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Heterojunction Engineering for Next Generation Hybrid II-VI Materials City University of New York (CUNY) CUNY Academic Works All Dissertations, Theses, and Capstone Projects Dissertations, Theses, and Capstone Projects 9-2017 Heterojunction Engineering for Next Generation Hybrid II-VI Materials Thor Garcia The Graduate Center, City University of New York How does access to this work benefit ou?y Let us know! More information about this work at: https://academicworks.cuny.edu/gc_etds/2385 Discover additional works at: https://academicworks.cuny.edu This work is made publicly available by the City University of New York (CUNY). Contact: [email protected] HETEROJUNCTION ENGINEERING FOR NEXT GENERATION HYBRID II-VI MATERIALS by THOR AXTMANN GARCIA A dissertation submitted to the Graduate Faculty in chemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy, The City University of New York 2017 © 2017 THOR AXTMANN GARCIA All Rights Reserved ii Heterojunction Engineering for Next Generation Hybrid II-VI Materials by Thor Axtmann Garcia This manuscript has been read and accepted for the Graduate Faculty in chemistry in satisfaction of the dissertation requirement for the degree of Doctor of Philosophy. Date Professor Maria C. Tamargo Chair of Examining Committee Date Professor Brian R. Gibney Executive Officer Supervisory Committee: Professor Aidong Shen Professor Igor L. Kuskovsky Professor Glen Kowach THE CITY UNIVERSITY OF NEW YORK iii ABSTRACT Heterojunction Engineering for Next Generation Hybrid II-VI Materials by Thor Axtmann Garcia Advisor: Professor Maria C. Tamargo Molecular Beam Epitaxy(MBE) is a versatile thin film growth technique with monolayer control of crystallization. The flexibility and precision afforded by the technique allows for unique control of interfaces and electronic structure of the films grown. This facilitates the realization of novel devices and structures within a research environment normally only achieved though complex industrial processes. In the past, the control of each interface in MBE has been explored to great benefit. In this work, we study the control of these interfaces so as to increase the performance of novel devices material systems. This dissertation focuses on two iv main areas in which to manipulate interfaces for our benefit: II-VI Intersuband(ISB) devices and II-VI/Bi2Se3 heterostructures. Intersuband(ISB) devices, such as quantum cascade(QC) lasers and QC detectors operating in the infrared range, were first realized with this technique. ISB devices offer critical advantages over interband devices especially in the infrared and terahertz range. ISB devices present extremely flexible parameter space for design as they are based on thicknesses of quantum wells(QWs) rather than intrinsic properties of the materials. QC lasers II-VI materials support shorter wavelengths in the infrared than do commercially available III-V materials. ZnCdSe/ZnCdMgSe lattice matched to InP allows for QC laser designs to reach up to 2µm due to a conduction band offset of 1.12eV. Also, the relatively high effective mass and the before mentioned conduction band offset make them attractive for QC detectors. Our research demonstrates that with the use of interface control, novel high performance detectors can be achieved within this material system. Additionally, we consider the future of this material system by exploring MgSe/ZnCdSe short period superlattices as a plausible replacement for ZnCdMgSe in these types of devices. v Topological insulators, a new class of materials, have recently attracted a great deal of attention in the scientific community. Among these, Bi2Se3 has a near ideal Dirac cone at the Γ point. Here we demonstrate this material in heterostructures with II-VI semiconductors in order to set the foundation for a new material system for both physical and possible device applications. We also investigate using Bi2Se3 as a virtual substrate for II-VI materials. vi Acknowledgements Acknowledgments: A crystal flake does not heed to the whims of the wind and pen snow. There is no singular endeavor in the entirety of the human line that has one face. Thus, this work is caused not from my will alone but the efforts and inspiration of many. The other flakes whisper through every letter and every data point until each breath is one consciousness contained in these pages. Some crystals with hopes and genius inspire, others are the wind that guide us, and yet more are the partners that settle with you on the ground of science. So now by necessity of precision I will dawn a few names to the blizzard that created this venture. I know more will demand with their sorrow my lack of their celebrity upon this page; it cannot be helped and should not be helped. I urge you to accept this token, if your genius is imbedded within the leaf, please know and are urged to know my gratefulness. First is Maria Tamargo, whose friendship, knowledge, hard work and wisdom led me though this journey. Notwithstanding my many difficulties you never stopped believing in my ability to complete my research and this dissertation task. Through every leak, malfunctioning substrate heater and peculiar lab result you were there to guide me. You never let MBE “beat” me even when I had another failed QCL or contaminated sample. Next time it is Lincoln’s birthday, I will work not to honor him but all the hard work you have given me and the many other students that have had the pleasure of working with you. To the rest of the committee, Aidong Shen, Igor L. Kuskovsky and Glen Kowach who supported me with guidance and wisdom throughout my studies, you have my thanks. vii To my colleagues, none absent would yield a dissertation. To Richard Mough, whose conversations and knowledge stimulated this task. Vasilios Deligianakis, with whom I began and ended the journey. Joel de Jesus, whose genius and work lives strong within these pages. Zhiyi Chen, who pushed me to turn a side project into two momentous chapters. Aidong Shen, who led always with a smile and never once inflicted anything but one in me. Without you I would be growing material in a chamber without vacuum surely. Sidarth and Guepang, who, in numerous conversations and discussions, allowed their brilliance to spread in me. And our collaborators, Arvind Ravikumar and Claire F. Gmachl, who are the giants who gave me shoulders to stand on. Last, the many students who constantly remind me of why I enjoy science. To my family, I am forever grateful. Annette and Elbert Axtmann, who by circumstance held the hope of my academic achievement in their hearts until sailing to the stars, now have their wish. Ann Axtmann, who alone could not help but dream that a hindered dyslexic child could possibly achieve more than a high school diploma. I know the sacrifices to make this happen are so numerous that all I can say is thank you. Even now your efforts live in these pages as you helped me craft the words of this work. Maria Pacis, who embraced her dreams and her rest and in love gave way to mine. The keyboard does not yield to the gratitude you beget in my heart, so I hope you know how I feel. Odin Garcia, who managed despite my many absences to become a loving, caring boy. Giselle Garcia, who missed most of my instruction, held strong and shines brilliantly. Veronica Pacis, who took the void and supported us all so this would be possible. viii Table of Contents Table of Contents ABSTRACT iv Acknowledgments: vii List of Tables and Figures xi 1 Introduction 1 1.1 Overview ...................................................................................................................................... 1 1.2 Molecular Beam Epitaxy .............................................................................................................. 5 1.3 Parameters for Epitaxy .............................................................................................................. 11 1.3.1 Lattice Constant .................................................................................................................... 12 1.3.2 Surface Energy ....................................................................................................................... 15 1.3.3 Thermodynamic Stability ...................................................................................................... 16 1.3.4 Symmetry .............................................................................................................................. 17 1.4 Theoretical Calculations and Modeling ..................................................................................... 18 1.4.1 Structural Simulation Utilizing Density Functional Theory(DFT) ........................................... 19 1.4.2 Band Engineering Calculations for Heterostructure Design ................................................. 21 1.5 Materials and Device Applications ............................................................................................ 24 1.5.1 Intersuband(ISB) devices ....................................................................................................... 25 1.5.2 Quantum Cascade(QC) lasers ................................................................................................ 25 1.5.3 Quantum Cascade(QC) detectors .......................................................................................... 28 1.5.4 Topological Insulators ........................................................................................................... 28 1.6 Characterization .......................................................................................................................
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