488 research outputs found
Semiclassical and relaxation limits of bipolar quantum hydrodynamic model
The global in-time semiclassical and relaxation limits of the bipolar quantum
hydrodynamic model for semiconductors are investigated in . We prove that
the unique strong solution converges globally in time to the strong solution of
classical bipolar hydrodynamical equation in the process of semiclassical limit
and to that of the classical Drift-Diffusion system under the combined
relaxation and semiclassical limits.Comment: 21 page
Algebraic time-decay for the bipolar quantum hydrodynamic model
The initial value problem is considered in the present paper for bipolar
quantum hydrodynamic model for semiconductors (QHD) in . We prove
that the unique strong solution exists globally in time and tends to the
asymptotical state with an algebraic rate as . And, we show that
the global solution of linearized bipolar QHD system decays in time at an
algebraic decay rate from both above and below. This means in general, we can
not get exponential time-decay rate for bipolar QHD system, which is different
from the case of unipolar QHD model (where global solutions tend to the
equilibrium state at an exponential time-decay rate) and is mainly caused by
the nonlinear coupling and cancelation between two carriers. Moreover, it is
also shown that the nonlinear dispersion does not affect the long time
asymptotic behavior, which by product gives rise to the algebraic time-decay
rate of the solution of the bipolar hydrodynamical model in the semiclassical
limit.Comment: 23 page
Global Existence and Large Time Behavior of Solutions to the Bipolar Nonisentropic Euler-Poisson Equations
We study the one-dimensional bipolar nonisentropic Euler-Poisson equations which can model various physical phenomena, such as the propagation of electron and hole in submicron semiconductor devices, the propagation of positive ion and negative ion in plasmas, and the biological transport of ions for channel proteins. We show the existence and large time behavior of global smooth solutions for the initial value problem, when the difference of two particles’ initial mass is nonzero, and the far field of two particles’ initial temperatures is not the ambient device temperature. This result improves that of Y.-P. Li, for the case that the difference of two particles’ initial mass is zero, and the far field of the initial temperature is the ambient device temperature
Nonlinear Coupled Effects in Nanomaterials
Materials at the nanoscale have different chemical, structural, and optoelectrical properties compared to their bulk counterparts. As a result, such materials, called nanomaterials, exhibit observable differences in certain physical phenomena. One such resulting phenomenon called the piezoelectric effect has played a crucial role in miniature self-powering electronic devices called nanogenerators which are fabricated by using nanostructures, such as nanowires, nanorods, and nanofilms. These devices are capable of harvesting electrical energy by inducing mechanical strain on the individual nanostructures. Electrical energy created in this manner does not have environmental limitations. In this thesis, important coupled effects, such as the nonlinear piezoelectric effect of a semiconducting wurtzite ZnO nanowire are studied by solving a time-dependent thermo-electromechanical model. For the examples considered here, the mathematical model consists of a system of fully-coupled nonlinear partial differential equations, and it is solved by using a variational formulation based on finite element representation. The numerical solution to this model is compared with the results obtained for the linear model of piezoelectric effect. The main focus has been given to the results from finite element analysis as a generalized model of the ZnO nanowire in order to understand its characteristics at an unperturbed state
Nonlinear Coupled Effects in Nanomaterials
Materials at the nanoscale have different chemical, structural, and optoelectrical properties compared to their bulk counterparts. As a result, such materials, called nanomaterials, exhibit observable differences in certain physical phenomena. One such resulting phenomenon called the piezoelectric effect has played a crucial role in miniature self-powering electronic devices called nanogenerators which are fabricated by using nanostructures, such as nanowires, nanorods, and nanofilms. These devices are capable of harvesting electrical energy by inducing mechanical strain on the individual nanostructures. Electrical energy created in this manner does not have environmental limitations. In this thesis, important coupled effects, such as the nonlinear piezoelectric effect of a semiconducting wurtzite ZnO nanowire are studied by solving a time-dependent thermo-electromechanical model. For the examples considered here, the mathematical model consists of a system of fully-coupled nonlinear partial differential equations, and it is solved by using a variational formulation based on finite element representation. The numerical solution to this model is compared with the results obtained for the linear model of piezoelectric effect. The main focus has been given to the results from finite element analysis as a generalized model of the ZnO nanowire in order to understand its characteristics at an unperturbed state
Numerical methods for drift-diffusion models
The van Roosbroeck system describes the semi-classical transport of free electrons and holes in a self-consistent electric field using a drift-diffusion approximation. It became the standard model to describe the current flow in semiconductor devices at macroscopic scale. Typical devices modeled by these equations range from diodes, transistors, LEDs, solar cells and lasers to quantum nanostructures and organic semiconductors. The report provides an introduction into numerical methods for the van Roosbroeck system. The main focus lies on the Scharfetter-Gummel finite volume discretization scheme and recent efforts to generalize this approach to general statistical distribution functions
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