TWO-DIMENSIONAL ELECTRON TRANSPORT IN GALLIUM NITRIDE AND GALLIUM ARSENIDE-BASED HETEROSTRUCTURES by Hailing Cheng A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Physics) in the University of Michigan 2011 Doctoral Committee: Associate Professor Ҫagliyan Kurdak, Chair Professor Roy Clarke Professor Luming Duan Professor Rachel S. Goldman Professor Ctirad Uher Hailing Cheng 2011 All Rights Reserved ACKNOWLEDGEMENTS When I came to the University of Michigan, I never thought I would graduate as an experimentalist. My first deep thanks go to my advisor, Ҫagliyan Kurdak, who coached me and hammered me into a qualified experimentalist. I remember few years ago a cold leak happened in our He3 Dewar and we needed to ship it for fixing. While I worried about the container to box it, Ҫagliyan showed me what an experimentalist could do. He took me to a local Home-Depot and bought wooden pieces and a lot of carpenter tools. In an afternoon, we worked as carpenters and made a beautiful container. At that moment, I had a strong feeling about what an experimentalist meant. Those days really fly and I miss my time in U of M so much, not to mention the Michigan football games and March meetings. Those are my golden days and it would never come back again. In this limited space here, I would say my thanks to all the people I need to thank, though this list would never be complete. Many thanks go to my committees: Prof. Roy Clarke, Luming Duan, Rachel S. Goldman and Ctirad Uher, for their always support. Special goes to Roy for allowing me to stay in his lab to learn MBE, to Ctirad for allowing me to steal his liquid helium, to Rachel for beautiful GaAs samples, and to Prof. Morkoc for high quality GaN samples. I also need to thank Nadine for hosting my farewell party, Yu Jin for the collaborations, Vladimir for his talking in the midnight, Yan and Nan for their always-be-there-for-me. Again I need to thank Elizabeth, Richard and Steven for dissertation proofreading and lab supports, and finally I need to thank my family for reasons no need to mention. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS ............................................................................. ii LIST OF FIGURES ......................................................................................... vi LIST OF APPENDICES ................................................................................ xii ABSTRACT .................................................................................................... xiii CHAPTER 1. INTRODUCTION................................................................................... 1 1.1 Overview ..................................................................................................... 1 1.2 Heterostructures with a Two-Dimensional Electron Gas ........................... 2 1.3 Changing the 2DEG carrier density ............................................................ 7 1.4 Magnetotransport measurement on Hall bar samples ................................. 8 1.5 Van der Pauw method ............................................................................... 10 1.6 AlGaN/AlN/GaN heterostructures ............................................................ 12 1.7 InAlN/GaN heterostructures ..................................................................... 13 1.8 Dissertation Objectives ............................................................................. 15 1.9 Dissertation outline ................................................................................... 16 2. MAGNETOTRANSPORT MEASUREMENTS IN AlGaN/AlN/GaN HETEROSTRUCTURES ........................................................................ 19 2.1 Landau Level ............................................................................................ 19 2.2 Magneto transport measurements and Shubnikov-de Hass Effect ............ 22 2.3 AlGaN/InN/GaN sample growth .............................................................. 23 2.4 Sample Characterization ........................................................................... 25 3. TWO SUBBANDS CONDUCTION IN A GATED HIGH DENSITY InAlN/AlN/GaN HETEROSTRUCTURE .............................................. 29 3.1 InAlN/GaN sample growth ....................................................................... 29 iii 3.2 Magnetotransport measurements .............................................................. 31 3.3 Two conduction subbands with high mobility .......................................... 34 3.4 Charge distribution in two conductive subbands ...................................... 36 3.5 Summary and future directions ................................................................. 42 4. MAGNETOTRANSPORT MEASUREMENTS IN AlGaN/AlN/GaN 2DEGs WITH PARASITIC CHANNEL ................................................ 44 4.1 AlxGa1−xN/AlN/GaN heterostructures grown on epitaxial lateral overgrown GaN templates................................................................................................. 44 4.2 Magnetotransport measurements in AlGaN/AlN/GaN control samples ... 51 4.3 Magnetotransport measurements in SiN-GaN samples ............................ 55 4.4 Modeling of contact resistances in Hall bar samples ................................ 61 4.5 Magnetotransport measurements in ELO-GaN samples ........................... 67 4.6 Summary ................................................................................................... 70 5. SPIN-ORBIT INTERACTION IN GaN HETEROSTRUCTURES 72 5.1 Spin-Orbit Interaction in Semiconductors ................................................ 72 5.2 Spin-Orbit Coupling in AlGaN/GaN heterostructures .............................. 73 5.3 Weak Antilocalization measurements in AlGaN/GaN heterostructures ... 75 5.4 Spin-splitting energy in AlGaN/GaN heterostructures ............................. 78 5.5 Phase Coherence in AlGaN/GaN heterostructures ................................... 81 5.6 Spin-Orbit Coupling in InAlN/GaN heterostructures ............................... 83 5.7 InAlN/GaN heterostructures samples ....................................................... 85 5.8 WAL measurements for InAlN/GaN heterostructures samples ................ 89 5.9 SO field and Spin-Splitting energy in InAlN/GaN heterostructures ......... 91 5.10 SO parameters from SdH oscillations ..................................................... 95 5.11 Conclusion .............................................................................................. 98 6.ENERGY RELAXATION MEASURED BY WEAK ANTILOCALIZATION IN AlGaN/GaN HETEROSTRUCTRES ... 100 6.1 Electron-Phonon Interaction in AlGaN/GaN Heterostructures ............... 100 6.2 AlGaN/GaN Heterostructures samples ................................................... 101 6.3 Characterization of AlGaN/GaN Heterostructures Samples ................... 101 6.4 Weak antilocalization measurements ...................................................... 105 6.5 Power dissipation in AlGaN/GaN Heterostructures ............................... 109 6.6 Clean limit versus dirty limit .................................................................. 110 iv 6.7 Conclusion .............................................................................................. 115 7. OPERATION OF A SINGLE ELECTRON TRANSISTOR PLACED ON STACKED INTEGER QUANTUM HALL LAYERS AS A MAGNETOMETER ........................................................................... 116 7.1 AlGaAs/GaAs heterostructures and the quantum Hall effect ................. 116 7.2 Charge imbalance and long lived bulk currents ...................................... 117 7.3 Screening of additional magnetic field at high filling fractions .............. 122 7.4 Stacked quantum hall layers and single electron transistor sample ........ 124 7.5 Charge/ magnetic field ratio measured by the DC pulse and AC techniques ..................................................................................................... 131 7.6 The IQHL and SET composite device performs as a magnetometer ...... 134 7.7 Conclusion .............................................................................................. 137 8. CHARGE MOTIONS DETECTED BY SINGLE ELECTRON TRANSISTORS IN QUANTUM HALL LIQUID ............................... 138 8.1 Topological quantum computation and quantum Hall liquids ................ 138 8.2 The single electron transistors ................................................................ 140 8.3 Charge motion detected by a single electron transistor in multiple QHL .............................................................................................................. 141 8.4 Charge dynamics in normal and antidot QHL samples .......................... 150 8.5 Characterization of the FQHL sample and the SETs .............................. 154 8.6 Responses of QHL to the backgate voltage ............................................ 157 8.7 Responses of QHL to the magnetic pulse and the backgate voltage together ........................................................................................................ 162 8.8 Conclusions and future directions ........................................................... 172 9. SUMMARY AND SUGGESTIONS FOR FUTURE WORK ......... 174 9.1 Summary of present work ....................................................................... 174 9.2 Suggestions for future work .................................................................... 180 APPENDICES ..............................................................................................