UNIVERSITY OF CALIFORNIA Santa Barbara Travelling-Wave Photodetectors by Kirk Steven Giboney A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering Committee in Charge Professor John E. Bowers, Co-Chairperson Professor Mark J. W. Rodwell, Co-Chairperson Professor Larry A. Coldren Professor Umesh K. Mishra August 1995 The dissertation of Kirk Steven Giboney is approved August 1995 ii August 4, 1995 Travelling-Wave Photodetectors Copyright © 1995 by Kirk Steven Giboney iii ACKNOWLEDGEMENTS – Beauty makes our pursuits worthwhile. – Progress flows only from collective efforts. Individuals can claim no more than incremental contributions. Even so, the aptly exploited talents are not earned, but merely developed. Like our talents, our associations with our contemporaries are gifts that we choose to develop. I would like to thank several people who contributed to my education and this work. A thesis advisor is a lot like a parent for the graduate student's intellectual and professional development. My advisors, Mark Rodwell and John Bowers, took their roles as seriously. Their technical guidance, support, and impetus, enabled this work, and greatly enhanced my life. My committee, which also included Larry Coldren and Umesh Mishra, made whole-hearted efforts not only to direct outstanding research, but to communicate the personal and professional aspects crucial to success. The faculty have set an invaluable example of cooperation and collaboration that has been enthusiastically embraced throughout the department by staff, graduate students, and visiting and postdoctoral researchers. Radha Nagarajan helped me develop the process I used. Tom Reynolds balanced a difficult job of keeping the labs running while making significant contributions to individual research, such as the anti-reflection coatings on the travelling-wave photodetectors. Rich Mirin made sure the material he grew was appropriate and done right the first time. I learned much about high-speed photodetectors from Yih-Guei Wey while doing electro-optic sampling measurements on his. Daily interactions among researchers contribute substantially to research results, professional maturity, and personal satisfaction. Many fruits of my interactions with Scott Allen and Masayuki Kamegawa, particularly related to device processing, were incorporated into this work. Judy Karin helped me get started on the optical bench. Dan Tauber, Ralph Spickerman, and Mike Case were comrades in microwave devices and slow-wave effects, and together, we planted many seeds of ideas. Dennis Derickson showed me the detailed workings of mode-locked semiconductor lasers. I worked with Mark Mondry at McDonnell Douglas before we came to UCSB, and we engaged in many discussions on a wide range of subjects at both places. Anish Goyal iv and Dubravko Babic were always willing to discuss anything and offer help. Dan Cohen supported Professor Coldren's group and managed to help others while working on his thesis. It has been a pleasure to work alongside many others. In Professor Bowers' group were Roger Helkey, Wenbin Jiang, Gary Wang, Chi-Kuang Sun, Rajeev Ram, Jim Dudley, Alan Mar, Pat Corvini, John Wasserbauer, Debbie Crawford, Paul Morton, Peter Blixt, Anders Petersen, Aaron Hawkins, and Kehl Sink. In Professor Rodwell's group were Ruai Yu, Eric Carman, Kimi Abe, Yoshiyuki Konishi, Uddalak Bhattacharya, Madhukar Reddy, Bipul Agarwal, Rajasekhar Pullela, and James Guthrie. There were also Scott Campbell, Joyce Olsen, Jong Chang Yi, Chi-Ping Chao, Eva Strzelecka, and many others. My special appreciation goes to Lorene Inouye for helping me to keep in balance. I cherish our friendships and experiences together far above any other aspect of my time at UCSB. I am happy that you all shared your time and efforts with me. I thank ARPA Optoelectronics Technology Center and Ultra Program administered by Anis Husain and Robert Leheny, Charles Tsacoyeanes at Rome Laboratories, Joe Weller at the ONT Block Program on Electro-Optics Technology, and the United States Congress for their support. I am grateful to the American taxpayers for providing funding for this work, and to the California taxpayers for funding the University of California. I especially appreciate my parents and grandmother, and my brother and sister and their families for their support and love, and for helping me to keep my values straight. v VITA July 19, 1960 Born, Bakersfield, California, USA December 1984 B.S. Physics, University of California, Davis August 1985 – August 1988 Senior Engineer, McDonnell Douglas Astronautics Company, Huntington Beach, California December 1990 M.S. Electrical and Computer Engineering, University of California, Santa Barbara April 1989 – July 1995 Graduate Student Researcher, University of California, Santa Barbara July 1990 – July 1995 Technical Consultant, Hughes Research Laboratories, Malibu, California July 1995 – Research Intern VI, Hewlett-Packard Laboratories, Palo Alto, California Publications 34. Yih-Guei Wey, Kirk Giboney, John Bowers, Mark Rodwell, Pierre Silvestre, Prabhu Thiagarajan, and Gary Robinson, "110 GHz GaInAs/InP Double Heterostructure p-i-n Photodetectors," J. Lightwave Technol., vol. 13, no. 7, pp. 1490-1499, Jul., 1995. 33. Kirk Giboney, John Bowers, and Mark Rodwell, "Travelling-Wave Photodetectors," in 1995 IEEE MTT-S Microwave Symposium Digest, pp. 159-162, May 15-19, 1995. (Invited) 32. Kirk S. Giboney, Mark J. W. Rodwell, and John E. Bowers, "Field-Screening Effects in Travelling-Wave and Vertically Illuminated p-i-n Photodetectors," presented at 1995 Conf. Lasers Electro-Optics, Baltimore, MD, May, 1995, CFB4. 31. Kirk S. Giboney, Radhakrishnan L. Nagarajan, Thomas E. Reynolds, Scott T. Allen, Richard P. Mirin, Mark J. W. Rodwell, and John E. Bowers, "Travelling-Wave Photodetectors with 172 GHz Bandwidth and 76 GHz Bandwidth-Efficiency Product," IEEE Photon. Technol. Lett., vol. 7, no. 4, pp. 412-414, Apr., 1995. 30. Kirk S. Giboney, Scott T. Allen, Mark J. W. Rodwell, and John E. Bowers, "Picosecond Measurements by Free-Running Electro-Optic Sampling," IEEE Photon. Technol. Lett., vol. 6, no. 11, pp. 1353-1355, Nov., 1994. 29. Radhakrishnan Nagarajan, Kirk Giboney, Rangchen Yu, Daniel Tauber, John Bowers, and Mark Rodwell, "High-Speed Optoelectronics," presented at 21st Int. Symp. Compound Semicond., San Diego, CA, Sep., 1994, WP3.1. (Invited) vi 28. R. H. Walden, W. E. Stanchina, R. A. Metzger, R. Y. Loo, J. Schaffner, M. W. Pierce, Y. K. Brown, F. Williams, V. Jones, J. Pikulski, M. Rodwell, K. Giboney, R. A. Mullen, R. WongQuen, and J. F. Jensen, "InP-Based Optoelectronic Integrated Receiver Front-Ends Using Heterojunction Bipolar Transistors and Base-Collector Photodiodes," presented at Eng. Found. Third Conf. High Speed Optoelectron. Devices for Commun. and Interconnects, Shell Beach, CA, Aug., 1994. (Invited) 27. Kirk Giboney, Mark Rodwell, and John Bowers, "Travelling-Wave Photodetectors," presented at Eng. Found. Third Conf. High Speed Optoelectron. Devices for Commun. and Interconnects, Shell Beach, CA, Aug., 1994. (Invited) 26. Kirk Giboney, Radhakrishnan Nagarajan, Thomas Reynolds, Scott Allen, Richard Mirin, Mark Rodwell, and John Bowers, "172 GHz, 42% Quantum Efficiency p-i-n Travelling- Wave Photodetector," presented at 52nd Annual Device Res. Conf., Boulder, CO, Jun., 1994, VIA-9. 25. Kirk S. Giboney, Scott T. Allen, Mark J. W. Rodwell, and John E. Bowers, "1.5 ps Fall- Time Measurements by Free-Running Electro-Optic Sampling," presented at Conf. Lasers Electro-Optics, Anaheim, CA, May, 1994, CME4. 24. R. H. Walden, W. E. Stanchina, R. A. Metzger, R. Y. Loo, J. Schaffner, M. W. Pierce, Y. K. Brown, F. Williams, V. Jones, J. Pikulski, M. Rodwell, K. Giboney, R. A. Mullen, and J. F. Jensen, "Broadband optoelectronic integrated receiver front-ends comprising InP- based heterojunction bipolar transistors and base-collector photodiodes," presented at Conf. Optical Fiber Commun., San Jose, CA, Feb., 1994. 23. Yih-Guei Wey, Kirk S. Giboney, John E. Bowers, Mark J. W. Rodwell, Pierre Silvestre, Prabhu Thiagarajan, and Gary Y. Robinson, "108 GHz GaInAs/InP p–i–n Photodiodes with Integrated Bias Tees and Matched Resistors," IEEE Photon. Technol. Lett., vol. 5, no. 11, pp. 1310-1312, Nov., 1993. 22. John Bowers, Kirk Giboney, Yih-Guei Wey, Mark Rodwell, "New Concepts in 100 GHz High-Efficiency Photodetectors," presented at LEOS Summer Topical Meeting Optical Microwave Interactions, Santa Barbara, Jul., 1993, M1.1. (Invited) 21. Kirk S. Giboney, Yih-Guei Wey, John E. Bowers, Mark J. W. Rodwell, Pierre Silvestre, Prabhu Thiagarajan, and Gary Y. Robinson, "High-Speed GaInAs/InP p-i-n Photodiodes with Integrated Bias Tees," presented at Fifth Int. Conf. Indium Phosphide and Related Mater., Paris, France, Apr., 1993, TuE5. 20. Yih-Guei Wey, Kirk S. Giboney, John E. Bowers, Mark J. W. Rodwell, Pierre Silvestre, Prabhu Thiagarajan, and Gary Y. Robinson, "110 GHz Double Heterostructure GaInAs/InP p-i-n Photodiode," in OSA Proc. Ultrafast Electron. Optoelectron., vol. 14, pp. 45-48, 1993. 19. Kirk S. Giboney, Mark J. W. Rodwell, and John E. Bowers, "Traveling-Wave Photodetectors," IEEE Photon. Technol. Lett., vol. 4, no. 12, pp. 1363-1365, Dec., 1992. vii 18. J. G. Wasserbauer, D. J. Derickson, K. Giboney, R. J. Helkey, J. R. Karin, A. Mar, and J. E. Bowers, "Integrated Optical Transmitters and Receivers Using Multi-Segment Laser Processes," presented at LEOS Summer Topical Meeting Optical Microwave Interactions, Santa Barbara, Jul., 1992. 17. Eric Carman, Michael Case, Masayuki Kamegawa, Ruai Yu, Kirk Giboney, and M. J. W. Rodwell, "V-Band and W-Band Broad-Band, Monolithic Distributed Frequency Multipliers," IEEE Microwave Guided Wave Lett., vol. 2, no. 6, pp. 253-254, Jun., 1992. 16. Eric Carman, Michael Case, Masayuki Kamegawa, Ruai Yu, Kirk Giboney, and M. J. W. Rodwell, "V-Band and W-Band Broad-Band, Monolithic Distributed Frequency Multipliers," presented at 1992 IEEE MTT-S Int. Microwave Symp., Albuquerque, NM, Jun., 1992 (in 1992 IEEE MTT-S Microwave Symposium Digest, pp. 819-22, Jun. 1-5, 1992). 15. Eric Carman, Michael Case, Masayuki Kamegawa, Ruai Yu, Kirk Giboney, and M. J. W. Rodwell, "Electrical Soliton Devices as >100 GHz Signal Sources," presented at Ultrafast Phenomena VIII Conf., Antibes, France, Jun., 1992. 14. M. J. W. Rodwell, Scott Allen, Masayuki Kamegawa, Kirk Giboney, Judy Karin, Michael Case, Ruai Y. Yu, and J. E. Bowers, "Picosecond Photodetectors Monolithically Integrated with High-Speed Sampling Circuits," presented at AFCEA DOD Fiber Opt. Conf., Mar., 1992. 13. Mark J. W. Rodwell, Masayuki Kamegawa, Ruai Yu, Michael Case, Eric Carman, and Kirk S. Giboney, "GaAs Nonlinear Transmission Lines for Picosecond Pulse Generation and Millimeter-Wave Sampling," IEEE Trans. Microwave Theory Tech., vol. 39, no. 7, pp. 1194-1204, Jul., 1991. 12. M. Kamegawa, K. Giboney, J. Karin, S. Allen, M. Case, R. Yu, M. J. W. Rodwell, and J. E. Bowers, "Picosecond GaAs Monolithic Optoelectronic Sampling Circuit," IEEE Photon. Technol. Lett., vol. 3, no. 6, pp. 567-569, Jun., 1991. 11. Y. G. Wey, D. L. Crawford, K. Giboney, J. E. Bowers, M. J. Rodwell, P. M. Sylvestre, M. J. Hafich, and G. Y. Robinson, "Ultrafast graded double-heterostructure GaInAs/InP photodiode," Appl. Phys. Lett., vol. 58, no. 19, pp. 2156-2158, May 13, 1991. 10. M. J. W. Rodwell, Masayuki Kamegawa, Michael Case, Ruai Y. Yu, and Kirk Giboney, Eric Carman, Judy Karin, Scott Allen, and Jeff Franklin, "Nonlinear Transmission Lines and their Applications in Picosecond Optoelectronic and Electronic Measurements," presented at Eng. Found. Conf. High Freq./High Speed Optoelectron., Palm Beach, FL, Mar., 1991. 9. Y. Wey, D. Crawford, K. Giboney, A. Mar, J. Bowers, "Graded Double Heterostructure Photodetectors," presented at Eng. Found. Conf. High Freq./High Speed Optoelectron., Palm Beach, FL, Mar., 1991. 8. D. L. Crawford, Y. G. Wey, K. Giboney, M. Rodwell, J. Bowers, P. Sylvestre, M. Hafich, and G. Robinson, "3.8 ps FWHM Impulse Response of a Graded Double Heterostructure P- I-N Photodiode Fabricated on a Semi-Insulating Substrate," presented at Third Int. Conf. Indium Phosphide and Related Mater., Cardiff, Wales, 1991. viii 7. D. L. Crawford, Y. G. Wey, J. E. Bowers, K. Giboney, and M. Rodwell, "New Directions in High Speed Photodetectors," presented at Conf. Lasers Electro-Optics, Baltimore, MD, 1991, CWB6. (Invited) 6. Michael Case, Eric Carman, Masayuki Kamegawa, Kirk Giboney, Ruai Yu, Kathryn Abe, M. J. W. Rodwell, and Jeff Franklin, "Impulse Generation and Frequency Multiplication Using Soliton Effects in Monolithic GaAs Circuits," in OSA Proc. Picosecond Electron. Optoelectron., vol. 9, pp. 140-144, 1991. 5. Masayuki Kamegawa, K. Giboney, J. Karin, S. Allen, M. Case, R. Yu, M. J. W. Rodwell, and J. E. Bowers, "Picosecond GaAs Photodetector Monolithically Integrated with a High- Speed Sampling Circuit," in OSA Proc. Picosecond Electron. Optoelectron., vol. 9, pp. 104-107, 1991. 4. D. L. Crawford, Y. G. Wey, K. Giboney, J. E. Bowers, M. J. Rodwell, P. M. Sylvestre, M. J. Hafich, and G. Y. Robinson, "Ultrafast Graded Double-Heterostructure p-i-n Photodiode," in OSA Proc. Picosecond Electron. Optoelectron., vol. 9, pp. 92-96, 1991. (Invited) 3. Eric Carman, Kirk Giboney, Michael Case, Masayuki Kamegawa, Ruai Yu, Kathryn Abe, M. J. W. Rodwell, and Jeff Franklin, "28–39 GHz Distributed Harmonic Generation on a Soliton Nonlinear Transmission Line," IEEE Microwave Guided Wave Lett., vol. 1, no. 2, pp. 28-31, Feb., 1991. 2. Y. G. Wey, M. Kamegawa, A. Mar, K. J. Williams, K. Giboney, D. L. Crawford, J. E. Bowers, and M. Rodwell, "Hybrid Integration of an InGaAs/InP PIN Photodiode with an Ultrafast Sampling Circuit," presented at Conf. Optical Fiber Commun., San Diego, CA, 1991, PD8-1. 1. M. Case, M. Kamegawa, K. Giboney, M. Rodwell, J. Franklin, and J. E. Bowers, "62.5 ps to 5.5 ps Soliton Compression on a Monolithic Nonlinear Transmission Line," presented at 48th Annual Device Res. Conf., Santa Barbara, CA, Jun., 1990, VA-2. ix ABSTRACT Travelling-Wave Photodetectors by Kirk Steven Giboney Photodetector efficiency decreases as bandwidth increases. Bandwidth-efficiency products of vertically illuminated photodetectors are limited to about 40 GHz. This product imposes a bound on the speed and sensitivity of photoreceivers used in optical transmission systems. Waveguide photodetectors are an attractive option for increasing the bandwidth- efficiency product over the intrinsic limit of vertically illuminated photodetectors. By guiding the illumination perpendicular to the carrier drift field, the inherent tradeoff between efficiency and the transit-time bandwidth limitation is diminished. However, even higher bandwidth-efficiency products are possible with consideration for the propagation of the electrical waves to the load. Attention to the microwave design of waveguide photodetectors leads to travelling-wave photodetectors. A travelling-wave photodetector is a waveguide photodetector with an electrode structure designed to support travelling electrical waves with characteristic impedance matched to that of the external circuit. The travelling-wave photodetector is thus modelled by a matched section of transmission line with an exponentially decaying photocurrent source propagating on it at the optical group velocity. The mismatch between the group velocity of the photocurrent source and the phase velocities of the electrical waves it generates limits travelling-wave photodetector bandwidth. The velocity-mismatch bandwidth limitation is essentially independent of device length, so a travelling-wave photodetector can arbitrarily be made long enough for nearly 100% internal quantum efficiency without compromising bandwidth. A simple form for the velocity-mismatch bandwidth limitation is derived that affords physical insight and provides a basis for using traditional design methods. The first theory, fabrication, and measurement of travelling-wave photodetectors comprise this thesis work. New developments in electro-optic techniques enable measurements of bandwidths as high as 190 GHz, the highest reported for a p-i-n photodetector by more than 70%. The travelling-wave photodetectors display bandwidth-efficiency products as large as 84 GHz, breaking the record for any photodetector without gain by 50%. Comparisons with vertically illuminated and waveguide photodetectors fabricated on the same wafer establish the advantage of travelling-wave photodetectors. x