SPRINGER SE RIES IN PHOTONICS 3

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SPRINGER SERIES IN PHOTONICS

The Springer Series in Photonics covers the entire field of photonics, including theory, experiment, and the technology of photonic devices. The books published in this series give a careful survey of the state-of-the-art in photonic science and technology for all the relevant classes of active and passive photonic components and materials. This series will appeal to researchers, engineers, and advanced students.

Advanced Optoelectronic Devices By D. Dragoman and M. Dragoman

2 Femtosecond Technology Editors: T. Kamiya, F. Saito, O. Wada, H. Yajima

3 Integrated Silicon Optoelectronics By H. Zimmermann

Horst Zimmermann

Integrated Silicon Optoelectron ics

With 257 Figures and 18 Tables

, Springer

Dr.-Ing. habil. Horst Zimmermann, Dipl.Phys. Christian-Albrechts-Universität, Technische Fakultät, Halbleitertechnik Kaiserstrasse 2, 24143 Kiel, Germany E-Mail: horst. zimmermann(Qieee . org

Series Editors: Professor Takeshi Kamiya Department of Electronic Engineering, Faculty of Engineering University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

Professor Bo Monemar Department ofPhysics and Measurement Technology, Materials Science Division Linköping University 58183 Linköping, Sweden

Dr. Herbert Venghaus Heinrich-Hertz-Institut für Nachrichtentechnik Berlin GmbH Einsteinufer 37 10587 Berlin, Germany

Library ofCongress Cataloging-in-Publication Data

Zimmermann, Horst, 1957-Integrated silicon optoelectronics / Horst Zimmermann.

p. cm. -- (Springer series in photonics ; 3) Inc1udes bibliographical references and index. 1. Optoelectronic devices. 2. Integrated circuits. 3. Semiconductors. 4.

Silicon-on-insulator technology. I. Tide. 11. Springer series in photonics ; v. 3.

TK8304 .Z56 2000 621.381'045--dc21

ISSN 1437-0379

ISBN 978-3-662-04020-1 ISBN 978-3-662-04018-8 (eBook) DOI 10.1007/978-3-662-04018-8

99-088579

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© Springer-Verlag Berlin Heidelberg 2000 Originally published by Springer-Verlag Berlin Heidelberg New York in 2000. Softcover reprint ofthe hardcover 1st edition 2000

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Preface

This book is intended as a bridge between microelectronics and optoelec­tronics. Usually, optoelectronics plays a minor role in electrical engineering courses at universities. Physicists are taught optics but not very much semi­conductor technology and chip design. This book covers the missing informa­tion for engineers and physicists who want to know more about integrated optoelectronic circuits (üElCs) in silicon technologies and about their emerg­ing possibilities.

üptoelectronics usually implies that IIljV semiconductor materials are involved. This is the case when ultra-high-speed photodetectors or efficient light emitters are needed. For other applications, the price of IIljV photode­tectors and üElCs is simply too high. Silicon photodectectors and receiver üElCs, therefore, are the only choice when high volumes are needed and the price has to be low as, for instance, in consumer electronics. Such high volumes of silicon üElCs are, for example, needed in optical storage sys­tems like audio CD, magneto-optical disk, CD-RüM, and Digital-Video-Disk or Digital-Versatile-Disk (DVD) systems. The market for DVD systems and therefore for DVD üElCs is estimated to be 120 million pieces in the year 2001.

üElCs are key devices for advanced üptical storage systems and für the enhancement of their speed and data rate. This importance of üElCs is due to the following advantages of monolithic optoelectronic integrated circuits: (i) good immunity against electromagnetic interference (EMl) because of very short interconnects between photodetectors and amplifiers, (ii) reduced chip area due to the elimination of bondpads, (iii) improved reliability due to the elimination of bondpads and bond wires, (iv) cheaper mass production compared to discrete circuits, wire-bonded circuits, and hybrid integrated circuits, and (v) larger -3dB bandwidth compared to discrete circuits, wire­bonded circuits, and some hybrid integrated circuits due to the avoidance of parasitic bondpad capacitances.

Even in the domain of light emission, silicon is being investigated inten­sively to make silicon a competitor of lIIjV semiconductor materials. Much effort is made to let silicon emit light, and these attempts will be described in this book.

VI Preface

This book was written in parallel with the development of OEICs in CMOS and in BiCMOS technologies for optical storage systems andfor opti­cal interconnect technologies. It describes the state of the art in OEIC design and the approaches to this topic reported recently in the literature.

Parts of the book have their origin in an 'Optoelectronies' lecture I have given since 1994. It, however, dives much deeper into the topic. The possi­bilities of integrated silicon optoelectronies are investigated thoroughly and I have tried to initiate a link between mieroelectronies and photonics. The term photonies has come into use more and more in the last decade. This term, whieh was coined in analogy with electronies, reflects the growing link between opties and electronies forged by the increasing role of semiconductor materials and deviees in optieal systems.

As the term electronics already expresses, it is based on the control of electrons and of electrie charge flow. Photonics is based on the control of photons, and the term photonies reflects the importance of the photon nature of light in describing the operation of many optical deviees. The overlap between the two disciplines is obvious, since electrons often control the flow of photons and, conversely, photons control the flow of electrons. The term photonies is used broadly to encompass: (i) the generation of light by LEDs and lasers; (ii) the transmission of light in free space, through conventional optieallenses, apertures, and imaging systems, and through optieal fibers and waveguides; (iii) the modulation, switching, and scanning of light by the use of electrieally, acoustieally, or optieally controlled deviees; (iv) the amplification and frequency conversion of light by the use of wave interaction in nonlinear materials; (v) the detection of light.

These areas have found steadily increasing applications in optical commu­nication, signal processing, computing, sensing, display technology, printing, and energy transport. Items (i) to (iii) and (v) can be covered by silicon and will be discussed in this book.

Integrated optoelectronie receiver circuits have already made their way into mieroelectronics, whieh is dominated by silicon technology. I think it is only a question of time before true mierophotonie silicon-based circuits with electronie circuits, light detectors, waveguides, grating couplers, holographie lenses, and efficient light emitters are developed and enter the market.

I would like to thank Prof. Dr.-Ing. P. Seegebrecht for the generous pos­sibility to develop OEICs independently and for several helpful comments concerning apart of the text used to acquire the title 'habilitatus'. I am also indebted to Prof. Dr. H. Föll, who offered a waferprober for the charac­terization of the OEICs. The work of the OEIC group members, A. Ghazi, T. Heide, K. KiE;lschniek, and G. Volkholz, is highly appreciated. Three stu­dents, N. Madeja, F. Sievers, and U. Willecke, carefully performed simulations and measurements. M. Wieseke and F. Wölk helped with the preparation of numerous drawings. Special thanks go to R. Buchner from the Fraunhofer­Institute for Solid-State Technology in Munieh and H. Pless from Thesys

Preface VII

Microelectronics in Erfurt for their engagement in the fabrication of CMOS OElCs and BiCMOS OElCs, respectively. Last but not least I would like to gratefully acknowledge the funding of the projects by the German ministry for education, science, research, and technology (BMBF) within the leading project 'optical memories' .

I extend my sincere thanks to Dr. Ascheron and his team at Springer for the good cooperation and their technical support with the text processor. My deepest gratitude, however, is directed to my wife and my daugthers, Luise and Lina, who supported this book project with their encouragement and patience during many evenings and weekends.

Kiel, January 2000 Horst Zimmermann

Contents

List of Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. XIII

1. Basics of Optical Emission and Absorption.. .... ... ... ... 1 1.1 Properties of Light ..................................... 1 1.2 Energy Bands of Semiconductor Materials. . . . . . . . . . . . . . . . . 2 1.3 Optical Absorption of Semiconductor Materials ............ 4 1.4 Photogeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.5 External Quantum Efficiency and Responsivity . . . . . . . . . . . . . 7

2. Theory................................................... 11 2.1 Semiconductor Equations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11 2.2 Important Models for Photodetectors ... . . . . . . . . . . . . . . . . .. 15

2.2.1 Carrier Drift. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15 2.2.2 Carrier Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 19 2.2.3 Internal Quantum Efficiency . . . . . . . . . . . . . . . . . . . . . .. 22 2.2.4 Equivalent Circuit of a Photodiode. . . . . . . . . . . . . . . .. 24

3. Silicon Technologies and Integrated Photodetectors . . . . . .. 29 3.1 Bipolar Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 29 3.2 Integrated Detectors in Standard Bipolar Technology ....... 32

3.2.1 Photodiodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 32 3.2.2 Phototransistors ................................. 34

3.3 Integrated Detectors in Modified Bipolar Technology . . . . . . .. 35 3.3.1 UV Sensor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 35 3.3.2 PIN Photodiode Integration ....................... 36 3.3.3 Color Sensor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 39

3.4 CMOS Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 41 3.4.1 One-WeH Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 41 3.4.2 . Twin-WeH Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 41

3.5 CMOS-Integrated Detectors ............................. 43 3.5.1 Integrated Detectors in Standard CMOS Processes ... 43 3.5.2 PIN Photodiode Integration. . . . . . . . . . . . . . . . . . . . . .. 48 3.5.3 Finger Photodiodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 7I 3.5.4 Particle Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 75

X Contents

3.5.5 Charge-Coupled-Device Image Sensors. . . . . . . . . . . . .. 76 3.5.6 Active-Pixel Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 81 3.5.7 Schottky Photodiodes . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 86 3.5.8 MSM-Photodetectors............................. 95 3.5.9 Amorphous-Silicon Detectors ...................... 99 3.5.10 Bipolar Phototransistors .......................... 105 3.5.11 Field-Effect Phototransistors ....................... 109

3.6 BiCMOS Processes ..................................... 113 3.7 BiCMOS-Integrated Detectors ........................... 119

4. Optoelectronic Devices in Silicon-on-Insulator ............ 129 4.1 Photodiodes in SOl ..................................... 129 4.2 Phototransistors in sor ................................. 136 4.3 Optical Modulators in sor .............................. 137

5. Silicon Power Devices .................................... 139 5.1 Light-Activated Thyristors ............................... 139 5.2 Light-Activated Triac ................................... 142

6. SiGe Photodetectors ...................................... 145 6.1 Heteroepitaxial Growth ................................. 145 6.2 Absorption Coefficient of SiGe Alloys ..................... 146 6.3 SiGe IR Photodetector .................................. 147 6.4 SiGeC ................................................ 149 6.5 SiGe Waveguide Photodetector ........................... 150 6.6 Long-Wavelength Infrared SiGe Photoconductor ............ 153 6.7 SiGejSi PIN Hetero-Bipolar-Transistor Integration ......... 157

7. Detectors Based on aResonant Cavity ................... 161 7.1 .Principle of Resonant Cavity Enhanced Detectors .......... 161 7.2 Example of aResonant Cavity Enhanced Silicon Detector ... 164

8. 111-V Semiconductor Materials on Silicon ................. 167 8.1 Heteroepitaxial Growth ................................. 167 8.2 Flip-chip Hybridization Technique ........................ 173 8.3 Wafer Bonding ......................................... 179

8.3.1 Wafer Bonded Photodetectors ...................... 181 8.3.2 Wafer Bonded Light Emitters ...................... 182

9. Silicon Light Emitters .................................... 187 9.1 Quantum-Size Silicon ................................... 187 9.2 SiGe and SiGeC ........................................ 193 9.3 Erbium-Doped Silicon ................................... 194

Contents XI

9.4 Semiconducting Silicides ................................. 197 9.5 Organic Polymers on Silicon ............................. 198 9.6 Liquid Crystals ........................................ 199

10. Integrated Optics ......................................... 203 10.1 Waveguides ............................................ 203

10.1.1 Total Reflection .................................. 203 10.1.2 Losses .......................................... 204 10.1.3 Waveguides for Visible and lnfrared Light ........... 204 10.1.4 Waveguides for lnfrared Light ...................... 209

10.2 Photonic Bandgap Filter ................................ 212 10.3 Optical Amplifier ....................................... 215 10.4 Examples of lntegrated Optical Systems ................... 217

10.4.1 Optical lnterconnects ............................. 217 10.4.2 Optical Transceiver ............................... 221 10.4.3 Micro-Spectrometer ............................... 222 10.4.4 Optical Pressure Sensor ........................... 224 10.4.5 Optical Distance Sensor ........................... 225 10.4.6 Optical Pickup Devices ........................... 225

11. Design of Integrated Circuits ............................. 229 11.1 Circuit Simulators and Transistor Models .................. 229 11.2 Layout and Verification Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 11.3 Design of OElCs ....................................... 235 11.4 Transimpedance Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

12. Examples of Optoelectronic Integrated Circuits ........... 249 12.1 Digital CMOS Circuits .................................. 249

12.1.1 Synchronous Circuits ............................. 249 12.1.2 Asynchronous Circuits ... ' ......................... 253

12.2 Digital BiCMOS Circuits ................................ 255 12.3 Laser Driver Circuits .................................... 256 12.4 Analog Circuits ........................................ 259

12.4.1 Bipolar Circuits .................................. 259 12.4.2 CMOS lmagers .................................. 262 12.4.3 CMOS Circuits for Optical Storage Systems ......... 266 12.4.4 BiCMOS Circuits for Optical Storage Systems ....... 272 12.4.5 Fiber Receivers .................................. 280

12.5 Summary .............................................. 294

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

Index ......................................................... 325

List of Symbols

Symbol Description Unit

a Lattice constant nm A Area cm2

Ao Low-frequency open loop gain A(w) Frequency-dependent gain C Speed of light in a medium cmjs Co Speed of light in vacuum cmjs Cbd SmaIl-signal bulk-drain capacitance F Cbs Small-signal bulk-source capacitance F Ces SmaIl-signal collector-substrate capacitance F Cgb SmaIl-signal gate-bulk capacitance F Cgd SmaIl-signal gate-drain capacitance F Cgs SmaIl-signal gate-source capacitance F Cws Small-signal weIl-substrate capacitance F Cje SmaIl-signal emitter-base capacitance F cJl. SmaIl-signal base-collector capacitance F Ce Doping concentration of epitaxial layer cm-3

CB Capacitance of bondpad F CBE Base-emitter capacitance F Ce Base-collector space-charge capacitance F CD Depletion capacitance of photodiode F CE Total base-emitter capacitance of bipolar transistor F CF Feedback capacitance of transimpedance amplifier F CI Input capacitance of amplifier F CL Load capacitor F Cp Capacitance of chip package F CRF Parasitic capacitance of feedback resistor F Cs Parasitic capacitance of signal line F CSE Base-emitter space-charge capacitance F

XIV List of Symbols

Symbol Description Unit

de Thickness of epitaxiallayer lJ.Ill dI Thickness of intrinsic region lJ.Ill dp Thickness of P-type region lJ.Ill D Diffusion coefficient cm2/s Dn Diffusion coefficient of electrons cm2/s Dp Diffusion coefficient of holes cm2/s DR Data rate Mb/s Ee Bottom of conduction band eV EF Fermi energy level eV Eg Energy bandgap eV Ep Phonon energy eV E t Energy level of recombination center eV Ev Top of valence band eV E Photon energy eV E Electric field V/cm f Frequency Hz fg Bandwidth, -3dB frequency Hz

h Transit frequency (gain-bandwidth product) Hz fap Frequency of gain-peak Hz G Photogeneration (e-h-p) cm-3 /s G(w) Frequency response function VIA 9m Transconductance A/V h Planck constant Js fi h/27f Js hv Photon energy eV I Current A 1ph Photocurrent A 1t h Threshold current A 1B Base current A 1e Collector current A 1D Drain current A 1E Emitter current A 18 Source current A j Current density A/cm2

k Wave vector cm-1

kB Boltzmann constant J/K kBT Thermal energy eV L Length lJ.Ill

Ln Diffusion length of electrons ~m

List of Symbols xv

Symbol Description Unit

Lp Diffusion length of holes Jllll L B Inductance of bond wire H L G Gate length Jllll Lw Inductance of lead wire H Ti Refractive index Tis Refractive index of surroundings Tisc Refractive index of semiconductor TiARC Refractive index of antireflection coating n Density of free electrons cm-3

ni Intrinsic density cm-3

N Impurity concentration cm-3

NA Acceptor concentration cm-3

N n Donor concentration cm-3

Nt Concentration of recombination centers cm-3

p Density of free holes cm-3

QE Minority-carrier charge in the base As Qpix Charge on pixel storage capacitor As QE Quantum efliciency % p Momentum Js/m Popt Incident optical power W P Optical power in a semiconductor W q Magnitude of electronic charge As Tb Base series resistance n To Small-signal output resistance n Tc Small-signal collector series resistance n Tex Small-signal emitter series resistance n Td Small-signal drain series resistance n Ts Small-signal source series resistance n R Responsivity A/W Rbb Responsivity to black-body radiation A/W Rn Parallel resistance n RF Feedback resistance n Rs Series resistance n RI Input resistance of amplifier n RL Load resistance n R Reflectivity t Time s td Drift time s tdiff Diffusion time s tf Fall time s

XVI List of Symbols

Symbol Description Unit

t r Rise time s tgd Group delay s T Absolute temperature K U Voltage V UBE Base-emitter voltage V UD BuHt-in voltage V UDS Drain-source voltage V UEa Early voltage V UGS Gate-source voltage V UT Thermal voltage kB T / q V Uth Thermal generation/recombination rate cm-3s- 1

UTh Threshold voltage V Vdet Detector bias V Vo Output voltage V Vrev Reverse voltage V v Carrier velo city cm/s V s Saturation velocity cm/s Vth Thermal velocity cm/s W Width of space-charge region lJ.IIl WB Base thickness lJ.IIl WG Gate width lJ.IIl ZF Feedback impedance of transimpedance amplifier n x x direction lJ.IIl y Y direction lJ.IIl Q Absorption coefficient 1J.IIl-1

ß Current gain of bipolar transistor 1]e External (total) quantum efficiency % 1]i Internal quantum efficiency % 1]0 Optical quantum efficiency % 1]mc Emission enhancement factor in micro-cavity 100 Permittivity in vacuum F/cm IOd Relative permittivity of passivation layer f r Relative permittivity lOs Semiconductor permittivity F/cm E Dielectric function er Carrier capture cross seetion cm-2

T Lifetime s Tn Electron lifetime s Tp Hole lifetime s TB Base transit time s

List of Symbols XVII

Symbol Description Unit

K, Extinction coefficient A Wavelength in a medium nm AO Wavelength in vacuum nm Ac Wavelength corresponding to Eg nm Ad Design wavelength of a DBR nm Ach Channel length modulation parameter V-I

v Frequency of light Hz

J.L Mobility cm2 jVs J.Ln Electron mobility cm2 jVs J.Lp Hole mobility cm2 jVs W Angular frequency s-1

WT 2"7l"'fT s-1

WGP 2"7l"'fGP s-1

p Charge density Asjcm3

qJ Photon flux density cm-2s-1

qJB Barrier height eV qJbi BuHt-in potential V i[t Potential V B Angle 0

Bc Critical angle for total reflection 0

Bi Incidence angle 0