SEMICONDUCTOR DEVICE FUNDAMENTALS

Transcription

1 SEMICONDUCTOR DEVICE FUNDAMENTALS Robert F. Pierret School of Electrical and Computer Engineering Purdue University Addison Wesley Longman Reading, Massachusetts Menlo Park, California New York Don Mills, Ontario Wokingham, England Amsterdam Bonn Sydney Singapore Tokyo Madrid San Juan Milan Paris

2 CONTENTS General Introduction xxi Part I Semiconductor Fundamentals 1 Chapter 1 Semiconductors: A General Introduction General Material Properties Composition Purity Structure Crystal Structure The Unit Cell Concept Simple 3-D Unit Cells Semiconductor Lattices Miller Indices Crystal Growth Obtaining Ultrapure Si Single-Crystal Formation Summary 19 Problems 19 Chapter 2 Carrier Modeling The Quantization Concept 23 Y 2.2 Semiconductor Models Bonding Model Energy Band Model Carriers 29 ~ ' Band Gap and Material Classification 31 Xj 2.3 Carrier Properties Charge Effective Mass Carrier Numbers in Intrinsic Material 34 ix

3 SEMICONDUCTOR DEVICE FUNDAMENTALS + H Chapter A Manipulation of Carrier Numbers Doping Carrier-Related Terminology 2.4 State and Carrier Distributions Density of States The Fermi Function Equilibrium Distribution of Carriers 2.5 Equilibrium Carrier Concentrations Formulas for n and p Alternative Expressions for n and p n ( and the np Product Charge Neutrality Relationship Carrier Concentration Calculations Determination of E F Carrier Concentration Temperature Dependence 2.6 Summary and Concluding Comments Problems Carrier Action V" A y- y 3.1 Drift Definition-Visualization Drift Current Mobility Resistivity Band Bending 3.2 Diffusion Definition-Visualization Hot-Point Probe Measurement Diffusion and Total Currents Diffusion Currents Total Currents Relating Diffusion Coefficients/Mobilities Constancy of the Fermi Level Current Flow Under Equilibrium Conditions Einstein Relationship 3.3 ^Recombination-Generation Definition-Visualization Band-to-Band Recombination

4 CONTENTS Xi R-G Center Recombination 105 Auger Recombination 107 Generation Processes Momentum Considerations R-G Statistics 110 Photogeneration 110 Indirect Thermal Recombination-Generation Minority Carrier Lifetimes 116 General Information 116 A Lifetime Measurement Equations of State Continuity Equations Minority Carrier Diffusion Equations Simplifications and Solutions Problem Solving 124 Sample Problem No Sample Problem No Supplemental Concepts Diffusion Lengths Quasi-Fermi Levels Summary and Concluding Comments 136 Problems 138 Chapter 4 Basics of Device Fabrication Fabrication Processes Oxidation Diffusion Ion Implantation Lithography Thin-Film Deposition 162 Evaporation 162 Sputtering 162 Chemical Vapor Deposition (CVD) Epitaxy 164 / / 4.2 Device Fabrication Examples 165.' pn Junction Diode Fabrication Computer CPU Process Flow Summary 174

5 Xii SEMICONDUCTOR DEVICE FUNDAMENTALS Rl Part I Supplement and Review 175 Alternative/Supplemental Reading List 175 Figure Sources/Cited References 177 Review List of Terms 178 Part I Review Problem Sets and Answers 179 Part MA pn Junction Diodes 193 Chapter 5 pn Junction Electrostatics Preliminaries Junction Terminology/Idealized Profiles Poisson's Equation Qualitative Solution The Built-in Potential (V bi ) The Depletion Approximation Quantitative Electrostatic Relationships Assumptions/Definitions Step Junction with V A = Solution for p 210 Solution for % 210 Solution for V 212 Solution for x n and x p Step Junction with V A * Examination/Extrapolation of Results Linearly Graded Junctions Summary 226 Problems 227 Chapter 6 pn Junction Diode: I-V Characteristics The Ideal Diode Equation Qualitative Derivation Quantitative Solution Strategy "241 General Considerations 241 Quasineutral Region Considerations 242 Depletion Region Considerations 243 Boundary Conditions 244

6 CONTENTS Xiii "Game Plan" Summary Derivation Proper Examination of Results 249 Ideal I-V 249 The Saturation Current 250 Carrier Currents 254 Carrier Concentrations Deviations from the Ideal Ideal Theory Versus Experiment Reverse-Bias Breakdown 263 Avalanching 264 Zener Process The R-G Current V A -» V bi High-Current Phenomena 277 Series Resistance 278 High-Level Injection Special Considerations Charge Control Approach Narrow-Base Diode 284 Current Derivation 284 Limiting Cases/Punch-Through Summary and Concluding Comments 288 Problems 289 Chapter 7 pn Junction Diode: Small-Signal Admittance Introduction Reverse-Bias Junction Capacitance General Information C-V Relationships Parameter Extraction/Profiling Reverse-Bias Conductance Forward-Bias Diffusion Admittance General Information Admittance Relationships Summary "Problems 324

7 XiV SEMICONDUCTOR DEVICE FUNDAMENTALS Chapter 8 pn Junction Diode: Transient Response Turn-Off Transient Introduction Qualitative Analysis The Storage Delay Time 333 Quantitative Analysis 333 Measurement General Information Turn-On Transient Summary 343 Problems 344 Chapter 9 Optoelectronic Diodes Introduction Photodiodes pn Junction Photodiodes p-i-n and Avalanche Photodiodes 352 p-i-n Photodiodes 352 Avalanche Photodiodes Solar Cells Solar Cell Basics Efficiency Considerations Solar Cell Technology LEDs General Overview Commercial LEDs LED Packaging and Photon Extraction 366 Part IIB BJTs and Other Junction Devices 369 Chapter 10 BJT Fundamentals Terminology Fabrication Electrostatics 378 s' 10.4 Introductory Operational Considerations Performance Parameters 382 Emitter Efficiency 382

8 CONTENTS XV Base Transport Factor 383 Common Base d.c. Current Gain 383 Common Emitter d.c. Current Gain Summary 385 Problems 385 Chapter 11 BJT Static Characteristics Ideal Transistor Analysis 389^ Solution Strategy 389 Basic Assumptions 389 Notation 390 Diffusion Equations/Boundary Conditions 390 Computational Relationships General Solution (W Arbitrary) 393 Emitter/Collector Region Solutions 393 Base Region Solution 394 Performance Parameters/Terminal Currents Simplified Relationships (W < L B ) 397 A/? B (x)inthebase 398 Performance Parameters Ebers-Moll Equations and Model Deviations from the Ideal Ideal Theory/Experiment Comparison Base Width Modulation Punch-Through Avalanche Multiplication and Breakdown 414 Common Base 414 Common Emitter Geometrical Effects 420 Emitter Area ^ Collector Area 420 Series Resistances 421 Current Crowding Recombination-Generation Current 422 -^ Graded Base Figures of Merit Modern BJT Structures Poly silicon Emitter BJT Heterojunction Bipolar Transistor (HBT) 429

9 XVi SEMICONDUCTOR DEVICE FUNDAMENTALS 11.4 Summary 432 Problems 433 Chapter 12 BJT Dynamic Response Modeling Small-Signal Equivalent Circuits Generalized Two-Port Model Hybrid-Pi Models Transient (Switching) Response Qualitative Observations Charge Control Relationships Quantitative Analysis 454 Turn-on Transient 454 Turn-off Transient Practical Considerations Summary 458 Problems 459 Chapter 13 PNPN Devices Silicon Controlled Rectifier (SCR) SCR Operational Theory Practical Turn-on/Turn-off Considerations Circuit Operation Additional Triggering Mechanisms Shorted-Cathode Configuration di/dt and dv/dt Effects Triggering Time Switching Advantages/Disadvantages Other PNPN Devices 474 Chapter 14 MS Contacts and Schottky Diodes 477 "fv Ideal MS Contacts 477 -j 14.2 Schottky Diode Electrostatics 483 _^ Built-in Voltage 483 p, %, V 485 Depletion Width I-V Characteristics a.c. Response 493

10 CONTENTS XVii Transient Response 496 V 14.3 Practical Contact Considerations Rectifying Contacts Ohmic Contacts Summary 500 Problems 501 R2 Part II Supplement and Review 505 Alternative/Supplemental Reading List 505 Figure Sources/Cited References 506 Review List of Terms 507 Part II Review Problem Sets and Answers 508 Part III Field Effect Devices 523 Chapter 15 Field Effect Introduction The J-FET and MESFET General Introduction J-FET Introduction Qualitative Theory of Operation Quantitative I D V D Relationships a.c. Response MESFET General Information Short-Channel Considerations 552 Variable Mobility Model 553 Saturated Velocity Model 554 Two-Region Model Summary 557 Problems 557 Chapter 16 MOS Fundamentals 563 X 16.1 Ideal Structure Definition 563 y 16.2 Electrostatics Mostly Qualitative Visualization Aids 565 Energy Band Diagram 565 Block Charge Diagrams 566

11 XVIII SEMICONDUCTOR DEVICE FUNDAMENTALS Effect of an Applied Bias General Observations Specific Biasing Regions \^ 16.3 Electrostatics Quantitative Formulation / Semiconductor Electrostatics Preparatory Considerations Delta-Depletion Solution Gate Voltage Relationship \i 16.4 Capacitance-Voltage Characteristics Theory and Analysis Qualitative Theory Delta-Depletion Analysis Computations and Observations Exact Computations Practical Observations 16.5 Summary and Concluding Comments Problems Chapter 17 MOSFETs The Essentials 7S 17.1 Qualitative Theory of Operation v Quantitative / D -V D Relationships Preliminary Considerations Threshold Voltage Effective Mobility Square-Law Theory Bulk-Charge Theory Charge-Sheet and Exact-Charge Theories r7r3 a:c. Response Small-Signal Equivalent Circuits Cutoff Frequency Small-Signal Characteristics 17.4 Summary Problems Chapter 18 Nonideal MOS 18.1 Metal-Semiconductor Workfunction Difference

12 CONTENTS xix \ \ \ \ 18.2 Oxide Charges General Information Mobile Ions The Fixed Charge Interfacial Traps Induced Charges Radiation Effects Negative-Bias Instability A V c Summary 18.3 MOSFET Threshold Considerations Problems V T Relationships Threshold, Terminology, and Technology Threshold Adjustment Back Biasing Threshold Summary Chapter 19 Modern FET Structures 19.1 Small Dimension Effects Introduction Threshold Voltage Modification Short Channel Narrow Width Parasitic BJT Action Hot-Carrier Effects Oxide Charging Velocity Saturation Velocity Overshoot/Ballistic Transport 19.2 Select Structure Survey Problems MOSFET Structures LDD Transistors DMOS Buried-Channel MOSFET SiGe Devices SOI Structures MODFET(HEMT)

13 XX SEMICONDUCTOR DEVICE FUNDAMENTALS R3 Part III Supplement and Review 713 Alternative/Supplemental Reading List 713 Figure Sources/Cited References 714 Review List of Terms 717 Part III Review Problem Sets and Answers 718 Appendices 733 Appendix A Elements of Quantum Mechanics 733 A. 1 The Quantization Concept 733 A. 1.1 Blackbody Radiation 733 A. 1.2 The Bohr Atom 735 A. 1.3 Wave-Particle Duality 737 A.2 Basic Formalism 739 A. 3 Electronic States in Atoms 741 A.3.1 The Hydrogen Atom 741 A.3.2 Multi-Electron Atoms 744 Appendix B MOS Semiconductor Electrostatics Exact Solution 749 Definition of Parameters 749 Exact Solution 750 Appendix C MOS C-V Supplement 753 Appendix D MOS I-V Supplement 755 Appendix E List of Symbols 757 Appendix M MATLAB Program Script 771 Exercise 10.2 (BJT_Eband) 771 Exercise 11.7 (BJT) and Exercise (BJTplus) 774 Exercise 16.5 (MOS^CV) 778 Index 781