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Optical and Structural Properties of Indium Nitride Epilayers Grown by High-Pressure Chemical Vapor Deposition and Vibrational Studies of ZGP Single Crystal

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Optical and Structural Properties of Indium Nitride Epilayers Grown by High-Pressure Chemical Vapor Deposition and Vibrational Studies of ZGP Single Crystal Georgia State University ScholarWorks @ Georgia State University Physics and Astronomy Dissertations Department of Physics and Astronomy 12-7-2012 Optical and Structural Properties of Indium Nitride Epilayers Grown by High-Pressure Chemical Vapor Deposition and Vibrational Studies of ZGP Single Crystal Ramazan Atalay Follow this and additional works at: https://scholarworks.gsu.edu/phy_astr_diss Recommended Citation Atalay, Ramazan, "Optical and Structural Properties of Indium Nitride Epilayers Grown by High-Pressure Chemical Vapor Deposition and Vibrational Studies of ZGP Single Crystal." Dissertation, Georgia State University, 2012. https://scholarworks.gsu.edu/phy_astr_diss/60 This Dissertation is brought to you for free and open access by the Department of Physics and Astronomy at ScholarWorks @ Georgia State University. It has been accepted for inclusion in Physics and Astronomy Dissertations by an authorized administrator of ScholarWorks @ Georgia State University. For more information, please contact [email protected]. OPTICAL AND STRUCTURAL PROPERTIES OF INDIUM NITRIDE EPILAYERS GROWN BY HIGH-PRESSURE CHEMICAL VAPOR DEPOSITION AND VIBRATIONAL STUDIES OF ZGP SINGLE CRYSTAL by RAMAZAN ATALAY Under the Direction of Nikolaus Dietz ABSTRACT The objective of this dissertation is to shed light on the physical properties of InN epilayers grown by High-Pressure Chemical Vapor Deposition (HPCVD) for optical device applications. Physical properties of HPCVD grown InN layers were investigated by X-ray diffraction, Raman scattering, infrared reflection spectroscopies, and atomic force microscopy. The dependencies of physical properties as well as surface morphologies of InN layers grown either directly on sapphire substrates or on GaN/sapphire templates on varied growth conditions were studied. The effect of crucial growth parameters such as growth pressure, V/III molar ratio, precursor pulse separation, substrate material, and mass transport along the flow direction on the optical and structural properties, as well as on the surface morphologies were investigated separately. At present, growth of high-quality InN material by conventional growth techniques is limited due to low dissociation temperature of InN (~600 ºC) and large difference in the partial pressures of TMI and NH3 precursors. In this research, HPCVD technique, in which ambient nitrogen is injected into reaction zone at super-atmospheric growth pressures, was utilized to suppress surface dissociation of InN at high temperatures. At high pressures, long-range and short-range orderings indicate that c-lattice constant is shorter and E2(high) mode frequency is higher than those obtained from low-pressure growth techniques, revealing that InN structure compressed either due to a hydrostatic pressure during the growth or thermal contraction during the annealing. Although the influence of varied growth parameters usually exhibit consistent correlation between long-range and short-range crystalline orderings, inconsistent correlation of these indicate inclination of InN anisotropy. InN layers, grown directly on α-sapphire substrates, exhibit InN (1 0 1¯ 1) Bragg reflex. This might be due to a high c/a ratio of sapphire-grown InN epilayers compared to that of GaN/sapphire-grown InN epilayers. Optical analysis indicates that free carrier concentration, ne, in the range of 1–50 × 1018 cm–3 exhibits consistent tendency with longitudinal-optic phonon. However, for high ne values, electrostatic forces dominate over inter-atomic forces, and consistent tendency between ne and LO phonon disappears. Structural results reveal that growth temperature increases ~6.6 ºC/bar and V/III ratio affects indium migration and/or evaporation. The growth temperature and V/III ratio of InN thin films are optimized at ~850 ºC and 2400 molar ratio, respectively. Although high in-plane strain and c/a ratio values are obtained for sapphire-grown epilayers, FWHM values of long-range and short-range orderings and free carrier concentration value are still lower than those of GaN/sapphire-grown epilayers. Finally, vibrational and optical properties of chalcopyrite ZGP crystal on the (001), (110), and (1¯10) crystalline planes were investigated by Raman scattering and infrared (IR) reflection spectroscopies. Raman scattering exhibits a nonlinear polarizability on the c-plane, and a linear polarizability on the a- and b-planes of ZGP crystal. Also, birefringence of ZGP crystal was calculated from the hydrostatic pressure difference between (110) and (1¯10) crystalline planes for mid-frequency B2(LO) mode. INDEX WORDS: Group III-nitrides, Indium nitride (InN), High-Pressure Chemical Vapor Deposition (HPCVD), Raman scattering spectroscopy, Infrared (IR) reflection spectroscopy, and X-ray diffraction OPTICAL AND STRUCTURAL PROPERTIES OF INDIUM NITRIDE EPILAYERS GROWN BY HIGH-PRESSURE CHEMICAL VAPOR DEPOSITION AND VIBRATIONAL STUDIES OF ZGP SINGLE CRYSTAL by RAMAZAN ATALAY A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the College of Arts and Sciences Georgia State University 2012 Copyright by Ramazan Atalay 2012 OPTICAL AND STRUCTURAL PROPERTIES OF INDIUM NITRIDE EPILAYERS GROWN BY HIGH-PRESSURE CHEMICAL VAPOR DEPOSITION AND VIBRATIONAL STUDIES OF ZGP SINGLE CRYSTAL by RAMAZAN ATALAY Committee Chair: Nikolaus Dietz Committee: Brian D. Thoms Vadym Apalkov Murad Sarsour Douglas R. Gies Electronic Version Approved: Office of Graduate Studies College of Arts and Sciences Georgia State University December 2012 iv This thesis is dedicated to my loving family, Ömer, Fatma, Nurşen, and Gülşen, and my brothers-in-law, Ahmet and Ömer, for their endless love, encouragement, support, and sacrifices. v ACKNOWLEDGMENTS First and foremost, I would like to express my deepest appreciation to my committee chair, Professor Nikolaus Dietz, who continuously and convincingly conveyed a spirit of academic research and physics teaching to me. His guidance throughout the course of my graduate study here at Georgia State University was indispensable for me to develop research skills. Without his guidance and persistent help to execute academic research from fundamentals of physics and to communicate with the scientific community, this dissertation would not have been possible. I also was extremely fortunate to have the privilege to work in his distinguished research group. I would like to thank my committee members, Professors Brian D. Thoms, Vadym Apalkov, Murad Sarsour, and Douglas R. Gies, whose great enthusiasm for my research, scientific guidance, as well as participation on my dissertation committee was a priceless privilege for me. In addition, I want to express my gratitude to the Department of Physics and Astronomy at the Georgia State University for six-year supporting my works in terms of Graduate Research Assistantship. I recognize that this research would not have been possible without the financial support of Air Force Office of Scientific Research. I am also thankful to Professors Ian T. Ferguson from University of North Carolina Charlotte, Zlatko Sitar from North Carolina State University, Axel Hoffmann from Technical University Berlin, and A. G. U. Perera from Georgia State University and their group members for doing characterization of materials and providing scientific feedback that we need most. vi Next, I am indebted to my life-long friend and colleague Dr. Goksel Durkaya for his encouragement and friendship throughout my years at Georgia State and Middle East Technical University. Goksel had first-hand knowledge of what was Ph.D. process and what I was experiencing. This understanding was priceless for both of us through the Ph.D. process. Special thanks go to Dr. Mustafa Alevli, Dr. Max Buegler, Mr. Sampath Gamage, Ms. M. K. Indika Senevirathna, Mr. Rasanga Samaraweera, and Ms. Kasuni Nanayakkara of the members of NALD research group who have been my co-workers for three years deserve an untold amount of appreciation for their friendship and making the working environment so supportive. Ramiz, Fatima, Edna, and Edin Osmanbasic and Ismet, Elsa, Dzenan, Nedzad, and Hasan Redzic, thank you so much for your great hospitality, friendly conversation, yummy food, and great conversation on many topics and for support during the hectic times when I needed most to finish my Ph.D. process. It really helped me to keep perspective on what really matters and what does not. Last, but certainly not least, I would like to thank my family members for their unconditional love and support. They have always supported my interests even when they did not know what I was doing. My parents, Omer and Fatma, my sisters, Nursen and Gulsen, and my brothers in law, Ahmet and Omer have helped to keep me sane throughout my education and have taught me the virtues of perseverance and hard work; two priceless talents of life. Finally, I am grateful to two names, engraved in my heart, more than anyone else. vii TABLE OF CONTENTS ACKNOWLEDGMENTS .............................................................................................................v LIST OF TABLES .........................................................................................................................x LIST OF FIGURES ................................................................................................................... xiv 1. MOTIVATION AND OUTLINE OF RESEARCH ............................................................1 1.1. Motivation of Research ..................................................................................................1
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