Semiconductor Device Modeling and Simulation for Electronic Circuit Design

This chapter covers different methods of semiconductor device modeling for electronic circuit simulation. It presents a discussion on physics-based analytical modeling approach to predict device operation at specific conditions such as applied bias (e.g., voltages and currents); environment (e.g., temperature, noise); and physical characteristics (e.g., geometry, doping levels). However, formulation of device model involves trade-off between accuracy and computational speed and for most practical operation such as for SPICE-based circuit simulator, empirical modeling approach is often preferred. Thus, this chapter also covers empirical modeling approaches to predict device operation by implementing mathematically fitted equations. In addition, it includes numerical device modeling approaches, which involve numerical device simulation using different types of commercial computer-based tools. Numerical models are used as virtual environment for device optimization under different conditions and the results can be used to validate the simulation models for other operating conditions

Compact modelling in RF CMOS technology

With the continuous downscaling of complementary metal-oxide-semiconductor (CMOS) technology, the RF performance of metal-oxide-semiconductor field transistors (MOSFETs) has considerably improved over the past years. Today, the standard CMOS technology has become a popular choice for realizing radio frequency (RF) applications. The focus of the thesis is on device compact modelling methodologies in RF CMOS. Compact models oriented to integrated circuit (ICs) computer automatic design (CAD) are the key component of a process design kit (PDK) and the bridge between design houses and foundries. In this work, a novel substrate model is proposed for accurately characterizing the behaviour of RF-MOSFETs with deep n-wells (DNW). A simple test structure is presented to directly access the substrate parasitics from two-port measurements in DNWs. The most important passive device in RFIC design in CMOS is the spiral inductor. A 1-pi model with a novel substrate network is proposed to characterize the broadband loss mechanisms of spiral inductors. Based on the proposed 1-pi model, a physics-originated fully-scalable 2-pi model and model parameter extraction methodology are also presented for spiral inductors in this work. To test and verify the developed active and passive device models and model parameter extraction methods, a series of RF-MOSFETs and planar on-chip spiral inductors with different geometries manufactured by employing standard RF CMOS processes were considered. Excellent agreement between the measured and the simulated results validate the compact models and modelling technologies developed in this work

Compact Models for Integrated Circuit Design

This modern treatise on compact models for circuit computer-aided design (CAD) presents industry standard models for bipolar-junction transistors (BJTs), metal-oxide-semiconductor (MOS) field-effect-transistors (FETs), FinFETs, and tunnel field-effect transistors (TFETs), along with statistical MOS models. Featuring exercise problems at the end of each chapter and extensive references at the end of the book, the text supplies fundamental and practical knowledge necessary for efficient integrated circuit (IC) design using nanoscale devices. It ensures even those unfamiliar with semiconductor physics gain a solid grasp of compact modeling concepts

Modeling and Simulation in Engineering

The general aim of this book is to present selected chapters of the following types: chapters with more focus on modeling with some necessary simulation details and chapters with less focus on modeling but with more simulation details. This book contains eleven chapters divided into two sections: Modeling in Continuum Mechanics and Modeling in Electronics and Engineering. We hope our book entitled "Modeling and Simulation in Engineering - Selected Problems" will serve as a useful reference to students, scientists, and engineers

ANALYTICAL COMPACT MODELING OF NANOSCALE MULTIPLE-GATE MOSFETS.

L’objectiu principal d’aquest treball és el desenvolupament d’un model compacte per a MOSFETs de múltiple porta d’escala nanomètrica, que sigui analític, basat en la física del dispositiu, i predictiu per a simulacions AC i DC. Els dispositius investigats són el MOSFET estàndar en mode d’inversió, a més d’un nou dispositiu anomenat “junctionless MOSFET” (MOSFET sense unions). El model es va desenvolupar en una formulació compacta amb l’ajuda de l’equació de Poisson i la tècnica de la transformación conforme de Schwarz-Cristoffel. Es varen obtenir les equacions del voltatge llindar i el pendent subllindar. Usant la funció W de Lambert, a més d’una funció de suavització per a la transcició entre les regions de depleció i acumulació, s’obté un model unificat de la densitat de càrrega, vàlid per a tots els modes d’operació del transistor. S’estudien també les dependències entre els paràmetres físics del dispositiu i el seu impacte en el seu rendiment. Es tenen en compteefectes importants de canal curt i de quantització. Es discuteixen també la simetria al voltant de Vds= 0 V, i la continuïtat del corrent de drenador en les derivades d’ordre superior. El model va ser validat mitjançant simulacions TCAD numèriques i mesures experimentals.El objetivo principal de este trabajo es el desarrollo de un modelo compacto para MOSFETs de múltiple puerta de escala nanométrica, que sea analítico, basado en la física del dispositivo, y predictivo para simulaciones AC y DC. Los dispositivos investigados son el MOSFET estándar en modo inversión, además de un nuevo dispositivo llamado “junctionless MOSFET” (MOSFET sin uniones). El modelo se desarrolló en una formulación compacta con la ayuda de la ecuación de Poisson y la técnica de transformación conforme de Schwarz-Cristoffel. Se obtuvieron las ecuaciones del voltaje umbral y la pendiente subumbral. Usando la función W de Lambert, además de una función de suavización para la transición entre las regiones de depleción y acumulación, se obtiene un modelo unificado de la densidad de carga, válido para todos los modos de operación del transistor. Se estudian también las dependencias entre los parámetros físicos del dispositivo y su impacto en su rendimiento. Se tienen en cuenta efectos importantes de canal corto y de cuantización. Se discuten también la simetría alrededor de Vds= 0 V, y la continuidad de la corriente de drenador en las derivadas de orden superior. El modelo fue validado mediante simulaciones TCAD numéricas y medidas experimentales.The main focus is on the development of an analytical, physics-based and predictive DC and AC compact model for nanoscale multiple-gate MOSFETs. The investigated devices are the standard inversion mode MOSFET and a new device concept called junctionless MOSFET. The model is derived in closed-from with the help of Poisson's equation and the conformal mapping technique by Schwarz-Christoffel. Equations for the calculation of the threshold voltage and subthreshold slope are derived. Using Lambert's W-function and a smoothing function for the transition between the depletion and accumulation region, an unified charge density model valid for all operating regimes is developed. Dependencies between the physical device parameters and their impact on the device performance are worked out. Important short-channel and quantization effects are taken into account. Symmetry around Vds = 0 V and continuity of the drain current at derivatives of higher order are discussed. The model is validated versus numerical TCAD simulations and measurement data

Dynamics of Excitons in Semiconductors

This thesis deals with the spectral and dynamic properties of excitons and excitonic resonances in semiconductors and semiconductor heterostructures. The intention is to expand the knowledge about excitons, their spectral properties, and their dynamics. The foundation for this are the results of several scientific publications in this field, which have been published as part of my doctoral studies. Chapter 1 introduces the topic by highlighting the tremendous importance of semiconductors and semiconductor-based devices for our modern society. In this context, the unique impact of excitons on the electro-optical properties of semiconductors is discussed and the relevance of a profound understanding of excitons, especially concerning the progressive miniaturization of semiconductor devices, is elaborated. Chapter 2 covers the physical principles of semiconductors and light-matter interaction, which form the theoretical backbone for the conducted experiments and their analysis. The applied experimental techniques are explained in Chapter 3. Particular attention is paid to optical pump-terahertz probe spectroscopy, which has been utilized intensively in this work and is one of the most important techniques to study excitons and their dynamics in semiconductors. Afterward, the experimental results are presented in chapters 4 to 7. Chapter 4 demonstrates via optical pump-terahertz probe spectroscopy that initially after a non-resonant optical excitation there is no exciton population present but only an electron-hole plasma in bulk germanium as well as in germanium and GaInAs quantum wells. In all cases, excitons are formed on a time scale of several tens to hundreds of picoseconds out of a pure electron-hole plasma. Several claims and observations on this topic in the scientific literature according to which a high proportion of excitons forms on a subpicosecond time scale are not supported for the samples investigated here [82, 188, 191]. While in bulk germanium a delayed exciton formation is observed, the exciton formation starts immediately after a non-resonant optical excitation in GaInAs quantum wells. Here, two different time periods, one of 14 ps and one of 344 ps, can be determined for the formation. Furthermore, theoretical predictions that at carrier densities far below the Mott density excitons form faster with increasing charge carrier density are confirmed in this chapter. Chapter 5 is focused exclusively on optical pump-terahertz probe experiments at bulk germanium. In section 5.1 an energetic splitting of the intraexcitonic 1s−2p resonance is detected. Soon before, this spectral behavior was predicted theoretically in germanium. Accordingly, the splitting of the intraexcitonic resonance is caused by the effective mass anisotropy of the L-valley electrons which leads to a splitting of the energy levels of the 2p states of the exciton. The ionization of an exciton population by strong terahertz pulses can be observed in section 5.2. Not only ionizes the exciton population for terahertz field strengths of 2.4 kV/cm completely, but also the spectral properties of the intraexcitonic transition are recorded as a function of field strength. It turns out that with increasing field strength of the terahertz pulse, thus for an increasing ionization of the exciton population, there is a broadening of the intraexcitonic 1s−2p resonance that is accompanied by a blueshift of up to 10 %. Section 5.3 investigates the scattering of free electrons and holes with an incoherent population of excitons. Utilizing two optical pulses an environment is created in which a cold population of excitons is surrounded by a hot electron-hole plasma. Both elastic and inelastic scattering processes increase the linewidth of the intraexcitonic resonance, while only inelastic scattering processes destroy the exciton population. This unique method enables the experimental differentiation between elastic and inelastic scattering processes in semiconductors for the first time, yielding an elastic scattering rate of 1.7·10^(−4) cm³/s and an inelastic scattering rate of 2.0·10^(−4) cm³/s. The coherent and incoherent dynamics of excitons in special semiconductor heterostructures, where the energetically most favorable states for electrons and holes are spatially separated by an intermediate barrier are studied in Chapter 6. Section 6.2 shows that excitonic states of spatially separated electrons and holes form a resonance in the linear absorption. This allows for the resonant excitation of these states so that the coherent lifetime of such excitonic charge-transfer states can be quantified and compared to that of regular excitonic states. The results of these investigations via four-wave mixing spectroscopy are presented in section 6.3. In addition to a beating between the respective states of the regular and the charge-transfer exciton, we find a decay time of the coherent polarization of the charge-transfer exciton of 0.4 ps. This decay is almost three times faster than the decay of the coherent polarization of the regular exciton from a GaInAs quantum well reference sample. This shorter coherent lifetime of charge-transfer excitons is attributed to additional scattering processes at the inner interface. The incoherent dynamics of charge-transfer excitons are examined in section 6.4 by optical pump-terahertz probe spectroscopy. Intraexcitonic transitions reveal that the charge-transfer excitons have a much lower 1s−2p transition energy of 3.2 meV than the regular excitons of the reference sample with 7 meV. The reason for this is the reduced Coulomb interaction due to the spatial separation of the charge carriers. Furthermore, we find a recombination time of the charge-transfer excitons of 2.5 ns, which is more than twice as long as that of regular excitons in the reference sample. After optical excitation conditions that are energetically above the resonance of the charge-transfer exciton, at first, the typical response of an electron-hole plasma is observed. In this plasma-like response, a shoulder forms on a time scale of several hundred picoseconds due to the incipient formation of a population of charge-transfer excitons. Within a few nanoseconds, a response develops which is nearly identical to the terahertz response shortly after resonant excitation conditions, indicating an almost pure population of charge-transfer excitons. The decay of the charge carriers shifts the energetic position of the intraexcitonic resonance on a nanosecond time scale from 2.2 meV to 3.2 meV. Such a density-dependent shift of the intraexcitonic resonance energy is not observed for regular excitons in GaInAs quantum well samples and is indicative of a more fermionic character of charge-transfer excitons. Finally, Chapter 7 is focused on the behavior of the excitonic absorption in optically excited semiconductor heterostructures. It turns out that the excitonic absorption of a quantum well can be spectrally narrowed after optical excitation, resulting in an increased absorption peak. It takes several tens to hundreds of picoseconds after the optical excitation until the linewidth narrowing occurs and, under suitable excitation conditions, enhances the excitonic absorption peak by more than 10 %. This unexpected behavior of the excitonic absorption can only be observed in those samples that allow for a spatial separation of electrons and holes. So far, there is no physical explanation for this remarkable phenomenon

Regional power systems planning: a state of the art assessment. Final report

The purpose of this report was to define regional power systems planning problems, the tools available and their shortcomings, and to document all of the above in a concise readable form. The approach consisted of a survey and literature search. The survey determined the tools being used by utilities, the tools they had rejected, and the tools they planned to try out. The literature search was conducted for the purpose of documenting the tools available, and performing a comparative analysis of these tools. The project included a mix of utility, university, and consulting organizations. Several organizations were consulted in the selection of the participants. A non-profit organization, The University of Oklahoma, was selected to manage the project. The results were reviewed in a series of four one day meetings by known authorities in each field. This report consists of the results of this project. Perhaps its major finding is that several aspects of the regional planning problem are not well defined, the roles of the various participants in regional planning is not clear, and certainly research is needed for the development of new methodology

Federal Register

Daily publication of the U.S. Office of the Federal Register contains rules and regulations, proposed legislation and rule changes, and other notices, including "Presidential proclamations and Executive Orders, Federal agency documents having general applicability and legal effect, documents required to be published by act of Congress, and other Federal agency documents of public interest" (p. ii). Table of Contents starts on page iii