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Silicon-Based Infrared Photodetectors for Low-Cost Imaging Applications

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Silicon-Based Infrared Photodetectors for Low-Cost Imaging Applications SILICON-BASED INFRARED PHOTODETECTORS FOR LOW-COST IMAGING APPLICATIONS Dissertation Submitted to The School of Engineering of the UNIVERSITY OF DAYTON In Partial Fulfillment of the Requirements for The Degree of Doctor of Philosophy in Electro-Optics Joshua Duran, M.S. Dayton, Ohio May 2019 SILICON-BASED INFRARED PHOTODETECTORS FOR LOW-COST IMAGING APPLICATIONS Name: Duran, Joshua APPROVED BY: ________________________________ ________________________________ Andrew Sarangan, Ph.D. Michael Eismann, Ph.D. Advisory Committee Chair Committee Member Professor, Dept. of Electro-Optics & Photonics Chief Scientist, AFRL/RY ________________________________ ________________________________ Jay Mathews, Ph.D. Partha Banerjee, Ph.D. Committee Member Committee Member Assistant Professor, Department of Physics Professor, Dept. of Electro-Optics & Photonics ________________________________ David Forrai, M.S. Committee Member Program Manager, DARPA ________________________________ ________________________________ Robert J. Wilkens, Ph.D., P.E. Eddy Rojas, Ph.D., M.A., P.E. Associate Dean for Research and Innovation Dean of School of Engineering Professor School of Engineering ii ABSTRACT SILICON-BASED INFRARED PHOTODETECTORS FOR LOW-COST IMAGING APPLICATIONS Name: Duran, Joshua University of Dayton Advisor: Dr. Andrew Sarangan Infrared imaging is a powerful capability that has been technologically driven primarily by the defense industry over the past several decades. As a result, ultra-high-performance infrared imaging arrays with specialized functionality have been developed but at a relatively high cost. Meanwhile, economy of scale has driven the price of visible complementary metal- oxide-semiconductor (CMOS) image sensors down drastically while simultaneously providing greater on-chip capability and performance. Silicon-based infrared sensors have the potential to leverage modern CMOS advancements and cost, but poor performance has inhibited the widespread adoption of this technology. In this work, I explored the potential for novel silicon- based infrared sensors that exploit nanoscale structures to provide new methods of photodetection in silicon beyond the bulk bandgap response. Nanostructure fabrication developments and challenges were also investigated with the perspective of applying the underlying structure as a platform to detect infrared photons. Proposed solutions include improvement to existing detector technology (Schottky barrier photodiodes) as well as novel detector architectures (silicon quantum walls) that leverage the unique geometry of nanostructured silicon. iii ACKNOWLEDGEMENTS I would like to first thank my advisor, Dr. Andrew Sarangan, for his guidance, mentorship and professional insight during this project and throughout my time as a graduate student. I first met Dr. Sarangan while working with him over the summer break on an undergraduate research project. I spent the summer working in the cleanroom with him, and he left a tremendous impression on me in that short time. That experience ultimately led to my decision to pursue graduate school, with the desire to continue working with and learning from him. I am grateful for the opportunity I’ve had to work with Dr. Sarangan and thankful he invited me to work with him that summer. I admire his ability to translate complex concepts into digestible pieces and his fearlessness and excitement when taking on a new challenge, regardless of the unknowns. I hope to continue our relationship through collaborative research efforts in the future. I also have my committee members to thank, for their feedback from my prospectus, where they identified several missing elements of the project and helped me focus the variety of concepts I had into a more cohesive and manageable project. I want to also thank them for the time they spent reviewing and improving this document and for the guidance they’ve provided me throughout this process. For the duration of this project, I’ve been employed by the Air Force Research Laboratory as a research engineer focused on IR detectors for imaging applications. Many of my coworkers at AFRL have helped me both directly and indirectly on this project, too many to list iv here. Having said that, I would like to highlight several people who have directly helped me on various aspects of this project: Jason Hickey for performing the metal depositions and for his help in calibrating the ultra-thin film deposition rate, Andy Browning for performing the PECVD processes, Kevin Leedy for teaching me about the ALD process and for training me on the tool, Mike Eismann, who is also a committee member, for hosting several meetings with me to discuss my ideas and progress throughout the project, and Gamini Ariyawansa for his insightful discussions on the phenomenology of quantum wells and walls and for aiding me with the modeling section of Chapter 3. Finally, I would like to thank my wife, parents, brother, sister, family and friends for their continued support. These people have all played a significant role in shaping me into the individual I have become. Any accomplishments I achieve, including the work written here, is a reflection of these people and the love and care they’ve given me throughout my life. v TABLE OF CONTENTS ABSTRACT ........................................................................................................................................ iii ACKNOWLEDGEMENTS ................................................................................................................... iv LIST OF FIGURES ............................................................................................................................... x LIST OF TABLES ............................................................................................................................... xix EXECUTIVE SUMMARY .................................................................................................................... xx CHAPTER 1 BACKGROUND AND MOTIVATION ................................................................................ 1 1.1 The Electromagnetic Spectrum ............................................................................................. 3 1.1.1 Atmospheric Transmission ............................................................................................. 4 1.1.2 Blackbody Radiation ....................................................................................................... 5 1.1.3 Additional Photon Sources ............................................................................................. 6 1.2 Infrared Detector Array Architectures .................................................................................. 8 1.2.1 Hybrid Focal Plane Arrays .............................................................................................. 9 1.2.2 Monolithic Infrared Focal Plane Arrays........................................................................ 14 1.3 Chapter 1 Summary ............................................................................................................ 20 CHAPTER 2 SILICIDE-BASED SCHOTTKY BARRIER PHOTODETECTORS ........................................... 22 2.1 Internal Quantum Efficiency ............................................................................................... 25 vi 2.2 Dark Current ........................................................................................................................ 35 2.3 Device Fabrication ............................................................................................................... 40 2.4 Characterization Setup and Measurement Techniques ..................................................... 45 2.4.1 Housing ........................................................................................................................ 45 2.4.2 Dark Current ................................................................................................................. 47 2.4.3 Spectral Response ........................................................................................................ 49 2.4.4 External Quantum Efficiency ........................................................................................ 53 2.4.5 Reflection, Transmission and Absorption .................................................................... 57 2.5 Device Results ..................................................................................................................... 74 2.5.1 Material Comparison ................................................................................................... 74 2.5.2 Dark Current ................................................................................................................. 80 2.5.3 External Quantum Efficiency ........................................................................................ 84 2.5.4 Optical Characterization .............................................................................................. 85 2.5.5 Internal Quantum Efficiency ........................................................................................ 91 2.5.6 Image Sensor Demonstration ...................................................................................... 95 2.6 Engineering NiSi Schottky Barrier Photodiodes for Improved Quantum Efficiency ........... 99 2.7 Chapter 2 Summary .......................................................................................................... 105 CHAPTER 3 SILICON NANOSTRUCTURES
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