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Physical Properties of Indium Nitride: a Highly Cation-Anion Mismatched Compound

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Physical Properties of Indium Nitride: a Highly Cation-Anion Mismatched Compound Physical properties of indium nitride: a highly cation-anion mismatched compound by Louis Frederick John Piper Thesis Submitted to the University of Warwick for the degree of Doctor of Philosophy Department of Physics May 2006 Contents Acknowledgements vii Declarations viii Abstract xii Abbreviations xiii Chapter 1 Introduction 1 1.1 Motivation for the thesis . 1 1.2 Organisation of the thesis . 3 1.3 Electronic properties of a semiconductor . 4 1.3.1 De¯nition of a semiconductor . 4 1.3.2 Various semiconductors . 5 1.3.3 Band structure approximations . 6 1.3.4 Carrier statistics . 10 1.4 Semiconductor interfaces . 11 1.4.1 Early studies of Schottky contacts . 11 1.4.2 Fermi level pinning . 13 1.4.3 Semiconductor free surfaces . 19 1.5 Space-charge calculations of free surfaces . 20 1.6 Summary . 23 Chapter 2 Experimental 25 2.1 Semiconductor surface spectroscopies . 25 2.2 Introduction to XPS . 25 2.3 Features typical of an XPS spectrum . 26 2.3.1 Background . 27 2.3.2 Core-level peaks . 28 2.3.3 Valence bands . 29 iii CONTENTS iv 2.4 Introduction to HREELS . 31 2.5 Semi-classical dielectric theory . 35 2.5.1 Program outline of HREELS of multilayers . 35 2.5.2 Evaluating the classical-loss probability for HREELS . 36 2.5.3 Dielectric functions and collective excitations . 37 2.5.4 HREEL simulations and Poisson-MTFA . 39 2.6 InN samples . 39 2.7 Atomic hydrogen sources . 42 Chapter 3 Indium arsenide 43 3.1 Surface preparation of indium arsenide . 43 3.1.1 Introduction . 43 3.1.2 Experimental details . 45 3.1.3 Core-level spectra . 45 3.1.4 Valence band spectrum . 47 3.1.5 Conclusion . 50 3.2 Space-charge pro¯les of indium arsenide . 50 3.2.1 Introduction . 50 3.3 Experimental details . 51 3.4 HREEL spectra . 52 3.5 Analysis . 54 3.5.1 InAs(100)-(4 2) . 56 £ 3.5.2 InAs(110)-(1 1) . 57 £ 3.6 Discussion . 59 3.7 Conclusion . 63 Chapter 4 Indium nitride: surface preparation 64 4.1 Introduction . 64 4.2 Experimental details . 65 4.3 XPS spectra . 66 4.4 Angular dependence . 68 4.5 HREELS . 70 4.6 Conclusion . 71 CONTENTS v Chapter 5 Indium nitride: valence band structure 72 5.1 Introduction . 72 5.2 Experimental details . 73 5.3 Experimental results . 74 5.4 Comparisons with theoretical calculations . 78 5.5 Conclusions . 80 Chapter 6 Indium nitride: origin of the electron accumulation 81 6.1 Introduction . 81 6.2 Experimental studies of clean InN surfaces . 82 6.2.1 Experimental details . 82 6.2.2 HREEL Spectra . 83 6.2.3 Space-charge calculations . 84 6.2.4 Discussion . 88 6.3 Ab initio calculations of the electronic structure of InN . 91 6.4 Origin of the electron accumulation . 93 6.4.1 Chemical trends of III-V semiconductors . 93 6.4.2 Surface state density of InN . 93 6.4.3 Physical nature of the surface states . 94 6.4.4 Conclusion . 95 Chapter 7 Indium nitride: Fermi level stabilisation by low energy ion bombardment 96 7.1 Introduction . 96 7.2 Experimental details . 97 7.3 Results . 97 7.4 Analysis . 99 7.5 Conclusion . 101 Chapter 8 Indium nitride: origin of the high unintentional n-type conduc- tivity 102 8.1 Introduction . 102 8.2 Experimental Details . 103 CONTENTS vi 8.3 Results . 104 8.4 Discussion . 104 8.5 Conclusion . 109 Chapter 9 Indium nitride: electron tunnelling spectroscopy of quantized states 110 9.1 Introduction . 110 9.1.1 Electron tunnelling spectroscopy . 110 9.1.2 Calculations of surface-bound quantized states . 113 9.2 Experimental details . 116 9.3 Experimental results . 117 9.4 Analysis . 119 9.5 Conclusion . 122 Chapter 10 Epilogue 123 10.1 Importance of the branch-point energy . 123 10.2 Indium nitride: a highly mismatched compound . 124 Appendix A EMRS Fall meeting 2005: the current status of InN 127 Appendix B Fermi level pinning at oxidized InN surfaces 132 Appendix C E®ects of the inhomogeneous electron distribution of InN 137 Bibliography 140 Acknowledgements I would ¯rst like to thank my supervisor. I have to thank Professor Chris McConville for providing three fantastic opportunities. Firstly, he helped to organise my ¯rst summer placement at QinetiQ Ltd. Malvern; where, under the guidance of Dr. Harvey Hardaway and Dr. Tim Ashley, my interest in semiconductors began. Secondly, Chris is thanked for welcoming me into his group at the University of Warwick. I was fortunate enough to work with Dr. Tim Veal, Dr. Imran Mahboob, and Paul Je®erson. I would especially like to thank Tim for his guidance, encouragement and friendship. In retrospect, it was the excited conversations with Tim, Imran and Paul during our extended tea breaks that I enjoyed (and shall miss) the most. I would like to thank Rob Johnston for his technical help with the HREELS chamber, and Drs Danny Law and Graham Beamson for maintaining an excellent XPS facility at Daresbury. Drs Bill Scha® and Hai Lu are thanked for providing the InN samples from Cornell University, and Professor Yasushi Nanishi and Dr. Hiroyuki Naoi are also acknowledged for their high-quality samples from Ritsumeikan University. Bill is further thanked for continued interest in our group's work. For their theoretical calculations and fruitful discussions, I would also like to thank Professor Friedhelm Bechstedt and Frank Fuchs. Thirdly, Chris has allowed me to proceed at my own pace throughout my Ph.D. and has encouraged me to publish and present my work. As a result of this approach, I have learnt valuable skills for the future, such as; writing papers; responding to referees' reports; writing grant applications to facilities and research groups; and presenting my work at national and international conferences. I would like to thank Tim once again for his help in honing these skills. At this point I would like to thank my parents and my sisters for their love, friend- ship, encouragement and help. I would also like thank my friends and house-mate for putting up with me during the last two and a half years. Last but not least, I would like to thank my ¯anc¶ee, Rebecca, for listening to me when I had work on my mind and for helping with the proof-checking of this thesis. vii Declarations I declare that this thesis contains an account of my research carried out in the Department of Physics at the University of Warwick between October 2003 and May 2006, under the supervision of Professor C. F. McConville. This research reported here has not been submitted, either wholly or in part, in this or any other academic institution for admission to a higher degree. The low-energy electron-di®raction (LEED) data from the InAs(100)-(4 2) and £ InAs(110)-(1 1) surfaces, along with the high resolution electron energy-loss (HREEL) £ spectra from the InAs(110)-(1 1) surface, reported in section 3.3 were taken by Dr. T. D. £ Veal (University of Warwick). The HREEL spectra from the InAs(100)-(4 2) surface was £ recorded by Dr. M. J. Lowe (University of Warwick). The X-ray photoemission spectra reported in section 4.4 were from measurements taken by Marc Walker (University of War- wick). The scanning electron microscopy in sections 3.2 and 5.4 was performed by Steve York and the atomic force microscopy mentioned in section 5.4 by Dr. N. R. Wilson (both, University of Warwick). The density functional theory calculations of InN in sections 5.5 and 6.4 were performed by Prof. Dr. F. Bechstedt, Frank Fuchs, and Prof. Dr. FurthmullerÄ (Friedrich-Schiller-UniversitÄat, Jena, Germany). The HREEL spectra in section 7.4 was measured by Dr. T. D. Veal and Dr. I. Mahboob (University of Warwick). The Hall mea- surements displayed in section 8.4 were from measurements made by Dr. W. J. Scha® and Dr. H. Lu (Cornell University, Ithaca, USA). The scanning tunnelling microscopy images and I-V spectra reported in section 9.4 were from measurements by Dr. M. H. Zareie and Dr. M. R. Philips (University of Technology, Sydney, Australia). All of the remain- ing data was obtained by the author. The data ¯tting, simulations, data analysis, and interpretation pertaining to these data was.
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