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The Growth and Characterization of Gallium Arsenide Nanowire Structures by Metal Organic Chemical Vapor Deposition

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The Growth and Characterization of Gallium Arsenide Nanowire Structures by Metal Organic Chemical Vapor Deposition The Growth and Characterization of Gallium Arsenide Nanowire Structures by Metal Organic Chemical Vapor Deposition DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Nicholas G. Minutillo Graduate Program in Physics The Ohio State University 2014 Dissertation Committee: Professor Fengyuan Yang, Advisor Professor Jay A. Gupta Professor Klaus Honscheid Professor Mohit Randeria Copyright by Nicholas Gaetano Minutillo 2014 Abstract Semiconductor nanowires hold a wealth of promise for studying the fundamental physics of electron behavior and interactions in a quasi-one dimensional environment as well as components in or the foundation of technological advancement in electronic and spintronic devices. Especially in the case of spintronic applications, the crystalline environment must be highly controlled. Unlike in electronic devices, predicated on the transport or storage of charges, spintronic devices often depend on relative phases of spin states. These phases are easily lost in an environment where scattering probabilities are high. In any material system, control of the material fabrication is the limiting factor to achieving the theoretical characteristics and operation. Still an active area of research, bottom-up synthesis of semiconductor nanowires has yet to reach the level of control required for wide spread adoption as a base system in condensed matter research. At this point in time, the material synthesis to meet the criteria for advanced applications remains a bottle neck in advancing the application of GaAs or any other semiconductor nanowires. In this dissertation we discuss the vapor-liquid-solid (VLS) mechanism and its role in the growth of gallium arsenide and other III-V semiconductors. The VLS mechanism has become a foundation of bottom-up nanowire growth. We will further discuss metal organic chemical vapor deposition (MOCVD), an epitaxial technique ii developed for III-V semiconductor thin films that has risen to prominence in the field of nanowire growth. The physics that governs the VLS growth of GaAs nanowires is the subject of ongoing research. We systematically analyze the effect of core-growth temperature on VLS, epitaxial GaAs/AlGaAs core/shell nanowires in MOCVD by photoluminescence characterization of nanowire ensembles as a function of core growth temperature. To our knowledge, a systematic study of the photoluminescence dependence on growth temperature prior to ours does not exist in the peer-reviewed literature. We demonstrate photoluminescence linewidths on ensembles of nanowires that are competitive with the best single-wire linewidths reported in the literature. We thus demonstrate wires of highly uniform characteristics across the entire growth surface. Our results also indicate that the effect of the core growth temperature is coupled to the crystal orientation of the substrate surface. At low growth temperatures, nanowires grown on a GaAs (100) surface exhibit a narrower photoluminescence peak at the band edge in a wider growth temperature window than do the wires grown on a GaAs (111)B surface. This is contrary to what might be expected given that all the wires grow in the <111> direction and display the same growth rate on both substrate surfaces. Under the conditions used, the window in growth temperature for a high optical quality gallium arsenide core nanowire is narrow compared to common conditions in thin film epitaxy by MOCVD. We discuss our methods for the successful growth of a novel nanowire device structure by MOCVD. We grow vertical GaAs nanowires and embedded them in a continuous film of AlGaAs. This structure has thus far only been reported in molecular iii beam epitaxy, which by its directional nature, more naturally lends itself growth in high aspect ratio channels. In addition to being relatively uncommon, this structure has several advantages. First, the 40 nm diameter GaAs nanowires are protected by the in situ AlGaAs growth. Second, the geometry allows the use of thin film techniques for device processing to easily control the number of wires to be activated in the device by simply changing the area of the patterned contact. Development of this nanowire-thin-film geometry opens the door for the study of parallel ensembles of nanowires and nanowire heterostructures. iv Dedication To Gaetano Minutillo and Anthony Laudati v Acknowledgments I must first thank my advisor, Professor Fengyuan Yang for his guidance, support, and patience as I navigated my way through graduate research. I am fortunate to have had the opportunity to work in his lab and learn about semiconductor physics and be granted access and exposure to many areas of semiconductor science in both the academic and industrial realm. Above all, I have learned that crystal growth requires a unique combination of determination, patience, impatience, and resilience. Many thanks to Professor Zeke Johnston-Halperin, who has treated me like one of his own students throughout our collaboration and who has been a provider of helpful insights and perspectives. Thank you to Dr. John Carlin who taught me not only about semiconductor physics, but about the industry as well. His perspective as a scientist who straddles and succeeds in both worlds of semiconductor science remains invaluable to me as I move forward. Thank you for answering your phone at 2 am to help me bring the MOCVD out of an alarm state. Thank you to Yi-Hsin Chiu, my longest and most patient collaborator at OSU. I thank her for all the conversations about physics and about life, for her level headed demeanor and for her tireless efforts to measure every sample I could throw at her. vi I would like to further thank all the scientists who have lent me their invaluable time and expertise for my own edification and to the data contained herein. Thank you to Rob Williams and Professor Dave McComb for working with us and imaging our nanowires with both of their best (and coolest) STEM instruments. Thank you also to Dr. Camelia Selcu, who began our conductive AFM and gave me her expert advice as we continue on with the technique on our own. Thank you for your patience and hard work. Thank you to Adam Hauser for always being a positive source of encouragement and acting as a role model worthy of emulation. Thanks to Brian Peters for our many late night/early morning conversations and helping me keep my sanity when things went awry. Thank you to Jeremy Lucy for having a remarkable strength of character. For saying what needs to be said, but also staying around to help fix whatever needs fixing, either broken instruments or broken morale. Thanks to James Gallagher for his unique and always sincere perspective. Thanks to Hailong who has proven the value of relentless hard work. Thank you to Greg Smith for his contributions to both this project and myself as a scientist. I wish you all the best in your new group and I hope that you carry with you the tradition of bad jokes I have tried so hard to instill. Thank you to Mark Patrick, Megan Harberts, Ula Szafruga, Yaser Helal, and Richelle Teeling-Smith for your friendships throughout this journey we call graduate school. Thank you to Tricia Meyer for all of your loving support. Thank you for being the voice of calm, reason, and compassion when I needed it the most and seeing in me what I might otherwise not have seen myself. Thank you to Professor Paul Angiolillo for believing in me from the moment I said I wanted to study physics, halfway through my vii college career. Thank you for enabling me to make the step into graduate studies and for supporting me as a friend and a mentor the entire way. Thank you to Andrzej Latka for going on this adventure with me, for pushing me outside of my comfort zone, and for being the most loyal and true friend a person could hope to find. Finally thank you to my parents Angelo and Mary Ann and my sister Madeleine for supporting me in this and every chapter of my life. I could not have made it this far without your love and support, help through the growing pains and the triumphs. Thank you for keeping me grounded and giving me the confidence to push through the tough times. Thank you for helping me put everything in the proper perspective and allowing me to believe that my aspirations are possible. Above all thank you to my parents for every sacrifice you have made to provide us the environment and opportunity to achieve whatever level of education or career path we most desire. viii Vita May 2004 .......................................................Saint Joseph’s Preparatory School December 2008 ..............................................B.S. Physics, Saint Joseph’s University August 2011 ...................................................M.S. Physics, The Ohio State University September 2009 to June 2009 .......................Graduate Teaching Associate, Department of Physics, The Ohio State University June 2009 to August 2013 .............................Graduate Research Associate, Department of Physics, The Ohio State University September 2013 to present ............................Graduate Teaching Associate, Department of Physics, The Ohio State University ix Publications Nicholas G. Minutillo, Yi-Hsin Chiu, Robert E.A. Williams, Greg J. Smith, David W. McComb, John A. Carlin, Ezekiel Johnston-Halperin, Fengyuan Yang, Photoluminescence and Morphology Evolution in GaAs/AlGaAs Core/Shell Nanowires Grown by MOCVD: Effects of Core Growth Temperature – Submitted Fields
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