Silicon Photonics Fundamentals and Devices

M. Jamal Deen completed a BSc degree at the University of Guyana (Guyana) and a PhD in Electrical Engineering and Applied Physics at Case Western Reserve University (USA). Professor Deen has been an assistant professor at Lehigh University, Bethlehem (USA) and was professor in the School of Engineering Science, Simon Fraser University, Vancouver (Canada). In 1999, he assumed his current position as Professor of Electrical and Computer Engineering, McMaster University, Hamilton (Canada). His current research interests include physics, modeling, reliability and parameter extraction of semiconductor devices; optical detectors and receivers, polymers and organic semiconductor devices, and low power, low-noise, high-frequency circuits. He is a Distinguished Lecturer of the IEEE- Electron Device Society, was awarded the 2002 Thomas D. Callinan Award from the Electrochemical Society, the Distinguished Researcher award, Province of Ontario and a Humboldt Research Award from the Alexander von Humboldt Foundation in 2006. In September 2008, he was awarded the prestigious Thomas W. Eadie medal by the Royal Society of Canada for his work on the modeling and noise of electronic and optoelectronic devices, with particular reference to silicon transistors and high-speed photodetectors.

Prasanta Kumar Basu obtained his BSc and his PhD from the University of Calcutta (India). He worked in the Institute of Radio Physics and Electronics, as a lecturer, then as a reader and finally as a professor. He served as the Head of the Department and he is now the Programme Coordinator of the Centre of Advanced Study in Radio Physics and Electronics at the University of Calcutta. Professor Basu worked as a Postdoctoral Fellow at the Catholic University, Leuven, Belgium, as an Alexander von Humboldt Fellow in Wuerzburg University, Germany and has been a visiting professor at McMaster University, Hamilton, Canada several times. Professor Basu’s research interests include semiconductor physics and devices, optoelectronics and optical communication, nanoelectronics and nanophotonics. He has more than 100 research publications in refereed journals and has authored a book Theory of Optical Processes in Semiconductors: Bulk and Microstructures.

Preface xvii

1 Introduction to Silicon Photonics 1

1.1 Introduction 1

1.2 VLSI: Past, Present, and Future Roadmap 2

1.3 The Interconnect Problem in VLSI 3

1.4 The Long-Haul Optical Communication Link 4

1.5 Data Network 7

1.6 Conclusions 7

1.7 Scope of the Book 8

2 Basic Properties of Silicon 11

2.1 Introduction 11

2.2 Band Structure 12

2.3 Density-of-States Function 17

2.4 Impurities 19

2.5 Alloys of Silicon and Other Group IV Elements 21

2.6 Heterojunctions and Band Lineup 23

2.7 Si-Based Heterostructures 24

2.8 Direct GAP: Ge/SiGeSn Heterojunctions 33

3 Quantum Structures 41

3.1 Introduction 41

3.2 Quantum Wells 41

3.3 Quantum Wires and Dots 48

3.4 Superlattices 50

3.5 Si-Based Quantum Structures 52

3.6 Effect of Electric Field 56

4 Optical Processes 61

4.1 Introduction 61

4.2 Optical Constants 61

4.3 Basic Concepts 64

4.4 Absorption Processes in Semiconductors 66

4.5 Fundamental Absorption in Direct GAP 66

4.6 Fundamental Absorption in Indirect GAP 73

4.7 Absorption and Gain 77

4.8 Intervalence Band Absorption 79

4.9 Free-carrier Absorption 80

4.10 Recombination and Luminescence 82

4.11 Nonradiative Recombination 86

4.12 Excitonic and Impurity Absorption 91

5 Optical Processes in Quantum Structures 97

5.1 Introduction 97

5.2 Optical Processes in QWs 98

5.3 Intersubband Transitions 105

5.4 Excitonic Processes in QWs 109

5.5 Effect of Electric Fields 114

5.6 Optical Processes in QWRs 118

5.7 Optical Processes in QDS 119

6 Light Emitters in Si 123

6.1 Introduction 123

6.2 Basic Theory of Light Emission 124

6.3 Early Efforts: Zone Folding 125

6.4 Band Structure Engineering Using Alloys 126

6.5 Quantum Confinement 129

6.6 Imputities in Silicon 134

6.7 Stimulated Emission: Prospect 139

6.8 Intersubband Emission 143

6.9 Tensile-Strained Ge Layers 146

7 Si Light Modulators 151

7.1 Introduction 151

7.2 Physical Effects 152

7.3 Electrorefraction in Silicon 156

7.4 Thermo-Optic Effects in Si 158

7.5 Modulators: Some Useful Characteristics 159

7.6 Modulation Bandwidth under Injection 160

7.7 Optical Structures 161

7.8 Electrical Structures 164

7.9 High-Bandwidth Modulators 168

7.10 Performance of EO Modulators 170

8 Silicon Photodetectors 175

8.1 Introduction 175

8.2 Optical Detection 176

8.3 Important Characteristics of Photodetectors 180

8.4 Examples of Types of Photodetectors 187

8.5 Examples of Photodiodes in Standard Silicon Technology 192

8.6 Phototransistors in Standard Silicon Technology 196

8.7 CMOS and BiCMOS 197

8.8 Silicon-on-Insulator (SOI) 198

8.9 Photodetectors Using Heteroepitaxy 202

9 Raman Lasers 219

9.1 Introduction 219

9.2 Raman Scattering: Basic Concepts 220

9.3 Simplified Theory of Raman Scattering 222

9.4 Raman Effect in Silicon 224

9.5 Raman Gain Coefficient 224

9.6 Continuous-Wave Raman Laser 228

9.7 Further Developments 230

10 Guided Lightwaves: Introduction 233

10.1 Introduction 233

10.2 Ray Optic Theory for Light Guidance 233

10.3 Reflection Coefficients 234

10.4 Modes of a Planar Waveguide 235

10.5 Wave Theory of Light Guides 238

10.6 3D Optical Waveguides 244

10.7 Loss Mechanisms in Waveguides 252

10.8 Coupling to Optical Devices 257

10.9 Tapers 261

11 Principle of Planar Waveguide Devices 267

11.1 Introduction 267

11.2 Model for Mode Coupling 267

11.3 Directional Coupler 270

11.4 Distributed Bragg Reflector 273

11.5 Some Useful Planar Devices 277

12 Waveguides for Dense Wavelength-Division Multiplexing (DWDM) Systems 293

12.1 Introduction 293

12.2 Structure and Operation of AWGs 294

12.3 AWG Characteristics 297

12.4 Methods for Improving Performance 300

12.5 Applications of AWGs 303

12.6 PHASAR-Based Devices on Different Materials 306

12.7 Echelle Grating 307

13 Fabrication Techniques and Materials Systems 311

13.1 Introduction 311

13.2 Planar Processing 312

13.3 Substrate Growth and Preparation 312

13.4 Material Modification 318

13.5 Etching 322

13.6 Lithography 326

13.7 Fabrication of Waveguides 328

13.8 Grating Formation Process 331

13.9 Materials Systems for Waveguide Formation 334

Problems 348

References 349

Further Reading 352

Appendix A: k.p Method 355

Appendix B: Values of Parameters 371

Index

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