination rates of carriers inthe quantum wells. These rates are then used in a self-consistent finite-differencenumerical Poisson-drift-diffusion solver. We believe this is the first such comprehensivemodel ever reported.

S.  Ramey

R.  Khoie

Formulation of a Self-Consistent Model for QuantumWell pin Solar Cells: Dark Behavior

A fully coupled electro-thermal hydrodynamic model is described which is suitable for
modelling active devices. The model is applied to the non-isothermal simulation of
pseudomorphic high electron mobility transistors (pHEMTs). A large-scale surface
temperature model is described which allows thermal modelling of semiconductor
devices and monolithic circuits. An example of the application of thermal modelling to
monolithic circuit characterization is given.

Christopher M. Snowden

Modeling of Thermal Effects in Semiconductor Structures

About this journal

Journal profile

Meet the editorial board

Editor spotlight

Submit your proposal

Do you think there is an emerging area of research that really needs to be highlighted? Or an existing research area that has been overlooked or would benefit from deeper investigation? Raise the profile of a research area by leading a Special Issue.

Special Issues

title

https://images.hindawi.com/journals/vlsi/vlsi.banner.jpg

twitter:card

twitter:site

twitter:title

twitter:url

twitter:image

VLSI Design | Hindawi

VLSI Design

This Issue is now open for submissions.
Papers are published upon acceptance, regardless of the Special Issue publication date.

Call for papers

Wolfgang Porod