Fundamentals of Infrared Detector Operation and Testing

Transcription

1 Fundamentals of Infrared Detector Operation and Testing JOHN DAVID VINCENT Santa Barbara Research Center Goleta, California WILEY A Wiley-Interscience Publication John Wiley & Sons New York I Chichester I Brisbane I Toronto I Singapore

2 Contents UNIT 1 DETECTORS AND DETECTOR OPERATION Chapter 1. Introduction and Overview Infrared Radiation Heat Transfer Thermal Detectors Planck's Law Waves and Photons Quantum (Photon) Detectors IR Detectors as Transducers Detector Parameters: Definitions Responsivity Noise Signal-to-Noise Ratio Noise Equivalent Power Specific Detectivity Linearity and Saturation Frequency Response Spatial Considerations Crosstalk References Suggested Reading Problems Chapter 2. Detector Types, Mechanisms, and Operation Thermal Detectors Bolometers Photon (Quantum) Detectors Carrier Generation Spectral Response of Photon Detectors Temperature Dependence of Semiconductor Carrier Density Types of Photon Detectors Diodes and Photovoltaic Detectors Photoconductive Detectors 40 t

3 XIV CONTENTS 2.3 Detector Operation Cooling Photoconductor Biasing Photovoltaic Circuits Detector Parameters: Models and Predictions Current Equations Responsivity Noise Noise Equivalent Power Specific Detectivity Modulation Transfer Function Detector Materials and Performance Predictions Photovoltaic Indium Antimonide (InSb) f PV Mercury-Cadmium-Telluride (HgCdTe) Schottky Barrier Detectors; Platinum Silicide Doped Germanium and Silicon PC Mercury-Cadmium-Telluride (HgCdTe) Lead Salts 79 References 81 Suggested Reading 82 Problems 83 Detector Types, Mechanism 85 Detector Operation 84 Detector Figure of Merit 84 Chapter 3 Radiometry The General Method The Incremental Limit Extensions Nomenclature and Notation Blackbodies, Graybodies, and Emissivity Spectral Content Planck's Law for Spectral Exitance The Spectral Integral Accuracy of Radiometric Calculations Signal from a Broad Spectral Source Response per Degree Difference in Scene Temperature Spatial Integral Solid Angles Simple and Projected Solid Angles 132

4 CONTENTS xv Solid Angles for Specific Geometries More Complicated Geometries: Angle Factors Time Dependence (Modulation) Fourier Analysis of Waveforms Modulation Factors Sine-Wave Modulation Examples and Cases of Special Interest Background in a Test Dewar Narrow Bandpass Filter Background in a Test Dewar Wide Bandpass Filter Incidence from a Blackbody Test Set (All Wavelengths) Sunlight on the Earth Sunlight Reflected from a Window Moonlight on the Earth Sterance from the Earth FORTRAN Computer Code for Radiometric Calculations AMDOF: Prints Table of Modulation Factors AMODF2: Generates Case II Modulation Factors AMODF3: Generates Case III Modulation Factors AFLUX: Generates rms Incidences FLUX TABLES: Prints Tables of Blackbody Incidance 161 References 162 Suggested Reading 163 Problems 164 General Radiometry 164 Spectral Content 165 The Spatial Integral 168 Modulation 169 Chapter 4 The Test Set Types of Test Sets Blackbody and Dewar Chambers Focused Optics: Spot and Line Scanners 172

5 XVI CONTENTS Spectrometers Special Applications Design and Documentation Requirement Definition Design Review Scale Drawings Emissivity and Reflectivity in the Infrared The Blackbody Test Set Blackbodies Mounting of the Blackbody Measurement of Blackbody Temperature Measurement and Documentation of Blackbody Aperture Diameters Shutters and Choppers Between the Source and Detector Folding Mirrors Orientation of Knife-Edged Apertures and Baffles Unwanted Reflecting Surfaces Accuracy Required in Measuring Detectorto-Blackbody Distances Dewars Design Decisions for Background Reduction Effect of Ambient Temperature on Background Field of View Baffles Windows and Filters Test Set Evaluation and Troubleshooting The Radiometric Calibration Problem Radiometric Standards Radiometric Verification 205 References 207 Suggested Reading 209 IR Reflectance of Optical Blacks 209 IR Reflectance of "Mirrors" (High- Reflectivity Coatings) 210 Blackbody Theory and Design 211 Problems 212 Chapter 5 Detector Testing Preliminaries Information Needed 214

6 5.1.2 Test Planning Test Procedure Pretest Operations V-I Curves Equipment Used for V-I Curves Analysis of V-I Curves for Photovoltaic Detectors V-I Data for Photoconductors Noise Digital Calculations Error in Digital Noise Measurements Analog Measurements of Noise: Meters and Their Errors Bandwidth for Noise Calculations Characterization of Low-Frequency Noise Blackbody Signal and Responsivity Blackbody Test Set Blackbody Responsivity Optimization of Bias Voltage Accuracy of Blackbody Responsivity Data Effect of Sample Size on Signal Uncertainty Effective Area Confidence-Building Techniques Hints for Data Reduction Analysis of Detector Current, Signal, and Noise Data Frequency Response Response versus Frequency Time Constant and Corner Frequency Low-Background Testing Background Reduction Methods Background Leaks Low-Signal Problems High-Impedance Electronics Frequency Response Spectral Measurements Relative Spectral Response Absolute Spectral Response Values Effective Incidence and Blackbody-to-Peak Conversion Reflectance and Transmittance Measurements 261

7 XVUl CONTENTS 5.10 Spatial Measurements Spot Scans Modulation Transfer Function Crosstalk Test Reports 265 References 267 Suggested Reading 268 Problems 268 UNIT 2 RELATED SKILLS 273 Chapter 6. Science and Measurements Units Basic Estimate Rejecting Data Uncertainty Experimental Error Systematic Errors Random Errors Illegitimate Errors Validity of the Model Estimating Uncertainties Subjective or Intuitive Estimate of Uncertainty The Probability of Blunders Estimating the Magnitude of Systematic Errors Estimating the Magnitude of Random Errors Probability An Introduction to Probability: Normal Curve of Error Standard Deviations for Common Best Estimates Example of Standard Deviations for Two Data Sets Propagation of Errors Direct Method Shortcuts in Estimating Error Propagation Probable Total Error

8 CONTENTS xix 6.6 Reporting Uncertainties The Ethics of Scientific Work Independent Checks Agressive Learning A Note of Caution The Overall Test Task Designing the Test Data Review and Interpretation Presentation of Results Graphing 299 References 300 Suggested Reading 300 Problems 301 Chapter 7. Cryogenics Cryogens Heat of Vaporization Enthalpy Storage of Cryogens; Dewars Transfer of Cryogens Continual Transfer Systems Liquid Level Sensors Thermal Properties of Solids Thermal Expansion Heat Conduction; Thermal Conductivity Heat Capacity; Specific Heat Electrical Analogs Dewar Design Refrigerators Joule-Thompson Liquefier Thermoelectric Coolers Radiation Coolers Temperature Measurement Temperature Sensors Mounting of Cryogenic Thermometers Cryogenics and Safety 331 References 333 Suggested Reading 335 Cryogenics: General and Engineering 335 Handbook and Tabular Material 335 Problems 337

9 XX CONTENTS Chapter 8. Vacuum Practices Introduction Units Conversion between Molecular Density and Pressure Gauges Thermocouple Gauges Ion Gauges Pumps Oil Sealed Rotary Pumps Turbomolecular Pumps Diffusion Pumps Cold Traps Sorption Pumps Ion Pumps Manifolds Operation of a Typical Multiport Vacuum Station Pumping Dynamics Vocabulary and Units Mean Free Path Conductance Formulas Time to Pump a Perfectly Clean Volume Outgassing Time to Pump a Real System Reduction of Outgassing Permanent Vacuum Leaks Leak Detection Adequate Vacuum for Test Dewars Heat Conduction by Gases Allowable Condensation Leaks and Outgassing Pumping Dynamics Condensation Vacuum and Safety 364 References 365 Suggested Reading 365 Problems 366 Chapter 9. Optics and Optical Materials Infrared Optical Materials Selection of Window Materials 369

10 CONTENTS xxi Required Thickness for Vacuum Windows Index of Refraction Dispersion Transmittance of Windows Geometrical Optics Angle of Reflection Refraction Snell's Law Optical Thickness Reflectance and Transmittance Calculations Reflectance and Transmittance of Nonabsorbing Materials Reflectance at Other than Normal Incidence Absorption in Optical Materials Mirrors and Blacks Bidirectional Reflectance Distribution Function Interference Effects Antireflection Coatings Spectral Filters Spectral Transmittance Measurements Neutral Density Filters Transmittance of Two Filters in Series Diffraction Resolution Limits and Criteria Resolution of the Human Eye 395 References 397 Suggested Reading 397 Catalogues and Handbooks from Vendors 398 Problems 399 Chapter 10. Electronics Passive Components Resistors Capacitors Transistors and Their Use as Amplifiers Bipolar Junction Transistors Junction Field-Effect Transistors Metal-Oxide Field-Effect Transistors Amplifiers Feedback Theory and Stability Operational Amplifiers Amplifiers for High-Impedance Detectors 433

11 XXII CONTENTS Amplifiers for Intermediate Impedance Detectors Amplifiers for Low-Impedance Detectors Laboratory Testing Grounding Laboratory Equipment 442 References 444 Suggested Reading 445 Problems 445 APPENDIXES 449 Appendix A Symbols and Abbreviations 451 Appendix В Glossary 455 Appendix С Decibel Convention 457 Appendix D Characterization of Semiconductor Materials 1. Resistance Measurements 1.1 Rectangular Bar 1.2 Four-Lead Method 1.3 Hall Bar 2. Wafer Measurements 3. Hall Effect 4. Energy Level and Band Gap Determination 5. Lifetime References 468 Index 469