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Molecular Beam Epitaxy Growth of Inn and Ingan Materials Molecular Beam Epitaxy Growth of Indium Nitride and Indium Gallium Nitride Materials for Photovoltaic Applications A Ph.D. Dissertation Presented to The Academic Faculty by Elaissa Trybus In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the School of Electrical and Computer Engineering Georgia Institute of Technology May 2009 Copyright 2009 by Elaissa Trybus Molecular Beam Epitaxy Growth of Indium Nitride and Indium Gallium Nitride Materials for Photovoltaic Applications Dr. W. Alan Doolittle School of Electrical and Computer Engineering Georgia Institute of Technology Dr. Ian Ferguson School of Electrical and Computer Engineering Georgia Institute of Technology Dr. Ajeet Rohatgi School of Electrical and Computer Engineering Georgia Institute of Technology Dr. Shyh-Chiang Shen School of Electrical and Computer Engineering Georgia Institute of Technology Dr. Samuel Graham School of Mechanical Engineering Georgia Institute of Technology Date Approved: March 2009 ii To my parents. This would not have been possible without your support. iii Go confidently in the direction of your dreams. Live the life you’ve imagined. -Henry David Thoreau iv ACKNOWLEDGEMENTS My interest in math and science was fostered by my Dad, the Physicist. I would not be an Electrical Engineer (AKA an applied Physicist) without his instruction and support. I thank both my parents for their never ending love and support. My advisor, Dr. W. Alan Doolittle has been very supportive, patient, and provided me with endless knowledge. I am extremely grateful to him. Additionally, the members of his research group have been invaluable to me in friendship and with my education: Walter Henderson, David Pritchett, Alex Carver, Daniel Billingsley, Laws Calley, Michael Moseley, Kyoung Keun Lee, Ann Trippe, Dr. Gon Namkoong, and Dr. Shawn Burnham. I also thank Dr. Doolittle’s Accountant Mary Render and Administrative Assistant Linda Newton. I would like to acknowledge the support and guidance received from my thesis committee and the friendship from their research groups: Dr. Ian Ferguson, Dr. Shyh- Chiang Shen, Dr. Ajeet Rohatgi, and Dr. Samuel Graham. In addition, I would like to thank Dr. Christiana Honsberg of the University of Delaware and her research group, in particular Dr. Omkar Jani and Balakrishnam Jampana. The MiRC staff has been very helpful and accommodating with my research, specifically Gary Spinner, Charlie Suh, Vinh Nguyen, and Dean Sutter. Throughout my graduate studies at Georgia Tech I have had the support of many friends and family: my sister Brittany, my best friends since high school Emily Gaffney, Emm Starnes, and Keely Hogan-Braker, my extended family of grandparents, aunts, uncles, and cousins – The Trybus, Burton, and Korenkiewicz families, the SwimAtlanta v family at Georgia Tech - Doug Gjersten and Sergey Useinov, Bill and Jenny Eversole, Gus who has been there everyday, Arti who always makes me laugh, and the Hardy family, especially George. Thank-you. This work was supported by the Defense Advance Research Project Agency, monitored by Dr. Doug Kirpatrick, Dr. Brian Pierce, and Dr. Stefanie Tompkins under the University of Delaware-DuPont Very High Efficiency Solar Cell program monitored by Dr. Dan Laubacher and Dr. Allen Barnett. vi TABLE OF CONTENTS ACKNOWLEDGEMENTS ..............................................................................................v LIST OF TABLES ........................................................................................................... ix LIST OF FIGURES ...........................................................................................................x SUMMARY ................................................................................................................... xvii CHAPTER 1: Introduction...............................................................................................1 1.1. Solar Cells.......................................................................................................... 1 1.1.1. Test Procedures.......................................................................................................................4 1.2. III-N Materials .................................................................................................. 7 1.2.1. Bandgap Values......................................................................................................................8 1.2.2. InN and GaN Phase Separation.............................................................................................9 1.2.3. Polarization and Piezoelectric Effects .................................................................................10 1.3. Molecular Beam Epitaxy................................................................................ 13 1.3.1. In-Situ Characterization Techniques...................................................................................14 CHAPTER 2: Growth of InN .........................................................................................16 2.1. Growth of InN on Germanium Substrates ................................................... 16 2.1.1. Growth Conditions and Analysis..........................................................................................17 2.1.2. Epitaxial Al Interconnect Layer...........................................................................................22 2.2. The Bandgap Value of InN............................................................................. 26 2.2.1. Growth Conditions and Analysis..........................................................................................26 2.3. Summary.......................................................................................................... 32 CHAPTER 3: Growth and Characteristics of InxGa1-xN Epitaxial Layers................33 3.1. Characteristics of InxGa1-xN Epitaxial Layers ............................................. 34 3.1.1. Growth Conditions and Analysis..........................................................................................34 3.1.1.1. Compositional Phase Separation.....................................................................................35 3.1.1.2. Optical Measurements to Determine Absorption Coefficients .......................................37 3.2. P-type InxGa1-xN Limitations......................................................................... 39 3.3. Effects of Large Mg flux in Mg-doped InxGa1-xN ........................................ 43 3.3.1. Crystallographic Structure ...................................................................................................43 3.3.2. Growth Conditions and Analysis..........................................................................................44 3.4. Effects of Low Mg Flux in Mg-doped InxGa1-xN.......................................... 49 3.4.1. Growth Conditions and Structural Analysis............................................... 49 3.4.2. Electrical Analysis........................................................................................ 52 3.5. Summary.......................................................................................................... 53 CHAPTER 4: Metal Modulation Epitaxy Growth of Doped GaN..............................55 4.1. Systematic Study of Mg-doped GaN ............................................................. 56 4.1.1. Growth Conditions and Analysis..........................................................................................58 4.1.1.1. Hall and XRD Results......................................................................................................64 4.1.1.2. Atomic Force Microscopy Results...................................................................................71 4.2. Annealing Study of High Hole Concentration Mg-doped GaN.................. 73 4.3. Systematic Study of Si-doped GaN................................................................ 74 4.4. Summary.......................................................................................................... 75 vii CHAPTER 5: Metal Modulated Epitaxy Growth of InN and InxGa1-xN ...................77 5.1 Mg-doped InN ................................................................................................. 78 5.1.1 Growth Conditions and Analysis..........................................................................................80 5.2 Summary.......................................................................................................... 84 CHAPTER 6: InxGa1-xN Solar Cell................................................................................85 6.1. SiLENSe........................................................................................................... 85 6.1.1. Band Diagrams.....................................................................................................................87 6.1.2 SiLENSe Parameters............................................................................................................90 6.1.3 Dark Current-Voltage Simulations......................................................................................93 6.2. Growth Conditions.......................................................................................... 97 6.3. Fabrication Results ....................................................................................... 100 6.3.1. Mask Layout .......................................................................................................................100
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