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Velocity saturation

About: Velocity saturation is a(n) research topic. Over the lifetime, 1099 publication(s) have been published within this topic receiving 21345 citation(s). more


Journal ArticleDOI: 10.1016/S0379-6779(02)00398-3
Norbert Karl1Institutions (1)
13 Mar 2003-Synthetic Metals
Abstract: To understand charge carrier transport in organic semiconductors the magnitude and anisotropy, as well as the temperature and eventual electric field dependence of the electron and of the hole mobility are fundamental parameters. A number of technical applications require high mobilities. A brief review is given on different experimental methods that can either directly measure charge carrier mobilities, or at least lead to an estimate. For high purity single crystals, a steep increase of mobilities towards low temperature with the consequence of nonlinear transport and final velocity saturation at elevated electric fields has been found and traced back to temperature-dependent electron and hole masses approaching the free electron mass at low temperature. This, and additional recent reports in literature on ultrahigh mobilities—with a number of exciting consequences, such as integer and fractional quantum Hall effect and even superconductivity in such materials as anthracene, tetracene, pentacene, and C60—are clear indications of band transport. With rising temperature electron–phonon coupling, and therefore the effective masses, increase and coherent band transport is gradually destroyed; polaron-hopping transport evolves as a parallel channel and dominates at sufficiently high temperature. For crystals with orientational disorder of the molecules band transport is precluded. more

Topics: Saturation velocity (61%), Charge carrier (60%), Electron mobility (59%) more

557 Citations

Journal ArticleDOI: 10.1109/16.974760
Mark Lundstrom1, Zhibin Ren1Institutions (1)
Abstract: The device physics of nanoscale MOSFETs is explored by numerical simulations of a model transistor. The physics of charge control, source velocity saturation due to thermal injection, and scattering in ultrasmall devices are examined. The results show that the essential physics of nanoscale MOSFETs can be understood in terms of a conceptually simple scattering model. more

Topics: Velocity saturation (57%), MOSFET (54%), Transistor (51%) more

523 Citations

Open accessBook
27 Oct 2005-
Abstract: PART I INTRODUCTION TO SEMICONDUCTORS 1 lNTRODUCTION TO CRYSTALS AND CURRENT CARRIERS IN SEMICONDUCTORS, THE ATOMIC-BOND MODEL 1.1 INTRODUCTION TO CRYSTALS 1.1.1 Atomic Bonds 1.1.2 Three-Dimensional Crystals 1.1.3 Two-Dimensional Crystals: Graphene and Carbon Nanotubes 1.2 CURRENT CARRIERS 1.2.1 Two Types of Current Carriers in Semiconductors 1.2.2 N*Type and P-Type Doping 1.2.3 Electroneutrality Equation 1.2.4 Electron and Hole Generation and Recombination in Thermal Equilibrium 1.3 BASICS OF CRYSTAL GROWTH AND DOPING TECHNIQUES 1.3.1 Crystal-Growth Techniques 1.3.2 Doping Techniques Summary Problems Review Questions 2 THE ENERGY-BAND MODEL 12.1 ELECTRONS AS WAVES 2.1.1 De Broglie Relationship Between Particle and Wave Properties 2.1.2 Wave Function and Wave Packet 2.1.3 Schrodinger Equation 2.2 ENERGY LEVELS IN ATOMS AND ENERGY BANDS IN CRYSTALS 2.2.1 Atomic Structure 2.2.2 Energy Bands in Metals 2.2.3 Energy Gap and Energy Bands in Semiconductors and Insulators 12.3 ELECTRONS AND HOLES AS PARTICLES 2.3.1 Effective Mass and Real E-k Diagrams 2.3.2 The Question of Electron Size: The Uncertainty Principle 2.3.3 Density of Electron States 2.4 POPULATION OF ELECTRON STATES, CONCENTRATIONS OF ELECTRONS A:"D HOLES 2.4.1 Fermi-Dirac Distribution 2.4.2 Maxwell-Boltzmann Approximation and Effective Density of States 2.4.3 Fermi Potential and Doping 2.4.4 Nonequilibrium Carrier Concentrations and Quasi-Fermi Levels Summary Problems Review Questions 3 DRIFT 3.1 ENERGY BANDS WITH APPLIED ELECTRIC FIELD 3.1.1 Energy-Band Presentation of Drift Current 3.1.2 Resistance and Power Dissipation due to Carrier Scattering 3.2 OHM'S LAW, SHEET RESISTANCE, AND CONDUCTIVITY 3.2.1 Designing Integrated-Circuit Resistors 3.2.2 Differential Form of Ohm's Law 3.2.3 Conductivity Ingredients 3.3 CARRIER MOBILITY 3.3.1 Thermal and Drift Velocities 3.3.2 Mobility Definition 3.3.3 Scattering Time and Scattering Cross Section 3.3.4 Mathieson's Rule 3.3.5 Hall Effect Summary Problems Review Questions 4 DlFFUSION 4.1 DIFFUSION-CURRENT EQUATION 4.2 DIFFUSION COEFFICIENT 4.2.1 Einstein Relationship L4.2.2 Haynes-Shockley Experiment 4.2.3 Arrhenius Equation 4.3 BASIC CONTINUITY EQUATION Summary Problems Review Questions 5 GENERATION AND RECOMBINATION 5.1 GENERATION AND RECOMBINATION MECHANISMS 5.2 GENERAL FORM OF THE CONTINUITY EQUATION 5.2.1 Recombination and Generation Rates 5.2.2 Minority-Carrier Lifetime 5.2.3 Diffusion Length 5.3 GENERATION AND RECOMBINATION PHYSICS AND SHOCKLEYREAD- HALL (SRH) THEORY 5.3.1 Capture and Emission Rates in Thermal Equilibrium 5.3.2 Steady-State Equation for the Effective Thermal Generation/Recombination Rate 5.3.3 Special Cases 5.3.4 Surface Generation and Recombination Summary Problems Review Questions PART II FUNDAMENTAL DEVICE STRUCTURES 6 JUNCTIONS 6.1 P-N JUNCTION PRINCIPLES 6.1.1 p-~ Junction in Thermal Equilibrium 6.1.2 Reverse-Biased P-N Junction 6.1.3 Forward-Biased P-K Junction 6.1.4 Breakdown Phenomena 6.2 DC MODEL 6.2.1 Basic Current-Voltage (I-V) Equation 6.2.2 Important Second-Order Effects 6.2.3 Temperature Effects 6.3 CAPACITA CE OF REVERSE-BIASED P-:-I JUNCTION 6.3.1 C-V Dependence 6.3.2 Depletion-Layer Width: Solving the Poisson Equation 6.3.3 SPICE Model for the Depletion-Layer Capacitance 6.4 STORED-CHARGE EFFECTS 6.4.1 Stored Charge and Transit Time 6.4.2 Relationship Between the Transit Time and the Minority-Carrier Lifetime 6.4.3 Switching Characteristics: Reverse-Recovery Time 6.5 METAL-SEMICONDUCTOR CONTACT 6.5.1 Schottky Diode: Rectifying Metal-Semiconductor Contact 6.5.2 Ohmic Metal-Semiconductor Contacts Summary Problems Review Questions 7 MOSFET 7.1 MOS CAPACITOR 7.1.1 Properties of the Gate Oxide and the Oxide-Semiconductor Interface 7.1.2 C-V Curve and the Surface-Potential Dependence on Gate Voltage 7.1.3 Energy-Band Diagrams 7.1.4 Flat4Band Capacitance and Debye Length 7.2 MOSFET PRINCIPLES B.1.1 MOSFET Structure 7.2.2 MOSFET as a Voltage-Controlled Switch B.1.3 The Threshold Voltage and the Body Effect B.1.4 MOSFET as a Voltage-Controlled Current Source: Mechanisms of Current Saturation 7.3 PRINCIPAL CURRENT-VOLTAGE CHARACTERISTICS AND EQUATIONS 7.3.1 SPICE LEVEL 1 Model 7.3.2 SPICE LEVEL 2 Model 7.3.3 SPICE LEVEL 3 Model: Principal Effects 7.4 SECO:\D-OROER EFFECTS 7.4.1 Mobility Reduction with Gate Voltage 7.4.2 Velocity Saturation (Mobility Reduction with Drain Voltage) 7.4.3 Finite Output Resistance 7.4.4 Threshold-Voltage-Related Short-Channel Effects 7.4.5 Threshold Voltage Related Narrow-Channel Effects 7.4.6 Subthreshold Current 7.5 Nanoscale MOSFETs 7.5.1 Down-Scaling Benefits and Rules 7.5.2 Leakage Currents 7.5.3 Advanced MOSFETs 7.6 MOS-BASED MEMORY DEVICES 7.6.1 1C1T DRAM Cell 7.6.2 Flash-Memory Cell Summary Problems Review Questions 8 BJT 8.1 B.JT PRINCIPLES 8.1.1 BJT as a Voltage-Controlled Current Source 8.1.2 BJT Currents and Gain Definitions 8.1.3 Dependence of ? and ? Current Gains on Technological Parameters 8.1.4 The Four Modes of Operation: BJT as a Switch 8.1.5 Complementary BJT 8.1.6 BJT Versus MOSFET 8.2 PRINCIPAL CURRENT-VOLTAGE CHARACTERISTICS, EBERE-MOLL MODEL IN SPICE 8.2.1 Injection Version 8.2.2 Transport Version 8.2.3 SPICE Version 8.3 SECOND*ORDER EFFECTS 8.3.1 Early Effect: Finite Dynamic Output Resistance 8.3.2 Parasitic Resistances 8.3.3 Dependence of Common-Emitter Current Gain on Transistor Current: Low-Current Effects 8.3.4 Dependence of Common-Emitter Current Gain on Transistor Current: Gummel-Poon Model for High-Current Effects 8.4 HETEROJUNCTION BIPOLAR TRANSISTOR Summary Problems Review Questions PART III SUPPLEMENTARY TOPICS 9 PHYSICS OF NANOSCALE DEVICES 9.1 SINGLE-CARRIER EVENTS 9.1.1 Beyond the Classical Principle of Continuity 9.1.2 Current-Time Form of Uncertainty Principle 9.1.3 Carrier-Supply Limit to Diffusion Current 9.1.4 Spatial Uncertainty 9.1.5 Direct Nonequilibrium Modeling of Single-Carrier Events 9.2 TWO-DIMENSIONAL TRANSPORT IN MOSFETs AND HEMTs 9.2.1 Quantum Confinement 9.2.2 HEMT Structure and Characteristics 9.2.3 Application of Classical MOSFET Equations to Two-Dimensional Transport in MOSFETs and HEMTs 9.3 ONE-DIMENSUIONAL TRANSPORT IN NANOWIRES AND CARBON NANOTUBES 9.3.1 Ohmic Transport in Nanowire and Carbon-Nanotube FETs 9.3.2 One-Dimensional Ballistic Transport and the Quantum Conductance Limit Summary Problems Review Questions 10 DEVICE ELECTRONICS, EQUIVALENT CIRCUITS A D SPICE PARAMETERS 10.l DIODES 10.1.1 Static Model and Parameters in SPICE 10.1.2 Large-Signal Equivalent Circuit in SPICE 10.1.3 Parameter Measurement 10.1.4 Small-Signal Equivalent Circuit 10.2 MOSFET 10.2.1 Static Model and Parameters LEVEL 3 in SPICE 10.2.2 Parameter Measurement 10.2.3 Large-Signal Equivalent Circuit and Dynamic Parameters in SPICE 10.2.4 Simple Digital ~1od.el 10.2.5 Small-Signal Equivalent Circuit 10.3 BJT 10.3.1 Static Model and Parameters: Ebers-Moll and Gummel-Poon Levels in SPICE 10.3.2 Parameter Measurement 10.3.3 Large-Signal Equivalent Circuit and Dynamic Parameters in SPICE 10.3.4 Small-Signal Equivalent Circuit Summary Problems Review Questions 11 PHOTONIC DEVICES 11.1 LIGHT EMITTING DIODES (LED) 11.2 PHOTODETECTORS AND SOLAR CELLS 11.2.1 Biasing for Photodetector and Solar-Cell Applications 11.2.2 Carrier Generation in Photodetectors and Solar Cells 11.2.3 Photocurrent Equation 11.3 LASERS 11.3.1 Stimulated Emission, Inversion Population, and Other Fundamental Concepts 11.3.2 A Typical Heterojunction Laser Summary Problems Review Questions 12 JFET AND MESFET 12.1 JFET 12.1.1 JFET Structure 12.1.2 JFET Characteristics 12.1.3 SPICE Model and Parameters 12.2 MESFET 12.2.1 MESFET Structure 12.2.2 MESFET Characteristics 12.2.3 SPICE Model and Parameters Summary Problems Review Questions 13 POWER DEVICES 13.1 POWER DIODES 13.1.1 Drift Region in Power Devices 13.1.2 Switching Characteristics 13.1.3 Schottky Diode 13.2 POWER MOSFET 13.3 IGBT 13.4 THYRISTOR Summary Problems Review Questions more

Topics: Bipolar junction transistor (59%), Power semiconductor device (58%), Power MOSFET (57%) more

436 Citations

Open accessJournal ArticleDOI: 10.1063/1.3483130
Abstract: We examine mobility and saturation velocity in graphene on SiO2 above room temperature (300-500 K) and at high fields (~1 V/um). Data are analyzed with practical models including gated carriers, thermal generation, "puddle" charge, and Joule heating. Both mobility and saturation velocity decrease with rising temperature above 300 K, and with rising carrier density above 2x10^12 cm^-2. Saturation velocity is >3x10^7 cm/s at low carrier density, and remains greater than in Si up to 1.2x10^13 cm^-2. Transport appears primarily limited by the SiO2 substrate, but results suggest intrinsic graphene saturation velocity could be more than twice that observed here. more

Topics: Saturation velocity (69%), Velocity saturation (68%), Joule heating (50%)

377 Citations

Journal ArticleDOI: 10.1016/0038-1101(85)90100-5
G. Baccarani1, M.R. Wordeman1Institutions (1)
Abstract: Electron dynamics in silicon is investigated by means of improved momentum- and energy-balance equations including particle diffusion and heat flux. The resulting system of partial differential equations is numerically solved in a variety of field configurations including strong discontinuities, in order to enhance velocity overshoot effects. It is found that diffusion, usually neglected in previous studies, plays a major role, and considerably modifies the features of the velocity vs distance curve, leading to an increase of the carrier drift velocity in the low-field region, i.e. before experiencing the effect of the strong field. In addition, it is found that, in order to take full advantage of velocity overshoot effects in MOSFET's, a structure must be designed having the strongest possible field at the source-end of the channel, where carrier density is controlled by the gate. more

Topics: Velocity overshoot (71%), Velocity saturation (64%), Drift velocity (63%) more

355 Citations

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Topic's top 5 most impactful authors

Razali Ismail

29 papers, 271 citations

Vijay K. Arora

23 papers, 271 citations

Michael Shur

16 papers, 362 citations

Mohammad Taghi Ahmadi

8 papers, 88 citations

Hadi Arabshahi

6 papers, 21 citations

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