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THERMODYNAMICS of POST-GROWTH ANNEALING of CADMIUM ZINC TELLURIDE NUCLEAR RADIATION DETECTORS by AARON LEE ADAMS MARCUS D. AS

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THERMODYNAMICS of POST-GROWTH ANNEALING of CADMIUM ZINC TELLURIDE NUCLEAR RADIATION DETECTORS by AARON LEE ADAMS MARCUS D. AS THERMODYNAMICS OF POST-GROWTH ANNEALING OF CADMIUM ZINC TELLURIDE NUCLEAR RADIATION DETECTORS by AARON LEE ADAMS MARCUS D. ASHFORD, COMMITTEE CHAIR STEPHEN U. EGARIEVWE RALPH B. JAMES DANIEL J. FONSECA K. CLARK MIDKIFF A DISSERTATION Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Mechanical Engineering in the Graduate School of The University of Alabama TUSCALOOSA, ALABAMA 2013 Copyright Aaron Lee Adams 2013 ALL RIGHTS RESERVED ABSTRACT Nuclear Radiation Detectors are used for detecting, tracking, and identifying radioactive materials which emit high-energy gamma and X-rays. The use of Cadmium Zinc Telluride (CdZnTe) detectors is particularly attractive because of the detector’s ability to operate at room temperature and measure the energy spectra of gamma-ray sources with a high resolution, typically less than 1% at 662 keV. While CdZnTe detectors are acceptable imperfections in the crystals limit their full market potential. One of the major imperfections are Tellurium inclusions generated during the crystal growth process by the retrograde solubility of Tellurium and Tellurium-rich melt trapped at the growth interface. Tellurium inclusions trap charge carriers generated by gamma and X-ray photons and thus reduce the portion of generated charge carriers that reach the electrodes for collection and conversion into a readable signal which is representative of the ionizing radiation’s energy and intensity. One approach in resolving this problem is post-growth annealing which has the potential of removing the Tellurium inclusions and associated impurities. The goal of this project is to use experimental techniques to study the thermodynamics of Tellurium inclusion migration in post-growth annealing of CdZnTe nuclear detectors with the temperature gradient zone migration (TGZM) technique. Systematic experiments will be carried out to provide adequate thermodynamic data that will inform the engineering community of the optimum annealing parameters. Additionally, multivariable correlations that involve the Tellurium diffusion coefficient, annealing parameters, and CdZnTe properties will be analyzed. ii The experimental approach will involve systematic annealing experiments (in Cd vapor overpressure) on different sizes of CdZnTe crystals at varying temperature gradients ranging from 0 to 60 oC/mm (used to migrate the Tellurium inclusion to one side of the crystal), and at annealing temperatures ranging from 500 to 800 oC. The characterization techniques that will be used to quantify the effects of the post-growth annealing experiments include: 1) 3D infrared transmission microscopy to measure the size, distribution, and concentration of Tellurium inclusions; 2) current-voltage measurements to determine the effect of post-growth annealing on the resistivity of CdZnTe crystals; and 3) X-ray diffraction topography, available at the National Synchrotron Light Source (NSLS) facilities at Brookhaven National Laboratory (BNL), to measure the correlation between device performance and annealing conditions. iii DEDICATION This dissertation is dedicated to my mother, Mrs. Donna Jean Dickerson Adams; I wish that you were here to share in this accomplishment. I know that this would really make you smile and bake me a lemon pound cake. I really miss those cakes. I love you and miss you with all my heart. To my sisters, Lynn and Paula, who helped me and guided me through the trials and tribulations of life. Thank you for always being there for me, and for standing by me throughout the time taken to complete this masterpiece. I love you both, always. iv LIST OF ABBREVIATIONS AND SYMBOLS HPGe High-Purity Germanium MCA Multi-Channel Analyzer ASME American Society of Mechanical Engineering CdZnTe Cadmium Zinc Telluride TGZM Temperature Gradient Zone Melting Cd Cadmium T Tellurium BNL Brookhaven National Laboratory NSLS National Synchrotron Light Source Ge Germanium keV kiloelectron volt eV electron volt THM Traveling Heater Method IR Infrared IV Current Voltage IDL Interactive Data Language Fe Iron Cr Chromium Al Aluminum Au Gold Cu Copper Ag Silver Mn Manganese Zn Zinc NaI Sodium Iodide CsI Cesium Iodide Z Atomic Number v ACKNOWLEDGMENTS I owe my deepest gratitude to Dr. Marcus D. Ashford, my advisor and chair of my Ph.D. committee, for his encouragement, supervision, and support from my early years at the University of Alabama, through my preliminary and qualifying examinations to the conclusion of this dissertation. I am also very grateful to Dr. Stephen U. Egarievwe, for mentoring me through this research project. I am grateful to Dr. Ralph B. James for providing me with the opportunity to learn and do research with the brightest minds and world-class equipment located at Brookhaven National Laboratory. I would like to specifically thank these three mentors for creating the inter-institutional collaboration involving The University of Alabama, Alabama A & M University, and Brookhaven National Laboratory for the advancement of the science of room- temperature nuclear radiation detector materials. I would like to acknowledge the following institutions for financially supporting me throughout my graduate career: The University of Alabama Mechanical Engineering department, The University of Alabama Future Faculty Fellowship, the National GEM Consortium Fellowship, the GK-12 program and the National Science Foundation (NSF) Grant No. CBET- 1125783, the U.S. Department of Education’s Title III Strengthen Grants Program, the U.S. Department of Energy’s Office of Nonproliferation Research & Development, Treaty Verification (NA-22), the Defense Threat Reduction Agency (DTRA), the Joint U.S. Department of Homeland Security (DHS), the Domestic Nuclear Detection Office (DNDO), the National Science Foundation (NSF) Academic Research Initiative (ARI) Grant No. ECCS-1140059, and the U.S. Nuclear Regulatory Commission (NRC) MSI Grant No. NRC-27-10-514. vi I would also like to acknowledge the other members of my committee, Dr. K. Clark Midkiff and Dr. Daniel Fonseca, for their guidance and availability to help. I especially thank Dr. Midkiff for providing me with teaching assistantships in the early years at The University of Alabama. I would like to express a sincere gratitude to Dr. Ge Yang for introducing and tutoring me on the several processes that are involved in CdZnTe annealing, as well as his mentorship in other research areas. I would also like to thank the entire detector-testing group at the Nonproliferation and National Security Department of Brookhaven National Laboratory: Dr. Anwar Hossain; Mr. Giuseppe Camarda; Dr. Ge Yang; Dr. Yonggang Cui; Dr. Kim; Dr. Aleksey; Mrs. Patty Lee; and my fellow graduate students. I also thank my Alabama A & M University family for their unwavering support: Dr. Andrew Hugine Jr.; Dr. Daniel Wims; Dr. Kevin Rolle; Dr. Chance Glenn Sr.; Mr. Alan Terrill; Dr. Mebougna Drabo; Dr. Aschalew Kassu; Dr. Wing Chan; Dr. Peter Romine; Mr. Eugene Black; Dr. F. Michael Ayokanmbi; Mrs. Y. Dawn Devent; Mr. Gearld Vines; Dr. V. Trent Montgomery; Mr. Archie Tucker; Mrs. Wendy Kolber; Dr. Robert Powell; Mr. Rodney Pinder; and Ms. Valissa Sams. A sincere thanks to Ms. Tikyna Dandridge for always listening. Last but not least, my family at The University of Alabama: Mr. Joshua Tolbert; Mr. Ben Tolbert; Dr. Tanisha Booker; Dr. Tad Driver; Mr. Anar Thors; Mr. Mike Alff; Mr. John Crawford; Mrs. Lisa Hinton; Dr. John Baker; Dr. Keith Williams; Dr. Steven Kavanaugh; Dr. Steven Shepard; and Ms. Lynn Hamric. I also want to give a special thanks to my cousin, Mr. Albert Dean Wilson and his family, for making my transition from Michigan to Alabama go so smoothly, and for providing support in any matter necessary to see me through to the finish line. This research would not be possible without my collaborators, fellow graduate students and friends who have worked countless hours with me, and in doing so shared laboratories, equipment, office spaces, lunches, and stories. Last but not least, I would vii like to thank my family, especially Ted Adams, for all the late night emails and phone calls, who never stopped encouraging me to persist and complete this journey. viii TABLE OF CONTENTS ABSTRACT .................................................................................................................................... ii DEDICATION ............................................................................................................................... iv LIST OF ABBREVIATIONS AND SYMBOLS ............................................................................v ACKNOWLEDGMENTS ............................................................................................................. vi LIST OF TABLES ........................................................................................................................ xii LIST OF FIGURES ..................................................................................................................... xiii CHAPTER ONE: HISTORY AND MOTIVATION ......................................................................1 Overview ..............................................................................................................................1 History of Radiation .............................................................................................................1 Early Radiation Detection Methods .....................................................................................2 Semiconductors
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