6,259 research outputs found

    Simulation of three dimensional current spreading in photonic crystal VCSEL structures

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    An efficient simulation technique for calculating the current distribution in a Vertical Cavity Surface Emitting Laser (VCSEL) is proposed and implemented. The technique consists of a hybrid 1D/3D approach to the problem. The 3D aspect of simulation is essential for devices like a photonic crystal VCSEL where the existing 2D simulation techniques are inadequate. The modular approach of the technique is advantageous, as it provides exibility in dealing with device simulations of varying complexity. It also provides a relatively short simulation time, beneficial for exploring a large design parameter space. The box integration technique is used for discretizing the equations and sparse matrix methods are used in solving the matrices. Simulation results and comparisons are provided for various aspects and modules of the simulator. The results for a few sample simulations indicate that the analysis has reasonable agreement with experimental results. The simulation error can be reduced using more accurate models for the active region of the laser.M.S.Committee Chair: Klein, Benjamin; Committee Member: Citrin, David; Committee Member: Ferguson, Ia

    A Variable-Structure Variable-Order Simulation Paradigm for Power Electronic Circuits

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    Solid-state power converters are used in a rapidly growing number of applications including variable-speed motor drives for hybrid electric vehicles and industrial applications, battery energy storage systems, and for interfacing renewable energy sources and controlling power flow in electric power systems. The desire for higher power densities and improved efficiencies necessitates the accurate prediction of switching transients and losses that, historically, have been categorized as conduction and switching losses. In the vast majority of analyses, the power semiconductors (diodes, transistors) are represented using simplified or empirical models. Conduction losses are calculated as the product of circuit-dependent currents and on-state voltage drops. Switching losses are estimated using approximate voltage-current waveforms with empirically derived turn-on and turn-off times

    Performance issues for iterative solvers in device simulation

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    Due to memory limitations, iterative methods have become the method of choice for large scale semiconductor device simulation. However, it is well known that these methods still suffer from reliability problems. The linear systems which appear in numerical simulation of semiconductor devices are notoriously ill-conditioned. In order to produce robust algorithms for practical problems, careful attention must be given to many implementation issues. This paper concentrates on strategies for developing robust preconditioners. In addition, effective data structures and convergence check issues are also discussed. These algorithms are compared with a standard direct sparse matrix solver on a variety of problems

    Numerical simulation of charge transport in disordered organic semiconductor devices

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    For the design of organic semiconductor devices such as organic light-emitting devices and solar cells, it is of crucial importance to solve the underlying charge transport equations efficiently and accurately. Only a fast and robust solver allows the use of fitting algorithms for parameter extraction and variation. Introducing appropriate models for organic semiconductors that account for the disordered nature of hopping transport leads to increasingly nonlinear and more strongly coupled equations. The solution procedures we present in this study offer a versatile, robust, and efficient means of simulating organic semiconductor devices. They allow for the direct solution of the steady-state drift-diffusion problem. We demonstrate that the numerical methods perform well in combination with advanced physical transport models such as energetic Gaussian disorder, density-dependent and field-dependent mobilities, the generalized Einstein diffusion, traps, and its consistent charge injection model.

    Unified simulation of transport and luminescence inoptoelectronic nanostructures

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    Computer simulation of microscopic transport and light emission in semiconductor nanostructures is often restricted to an isolated system of a single quantum well, wire or dot. In this work we report on the development of a simulator for devices with various kinds of nanostructures which exhibit quantization in different dimensionalities. Our approach is based upon the partition of the carrier densities within each quantization region into bound and unbound populations. A bound carrier is treated fully coherent in the directions of confinement, whereas it is assumed to be totally incoherent with a motion driven by classical drift and diffusion in the remaining directions. Coupling of the populations takes place through electrostatics and carrier capture. We illustrate the applicability of our approach with a well-wire structur

    Numerical methods for drift-diffusion models

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    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

    Mathematical modeling and numerical simulation of semiconductor detectors

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    We report on a system of nonlinear partial differential equations describing signal conversion and amplification in semiconductor detectors. We explain the main ideas governing the numerical treatment of this system as they are implemented in our code WIAS-TeSCA. This software package has been used by the MPI Semiconductor Laboratory for numerical simulation of innovative radiation detectors. We present some simulation results focussing on three-dimensional effects in X-ray detectors for satellite missions

    Numerical methods for drift-diffusion models

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    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 disretization scheme and recent efforts to generalize this approach to general statistical distribution functions

    Theory and simulation of quantum photovoltaic devices based on the non-equilibrium Green's function formalism

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    This article reviews the application of the non-equilibrium Green's function formalism to the simulation of novel photovoltaic devices utilizing quantum confinement effects in low dimensional absorber structures. It covers well-known aspects of the fundamental NEGF theory for a system of interacting electrons, photons and phonons with relevance for the simulation of optoelectronic devices and introduces at the same time new approaches to the theoretical description of the elementary processes of photovoltaic device operation, such as photogeneration via coherent excitonic absorption, phonon-mediated indirect optical transitions or non-radiative recombination via defect states. While the description of the theoretical framework is kept as general as possible, two specific prototypical quantum photovoltaic devices, a single quantum well photodiode and a silicon-oxide based superlattice absorber, are used to illustrated the kind of unique insight that numerical simulations based on the theory are able to provide.Comment: 20 pages, 10 figures; invited review pape
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