1,477 research outputs found
Drift-diffusion models for the simulation of a graphene field effect transistor
AbstractA field effect transistor having the active area made of monolayer graphene is simulated by a drift-diffusion model coupled with the Poisson equation. The adopted geometry, already proposed in (Nastasi and Romano in IEEE Trans. Electron. Devices 68:4729–4734, 2021, 10.1109/TED.2021.3096492), gives a good current-ON/current-OFF ratio as it is evident in the simulations. In this paper, we compare the numerical simulations of the standard (non-degenerate) drift-diffusion model, that includes the Einstein diffusion coefficient, with the degenerate case
A Finite-Volume Scheme for a Spinorial Matrix Drift-Diffusion Model for Semiconductors
An implicit Euler finite-volume scheme for a spinorial matrix drift-diffusion
model for semiconductors is analyzed. The model consists of strongly coupled
parabolic equations for the electron density matrix or, alternatively, of
weakly coupled equations for the charge and spin-vector densities, coupled to
the Poisson equation for the elec-tric potential. The equations are solved in a
bounded domain with mixed Dirichlet-Neumann boundary conditions. The charge and
spin-vector fluxes are approximated by a Scharfetter-Gummel discretization. The
main features of the numerical scheme are the preservation of positivity and L
bounds and the dissipation of the discrete free energy. The existence
of a bounded discrete solution and the monotonicity of the discrete free energy
are proved. For undoped semiconductor materials, the numerical scheme is
uncon-ditionally stable. The fundamental ideas are reformulations using spin-up
and spin-down densities and certain projections of the spin-vector density,
free energy estimates, and a discrete Moser iteration. Furthermore, numerical
simulations of a simple ferromagnetic-layer field-effect transistor in two
space dimensions are presented
Generalized Scharfetter-Gummel schemes for electro-thermal transport in degenerate semiconductors using the Kelvin formula for the Seebeck coefficient
Many challenges faced in today's semiconductor devices are related to
self-heating phenomena. The optimization of device designs can be assisted by
numerical simulations using the non-isothermal drift-diffusion system, where
the magnitude of the thermoelectric cross effects is controlled by the Seebeck
coefficient. We show that the model equations take a remarkably simple form
when assuming the so-called Kelvin formula for the Seebeck coefficient. The
corresponding heat generation rate involves exactly the three classically known
self-heating effects, namely Joule, recombination and Thomson-Peltier heating,
without any further (transient) contributions. Moreover, the thermal driving
force in the electrical current density expressions can be entirely absorbed in
the diffusion coefficient via a generalized Einstein relation. The efficient
numerical simulation relies on an accurate and robust discretization technique
for the fluxes (finite volume Scharfetter-Gummel method), which allows to cope
with the typically stiff solutions of the semiconductor device equations. We
derive two non-isothermal generalizations of the Scharfetter-Gummel scheme for
degenerate semiconductors (Fermi-Dirac statistics) obeying the Kelvin formula.
The approaches differ in the treatment of degeneration effects: The first is
based on an approximation of the discrete generalized Einstein relation
implying a specifically modified thermal voltage, whereas the second scheme
follows the conventionally used approach employing a modified electric field.
We present a detailed analysis and comparison of both schemes, indicating a
superior performance of the modified thermal voltage scheme.Comment: 26 pages, 7 figure
Low-field electron mobility evaluation in silicon nanowire transistors using an extended hydrodynamic model
Silicon nanowires (SiNWs) are quasi-one-dimensional structures in which electrons are spatially confined in two directions and they are free to move in the orthogonal direction. The subband decomposition and the electrostatic force field are obtained by solving the Schrödinger–Poisson coupled system. The electron transport along the free direction can be tackled using a hydrodynamic model, formulated by taking the
moments of the multisubband Boltzmann equation. We shall introduce an extended hydrodynamic model where closure relations for the fluxes and production terms have been obtained by means of the Maximum Entropy Principle of Extended Thermodynamics, and in which the main scattering mechanisms such as those with phonons and surface roughness have been considered. By using this model, the low-field mobility of a Gate-All-Around SiNW transistor has been evaluated
Entropy Principle and Recent Results in Non-Equilibrium Theories
We present the state of the art on the modern mathematical methods of exploiting the entropy principle in thermomechanics of continuous media. A survey of recent results and conceptual discussions of this topic in some well-known non-equilibrium theories (Classical irreversible thermodynamics CIT, Rational thermodynamics RT, Thermodynamics of irreversible processes TIP, Extended irreversible hermodynamics EIT, Rational Extended thermodynamics RET) is also summarized
Preparation and caracterization of thermoelectric materials
This work presents a complete study of thermoelectric materials. It starts with a study
of a Solar Concentrator and the development of a Genetic Algorithm and Cross-Entropy
for analyzing experimental data. Contains a study on thermoelectric devices, from a new
experimental setup. It also counts on the development and manufacture of an entire
equipment for measuring thermoelectric materials, both bulks and thin films. It ends
with the preparation of a specific thermoelectric material, the MoS2, and the use of all
the apparatus previously developed for its study
Heat equations beyond Fourier: from heat waves to thermal metamaterials
In the past decades, numerous heat conduction models beyond Fourier have been
developed to account for the large gradients, fast phenomena, wave propagation,
or heterogeneous material structure, such as being typical for biological
systems, superlattices, or thermal metamaterials. It became a challenge to
orient among the models, mainly due to their various thermodynamic backgrounds
and possible compatibility issues. Additionally, in light of the recent
findings on the field of non-Fourier heat conduction, it is not even
straightforward how to interpret and utilize a non-Fourier heat equation,
primarily when one aims to thermally design the material structure to construct
the new generation of thermal metamaterials. Adding that numerous modeling
strategies can be found in the literature accompanying different
interpretations even for the same heat equation makes it even more difficult to
orient ourselves and find a comprehensive picture of this field of research.
Therefore, this review aims to ease the orientation among advanced heat
equations beyond Fourier by discussing properties concerning their possible
practical applications in light of experiments. We start from the simplest
model with basic principles and notions, then proceed toward the more complex
models related to coupled phenomena such as ballistic heat conduction. We do
not enter the often complicated technical details of each thermodynamic
framework but do not aim to compare each approach. However, we still briefly
present their background to highlight their origin and the limitations acting
on the models. Additionally, the field of non-Fourier heat conduction has
become quite segmented, and that paper also aims to provide a common ground, a
comprehensive mutual understanding of the basics of each model, together with
what phenomenon they can be applied to
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