PAMBE Growth and Characterization of Superlattice Structures in Nitrides THESIS Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Jing Yang Graduate Program in Materials Science and Engineering The Ohio State University 2013 Dissertation Committee: Dr. Roberto C Myers (advisor) Dr. Siddharth Rajan Dr. Wolfgang Windl Dr. Jay Gupta Copyright by Jing Yang 2013 Abstract Superlattice structures formed using the III- nitrides family of semiconductors have attracted a great deal of attention due to some unique properties. Within the III- nitrides, the large conduction band offset between GaN/AlN and InN/AlN provides very large electron confinement that could be useful for ultrafast intersubband–based photonics. Second, the large spontaneous polarization difference at any nitrides heterostructure interface coupled with the large lattice mismatch (3%-13%), shows the potential for polarization-driven applications. Finally, the epitaxial integration of rare earth pnictides (RE-Pn), such as ErAs and ErSb, in III-As semiconductors has been intensively studied due to the applications in novel high speed photodetectors and photoconductive switches. They motivate the parallel work of embedding GdN in a GaN matrix such as a superlattice structure. In the first part of this thesis, the growth of InN/AlN multiple quantum well structures by plasma assisted molecular beam epitaxy is presented. The InN/AlN multiple quantum wells are grown on top of coalesced AlN nanocolumns on Si(111) substrates. The structural and optical properties of InN/AlN quantum wells are thoroughly studied by scanning transmission electron microscopy, x-ray diffractometry and photoluminescence. STEM confirms the formation of InN quantum wells between AlN barriers. XRD data indicate the successful tuning of the ultra-thin InN quantum well thicknesses from sample II to sample. Photoluminescence measurements show emission in the visible that shifts as a function of quantum well thickness. Moreover, the time decay of PL from the different quantum wells is detected by time correlated single photon counting. In order to study the effects of growth conditions on interface sharpness in GaN/AlN superlattices, we investigate the possibility and demonstrate the success of using growth temperature above the GaN decomposition during the deposition of GaN/AlN superlattices in the second part this work. This high temperature growth condition is compared to well-established low temperature conditions. For superlattices grown thinner than their critical thickness, the N-rich high-temperature sample displays slightly superior structural quality. Reciprocal space mapping has been conducted to study the different relaxation mechanisms in high temperature and low temperature growth conditions. In the third part of the thesis, we report on the integration of the RE-Pn GdN as discrete particles in a GaN matrix, as well as the formation of a GdN/GaN superlattice structure. It is hypothesized that the growth of GdN particles proceeds in a similar fashion to that of Re-Pn in III-As zincblende systems, with initial Re-Pn island formation followed by overgrowth of the surrounding uncovered III-As matrix. Periodic structures of GdN nano-island layers spaced between GaN regions were prepared and subsequently characterized by a variety of methods. High resolution XRD shows that the cubic rock- salt GdN islands are epitaxially oriented to the hexagonal wurtzite GaN matrix with the relationship GdN [111]||GaN[0001] with 2.4 ML GdN deposit. Cross-sectional STEM III combined with in-situ reflection high-energy electron diffraction allows for the study of island formation dynamics, which occurs after 1.2 monolayers of GdN coverage. IV Dedication This document is dedicated to my parents Jun Rao and Ziji Yang V Acknowledgments In these four and a half years, I own my gratitude to so many people who help and support me en route to my Ph.D, as well as completing this dissertation. First I would like to thank my Ph.D. advisor Prof. Roberto Myers, for teaching me what is science, and his patience for putting up with my need-to-improve-a-lot writing skills. His dedication to science and pursuing the perfection impresses me all the time. I would also like to thank Prof. Siddarth Rajan, for being on my committee and mostly, for giving me so many insightful suggestions for my research projects along the way. I admire his kindness and bright mind of unlimited ideas. Prof. Wolfgang Windl, the most “fun” instructor I’ve ever known, led me experiencing the computing world when I took the computational class. I am grateful for the discussion with him regarding the GdN/GaN band alignment class project which led to a great collaboration. Also, I want to thank Prof. Suliman Dregia. I’ve learned so much materials science knowledge from his classes. He is always very helpful and offers great and long discussion regarding class, project and life. More importantly, I want to thank all my labmates. I can’t say enough how fortunate I am to work with those guys. They are the most friendly, supportive labmates I ever dreamed of working with and it’s like a big family for this group. For some nights, when I was staying up to write this thesis, some of them helped me editing it at the same time due the limited time I had. Santino Carnevale, the first labmate after me who joined VI the Myers group, is like a big brother to me. He is always there to help me out with MBE growth, class notes, draft proofreading, and explains the English idiom and expressions for me constantly. I have learned so much from him about the hardworking ethic and the organization skills. Thomas Kent, the most handy person I’ve met, has the best skills of putting things together such that the optical lab is very well equipped and maintained. I learned a lot from him regarding the scientific writing and hands-on skills. I would also like to thank Zihao Yang and ATM Golam Sarwar for many great discussions and suggestions on my thesis; Brandon Giles for his support for my English writing. The support from this group is one of the main reasons that I am getting close to the finish line. I will always be grateful. Also, this work could not have been done without the support of the MBE team: Digbijoy Nath, Sriram Krishnamoorthy from Dr. Rajan’s group whom I had learned so much from and shared great laughs with; Mark Brenner the staff member who maintains the system; Andrew Carlin, Chris Ratcliff, Krishna Swaminathan from Dr. Ringel’s group; formal postdoc Alessandro Giussani, Javier Grandal and Masihhur Laskar; along with the growers within the group (Santino, Thomas, Sarwar). This is the best team I ever worked with. I wish to keep the friendship with them for a lifetime. I would also like to thank my Chinese friends within the MSE and ECE department, Meng Tong, Siwei Cao, Lin Li, Lang Qin, Fan Yang, Yufeng Zheng, Rongpei Shi, Yipeng Gao, Zihao Yang, Yibin Gao, Zeng Zhang, Huimin Wang, Tengfei Jiang and more. Their support in academia and life got me through some difficult times. VII Finally, I would like to thank my boyfriend Andy. Without his love and cooking within the last couple of month, I can’t imagine how I would have survived the intense time of rushing to finish my PhD. I would like to thank my Aunt Gang and uncle Cipeng, without their encouragement and support; I would not apply for graduate school in United State at the first place. Also, I would like to thank my parents, my grandparents and my uncle Zihua back in China. Their love makes who I am today. VIII Vita 2008................................................................B.S. Optical Science and Engineering, Fudan University, Shanghai, China 2008................................................................Graduate student, Department of Electrical and Computer Engineering, Purdue University 2009 to present ..............................................Graduate Research Associate, Department of Material Science and Engineering, The Ohio State University 2011 ...............................................................Master of Science IX Publications 1. C. M. Jaworski, J. Yang, S. Mack, D. D. Awschalom, J. P. Heremans, R.C. Myers, “Observation of the Spin-Seebeck Effect in a Ferromagnetic Semiconductor”, Nature Materials 9, 898-903 (2010) 2. S. D. Carnevale, J. Yang, P.J. Phillips, M. J. Mills, R.C. Myers, “Three-Dimensional GaN/AlN nanowire heterostructures by separate nucleation and growth process,” Nano Letters 11, 866-871 (2011) 3. C. M. Jaworski, J. Yang, S. Mack, D. D. Awschalom, R.C. Myers, J. P. Heremans, “ Phonon spin distribution due to the Spin-Seebeck effect”, Phys. Rev. Lett. 106, 186601 (2011) 4. Z. Zhang, C. A. Hurni, A. R. Arehart, J. Yang, R. C. Myers, J. S. Speck, and S. A. Ringel, “Deep traps in nonpolar m-plane GaN grown by ammonia-based molecular beam epitaxy”, Appl. Phys. Lett. 100, 052114 (2012) 5. T. F. Kent, J. Yang, L. Yang, M. J. Mills, and R. C. Myers, “Epitaxial ferromagnetic nanoislands of cubic GdN in hexagonal GaN", Appl. Phys. lett. 100, 152111 (2012) 6. Sriram Krishnamoorthy , Thomas Kent, Jing Yang, Pil Sung Park, Roberto C. Myers, and Siddharth Rajan, "GdN Nanoisland-Based GaN Tunnel junctions", Nano Lett., 13, pp 2570–2575 (2013) X 7. J. Yang, F. Yang, T. F. Kent, M. J. Mills and R. C. Myers, “Semipolar InN/AlN multiple quantum wells on {10-1 5} faceted AlN on silicon”, Appl. Phys. lett. Submitted. 8. Jing Yang, Santino D. Carnevale, Roberto C. Myers,“Growth and structural characterization of AlN/GaN superlattice above decomposition temperature of GaN”, Journal of Vacuum Science and Technology B, submitted. Fields of Study Major Field: Materials Science and Engineering XI Table of Contents Abstract ............................................................................................................................... II Dedication .......................................................................................................................... V Acknowledgments............................................................................................................