III-nitride Photonic Integrated Circuit: Multi-section GaN Laser Diodes for Smart Lighting and Visible Light Communication Dissertation by Chao Shen In Partial Fulfillment of the Requirements For the Degree of Doctor of Philosophy King Abdullah University of Science and Technology Thuwal, Kingdom of Saudi Arabia April, 2017 2 EXAMINATION COMMITTEE PAGE The dissertation of Chao Shen is approved by the examination committee. Committee Chairperson: Prof. Boon S. Ooi Committee Member: Prof. Kazuhiro Ohkawa, Prof. Lain-Jong Li, Prof. Jung Han (Yale University). COPYRIGHT PAGE 3 © April, 2017 Chao Shen All Rights Reserved 4 ABSTRACT III-nitride Photonic Integrated Circuit: Multi-section GaN Laser Diodes for Smart Lighting and Visible Light Communication Chao Shen The past decade witnessed the rapid development of III-nitride light-emitting diodes (LEDs) and laser diodes (LDs), for smart lighting, visible-light communication (VLC), optical storage, and internet-of-things. Recent studies suggested that the GaN-based LDs, which is free from efficiency droop, outperform LEDs as a viable high-power light source. Conventionally, the InGaN-based LDs are grown on polar, c-plane GaN substrates. However, a relatively low differential gain limited the device performance due to a significant polarization field in the active region. Therefore, the LDs grown on nonpolar m-plane and semipolar (2021)-plane GaN substrates are posed to deliver high-efficiency owing to the entirely or partially eliminated polarization field. To date, the smart lighting and VLC functionalities have been demonstrated based on discrete devices, such as LDs, transverse-transmission modulators, and waveguide photodetectors. The integration of III-nitride photonic components, including the light emitter, modulator, absorber, amplifier, and photodetector, towards the realization of III-nitride photonic integrated circuit (PIC) offers the advantages of small-footprint, high-speed, and low power consumption, which has yet to be investigated. This dissertation presents the design, fabrication, and characterization of the multi-section InGaN laser diodes with integrated 5 functionalities on semipolar (2021)-plane GaN substrates for enabling such photonic integration. The blue-emitting integrated waveguide modulator-laser diode (IWM-LD) exhibits a high modulation efficiency of 2.68 dB/V. A large extinction ratio of 11.3 dB is measured in the violet-emitting IWM-LD. Utilizing an integrated absorber, a high optical power (250mW), droop-free, speckle-free, and large modulation bandwidth (560MHz) blue-emitting superluminescent diode is reported. An integrated short-wavelength semiconductor optical amplifier with the laser diode at ~404 nm is demonstrated with a large gain of 5.32 dB at 6 V. A high-performance waveguide photodetector integrated LD at 405 nm sharing the single active region is presented, showing a significant large modulation bandwidth of 230 MHz. Thus these seamlessly integrated elements enable photonic IC at the visible wavelength for many important applications, such as smart lighting and display, optical communication, switching, clocking, and interconnect. The findings are therefore significant in developing an energy-saving platform technology that powers up human activities in a safe, health- and environmental-friendly manner. 6 ACKNOWLEDGEMENTS My sincere appreciation goes to my supervisor, Prof. Boon S. Ooi, a dedicated scientist, researcher, entrepreneur, leader, and badminton player, always with great passion and insights. His supervision and support helped me accomplish this dissertation research. I would also like to express my appreciation to our center manager, Dr. Tien Khee Ng, who is always helpful and accommodating. He spent so much time on discussing with me and has given numerous suggestions during my dissertation research. Besides, I would like to thank the great and lovely people I met at KAUST Photonics Laboratory: Dr. Zhao Chao, Dr. Liu Guangyu, and Dr. Mohd Sharizal Bin Alias provided continuous support and helped in my experiments. I learnt a lot from work done by MBE team, including Aditya Prabaswara, Bilal Janjua, Davide Priante, and Pawan Mishra. I enjoyed a lot when working closely with Hassan Oubei, Dr. It Ee Lee, Guo Yujian, Chen Rui, Zhang Zhenyu, and Sun Xiaobin on free-space and underwater optical communications. I would also thank Chun Hong Kang for the discussions related to GaN-based material processing. Very important, I highly appreciate the help and support from Ho Kang-Ting, Abeer AlSaggaf, Edgars Stegenburgs, Jorge Holguin Lerma, and Ram Chandra Subedi on device characterization and system testing. I would like to acknowledge many other lab mates and colleagues, such as Dr. AbdulMajid Mohammed, Dr. Mohammed Zahed Mustafa Khan, Dr. Damián San Román, Dr. Sakandar Rauf, Dr. Malleswararao Tangi, Dr. Mohamed Ebaid, Dr. Mohammad Khaled Shakfa, Dr. Rozalina Zakaria, Dr. Ahmed Ali AlJabr, Dr. Ahmed Ben Slimane, Dr. Hala Al-Hashim, Rami EiAfandy, Abdullah A. Alatawi, Abdullah A. Alhamoud, Liang Jian-Wei, Amanda Ooi, Liao Hsien-Yu, Aigerim Tankimanova, Zhang Huafan, Michele Conroy, and Yang Wenjian for sharing various experiences and making my days enjoyable and amusing. Special thanks to Ms. Khathijah Syed Osman, our center assistant, who provides highly efficient admin support to make the dissertation research goes smoothly. My appreciation also goes to my friends and colleagues and the department faculty and staff for making my time at KAUST a great experience. I would like to thank Prof. Osman Bakr, and his team members, including Mr. Ibrahim Dursun and Mr. Peng Wei, for the collaboration on the study of novel nanomaterials for optoelectronic applications. I would also like to thank Prof. Mohamed-Slim Alouini, Prof. He Jr-Hau, and Prof. Li Xiaohang, for the encouragement during my research. I have benefited from discussions with Dr. Ki- Hong Park on optical communications and Dr. Cheng Yingchun, especially his in-depth understanding of solid-state physics and experience in stimulating material properties in semiconductor materials. In addition, I would like to thank Dr. Sun Haiding, Dr. Jose Ramon Duran Retamal, Mr. Yang Shuai, Ms. Su Zhen, Mr. Farhan Abdul Ghaffar, Mr. Mahmoud Ouda, Mr. Li Ting-You, Mr. Lin Chun-Ho, Ms. Fu Hui-Chun, Mr. Wu Feng, Mr. Nasir Alfaraj, Mr. Li Kuang-Hui, Mr. Lin Ronghui in CEMSE division and Mr. Wang Zhenwei, Dr. Li Yangyang, Dr. Pan Jun in PSE division, who shared their research experience and provided useful information on equipment and lab operation. 7 Many of the experiments in my research would not be completed smoothly without the help from the scientists and engineers from KAUST’s core-laboratories. I would like to offer my great acknowledgement to Dr. Yang Yang for micro-Raman and PL measurements; Dr. Wang Xianbin, Dr. Wang Zhihong, and Mr. Basil Chew for lithography; Dr. Yue Weisheng, Mr. Li Jun, Mr. Wang Qingxiao, and Ms. Wei Nini for SEM imaging and FIB optimization; Dr. Chen Longqing and Dr. Max Chen for wet chemical process; Dr. Yao Yingbang and Mr. Kim Chong Wong for thermal annealing process; Mr. Ahad Syed for keeping ICP-RIE at very good condition; Dr. Li Liang for discussion of strain effect in semiconductors. I would express my great appreciations to the external collaborators at the University of California, Santa Barbara (UCSB) for growing the epitaxial structures and providing many help and support in the joint research project. Especially, the leading PIs of Solid State Lighting & Energy Electronics Center (SSLEEC), Prof. Shuji Nakamura, Prof. Steven P. DenBaars and Prof. James S. Speck, have been giving continuous support and encouragement during my dissertation research. I would also like to thank Dr. John T. Leonard and Mr. Changmin Lee for their help in preparing epitaxial materials and running some simulations. Besides, I also benefited from the discussions with Dr. Robert Farrell, Dr. Zhao Yuji, Dr. Erin Young, Dr. Arash Pourhashemi, and Dr. Anisa Myzaferi. I also want to extend my gratitude to the King Abdullah University of Science and Technology (KAUST) baseline funding, King Abdulaziz City for Science and Technology (KACST) Technology Innovation Center (TIC) for Solid State Lighting (KACST TIC R2-FP- 008), and the KACST-KAUST-UCSB Solid-State Lighting Program, which financially supports the research project. Finally, my heartfelt gratitude is extended to my family for their unconditional love and unweaving morale support. I would also thank many of my friends, who had enriched my life experience during my Ph.D. study. Shen Chao April, 2017 Thuwal, Kingdom of Saudi Arabia 8 TABLE OF CONTENTS Page EXAMINATION COMMITTEE PAGE ...................................................................................... 2 COPYRIGHT PAGE ................................................................................................................ 2 ABSTRACT ............................................................................................................................ 4 ACKNOWLEDGEMENTS ....................................................................................................... 6 TABLE OF CONTENTS........................................................................................................... 8 LIST OF ABBREVIATIONS ................................................................................................... 11 LIST OF ILLUSTRATIONS..................................................................................................... 12 Chapter