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Linear current-voltage pattern, has been and continues to be the basis for characterizing, evaluating performance, and designing integrated circuits, but is shown not to hold its supremacy as channel lengths are being scaled down. In a nanoscale circuit with reduced dimensionality in one or more of the three Cartesian directions, quantum effects transform the carrier statistics. In the high electric field, the collision free ballistic transform is predicted, while in low electric field the transport remains predominantly scattering-limited. In a micro/nano-circuit, even a low logic voltage of 1 V is above the critical voltage triggering nonohmic behavior that results in ballistic current saturation. A quantum emission may lower this ballistic velocity.
The semiconductor industry, in its continued effort to scale down nanoscale components further, needs to predict the physical properties of future components. As the size of such devices shrinks down, the currently prevalent semi-classical models start to fall apart, as quantum effects that are usually invisible in larger silicon devices gain in relevance in smaller and/or III-V based semiconductor devices. Therefore, modeling and simulation tools should describe adequately the favorite technological options that are currently under investigation. Consequently, full quantum simulations are necessary to the development of modern field effect transistors.The purpose of this PhD thesis is to develop the tools suitable for those simulations and use them to look into some of the most relevant design options for transistor technology.Hence, we used the Non Equilibrium Green's Functions formalism to simulate charge carriers transport and investigate field effect transistors.The semiconductor band structures were calculated within a continuous kp formalism, but we also developed an atomistic effective pseudopotential method to perform full-band simulations with a variety of ingredients like arbitrary crystal orientation, surface roughness, arbitrary alloy composition in the transistor channel, and so on. This pseudopotential method provides accurate results for a wider array of configurations with a smaller parametrization effort than the k.p formalism.We used these simulation tools to evaluate the transport properties of silicon and InAs based FinFETs, focusing on the supply-voltage scalability of III-V based devices compared to silicon counterparts. In particular, the feasibility of obtaining large on-current values in III-V devices is discussed.Then, we applied that formalism to III-V based gate all-around (GAA) nanowire tunnel-FETs (TFETs). Tunnel-FETs are a promising architecture for future transistors, facing optimization and performance challenges. We aimed at benchmarking the effect of technological boosters on the performances of TFETs, namely the use of strain engineering and of III-V heterojunctions. We've shown that these boosters allow TFETs to theoretically outperform standard MOSFET technology, but that strain engineering induces undesirable drawbacks.In order to design high performance TFETs without the use of strain, we finally introduced novel design options by exploiting a molar fraction grading of a ternary alloy or alternatively a quantum well in the source region. These device configurations dramatically change the density of state of the TFET at the source/channel junction and are therefore able to improve the electrical performance of TFETs with respect to conventional MOSFETs.
Rapid developments in technology have led to enhanced electronic systems and applications. When utilized correctly, these can have significant impacts on communication and computer systems. Transport of Information-Carriers in Semiconductors and Nanodevices is an innovative source of academic material on transport modelling in semiconductor material and nanoscale devices. Including a range of perspectives on relevant topics such as charge carriers, semiclassical transport theory, and organic semiconductors, this is an ideal publication for engineers, researchers, academics, professionals, and practitioners interested in emerging developments on transport equations that govern information carriers.
This book introduces readers to state-of-the-art theoretical and simulation techniques for determining transport in complex band structure materials and nanostructured-geometry materials, linking the techniques developed by the electronic transport community to the materials science community. Starting from the semi-classical Boltzmann Transport Equation method for complex band structure materials, then moving on to Monte Carlo and fully quantum mechanical models for nanostructured materials, the book addresses the theory and computational complexities of each method, as well as their advantages and capabilities. Presented in language that is accessible to junior computational scientists, while including enough detail and depth with regards to numerical implementation to tackle modern research problems, it offers a valuable resource for computational scientists and postgraduate researchers whose work involves the theory and simulation of electro-thermal transport in advanced materials.
Provides the theoretical background needed by physicists, engineers and students to simulate nano-devices, semiconductor quantum dots and molecular devices. It presents in a unified way the theoretical concepts, the more recent semi-empirical and ab initio methods, and their application to experiments. The topics include quantum confinement, dielectric and optical properties, non-radiative processes, defects and impurities, and quantum transport. This guidebook not only provides newcomers with an accessible overview (requiring only basic knowledge of quantum mechanics and solid-state physics) but also provides active researchers with practical simulation tools.
Modeling nanoscale devices quantum mechanically is a computationally challenging problem where new methods to solve the underlying equations are in a dire need. In this Ph.D. work, we design and implement an efficient and high quality numerical algorithm to solve Green's functions, within the framework of non-equilibrium Green's function (NEGF) calculation, which is the most accurate approach in electronic transport simulation. Our approach exploits and extends a recent advance in using an established graph partitioning method, namely the nested dissection. The developed method has the capability to handle open boundary conditions that are represented by full self-energy matrices required for realistic modeling of nanoscale devices. We demonstrate that our method has a reduced complexity and significant speedup compared to the state-of-the-art recursive Green's function (RGF) approach across a variety of two-dimensional systems and, more important, three-dimensional structures including the traditional silicon nanowire, emerging graphene based multilayer devices, and DNA molecules. As a novel application of the proposed simulator, we investigate the tunneling transport properties of heterostructures consisting of a few atomic layers thick hexagonal Boron Nitride (hBN) film sandwiched between armchair edged graphene nanoribbon electrodes. By incorporating our efficient Green's function solver, the modeled device ranges from a small system with 6,000 atoms to experimental feasible sizes up to 70,000 atoms. We show a gate-controllable vertical transistor exhibiting strong negative differential resistance (NDR) effect with multiple resonant peaks, which originate from two distinct mechanisms depending on the gate and applied bias in the same device. We perform a scaling analysis of the NDR feature as a function of the system size and gain instructive insights for future theoretical and experimental investigations. To convey more experimentally realistic simulation, we incorporate (i) angular misorientation between multilayer heterostructure, which inducing a distinct resonant mechanism depending on both gate bias and twisting angle; (ii) electron-phonon scattering decoherence mechanism, which successfully captures the current NDR peaks degradation observed in room-temperature experiments. The NDR feature with multiple resonant peaks, combined with the ultrafast tunneling speed provides prospect for the graphene-hBN-graphene heterostructure in the high-performance electronics.
Mesoscopic physics deals with systems larger than single atoms but small enough to retain their quantum properties. The possibility to create and manipulate conductors of the nanometer scale has given birth to a set of phenomena that have revolutionized physics: quantum Hall effects, persistent currents, weak localization, Coulomb blockade, etc. This Special Issue tackles the latest developments in the field. Contributors discuss time-dependent transport, quantum pumping, nanoscale heat engines and motors, molecular junctions, electron–electron correlations in confined systems, quantum thermo-electrics and current fluctuations. The works included herein represent an up-to-date account of exciting research with a broad impact in both fundamental and applied topics.
Swift ion beam analysis (IBA) of materials and their surfaces has been widely applied to many fields over the last half century, constantly evolving to meet new requirements and to take advantage of developments in particle detection and data treatment. Today, emerging fields in nanosciences introduce extreme demands to analysis methods at the nanoscale. This book addresses how analysis with swift ion beams is rising to meet such needs. Aimed at early stage researchers and established researchers wishing to understand how IBA can contribute to their analytical requirements in nanosciences, the basics of the interactions of charged particles with matter, as well as the operation of the relevant equipment, are first presented. Many recent examples from nanoscience research are then explored in which the specific analytical capabilities of IBA are emphasized, together with the place of IBA alongside the wealth of other analytical methods.
The advent of semiconductor structures whose characteristic dimensions are smaller than the mean free path of carriers has led to the development of novel devices, and advances in theoretical understanding of mesoscopic systems or nanostructures. This book has been thoroughly revised and provides a much-needed update on the very latest experimental research into mesoscopic devices and develops a detailed theoretical framework for understanding their behaviour. Beginning with the key observable phenomena in nanostructures, the authors describe quantum confined systems, transmission in nanostructures, quantum dots, and single electron phenomena. Separate chapters are devoted to interference in diffusive transport, temperature decay of fluctuations, and non-equilibrium transport and nanodevices. Throughout the book, the authors interweave experimental results with the appropriate theoretical formalism. The book will be of great interest to graduate students taking courses in mesoscopic physics or nanoelectronics, and researchers working on semiconductor nanostructures.
Ballistic transport simulation in nanodevices, which involves self-consistently solving a coupled Schrodinger-Poisson system of equations, is usually computationally intensive. Here, we propose coupling the reduced basis method with the subband decomposition method to improve the overall efficiency of the simulation. By exploiting a posteriori error estimation procedure and greedy sampling algorithm, we are able to design an algorithm where the computational cost is reduced significantly. In addition, the computational cost only grows marginally with the number of grid points in the confined direction.