Molecular Beam Epitaxial Growth, Characterization, and Nanophotonic Device Applications of InN Nanowires on Si Platform Songrui Zhao Department of Electrical and Computer Engineering Faculty of Engineering McGill University, Montreal April 2013 A thesis submitted to McGill University in partial fulfillment of the requirements of the degree of Doctor of Philosophy © Songrui Zhao 2013 To my wife, Rubing Table of Contents Acknowledgement ................................................................................................ vi Contribution of Authors .................................................................................... viii List of Figures ....................................................................................................... ix List of Acronyms ................................................................................................ xiii Abstract ............................................................................................................... xiv Abrégé .................................................................................................................. xv 1. Introduction ................................................................................................... 1-1 1.1. The importance of InN to the III-nitride family .................................... 1-2 1.1.1. The importance of InN to In(Ga)N-based devices: An example….. ............................................................................................ 1-3 1.2. Challenges in InN planar structures ....................................................... 1-4 1.2.1. Lack of intrinsic InN .................................................................. 1-4 1.2.1.1. The optical properties of nominally non-doped InN .... 1-5 1.2.1.2. The electrical transport properties of nominally non- doped InN ................................................................................... 1-7 1.2.2. Uncontrolled surface charge properties ..................................... 1-7 1.2.3. Difficulty in achieving p-type doped InN .................................. 1-9 1.2.4. The underlying mechanism of the challenges ............................ 1-9 1.2.4.1. Lack of suitable substrate ............................................ 1-9 1.2.4.2. The surface electron accumulation: The most debatable issue in InN ............................................................................... 1-11 1.3. The need of InN nanowire structures ................................................... 1-13 1.4. InN nanowires: The current status and challenges .............................. 1-13 1.4.1. The current status ..................................................................... 1-13 i 1.4.1.1. The poor optical and electrical properties of InN nanowires compared with InN planar structures ...................... 1-14 1.4.2. The challenges ......................................................................... 1-15 1.5. Summary of the contribution and the organization of this thesis ........ 1-16 2. Growth of InN, and other III-nitride nanowires ...................................... 2-18 2.1. Growth techniques of III-nitride nanowires ......................................... 2-18 2.2. Mechanisms of nanowire formation in general ................................... 2-18 2.2.1. The vapor-liquid-solid (VLS) mechanism ............................... 2-19 2.2.1.1. Recent progress of growing InN nanowires by the VLS mechanism ................................................................................ 2-20 2.2.2. The diffusion driven mechanism.............................................. 2-21 2.2.2.1. The spontaneous formation of III-nitride nanowires by molecular beam epitaxy ............................................................ 2-23 2.2.2.2. The spontaneous formation of InN nanowires by molecular beam epitaxy: The material quality challenge ......... 2-25 2.3. A novel approach by the in situ In seeding layer deposition technique ………………………………………………………………………..2-26 2.3.1. Demonstration of non-tapered InN nanowires ......................... 2-26 2.4. Growth of III-nitride nanowires on amorphous template .................... 2-28 2.4.1. Demonstration of high-quality GaN nanowires on SiOx with controlled orientation ........................................................................... 2-28 2.4.2. Growth of InN nanowires on SiOx .......................................... 2-33 2.4.3. Discussions .............................................................................. 2-34 2.5. The importance of III-nitrides grown by MBE to industrial applications.... .............................................................................................. 2-36 3. Characterization methods of InN, and other semiconductor nanowires and heterostructures ............................................................................................... 3-38 3.1. An overview ......................................................................................... 3-38 3.2. Optical characterization ....................................................................... 3-39 3.2.1. Advantage of optical characterization ...................................... 3-40 ii 3.2.2. X-ray photoelectron spectroscopy ........................................... 3-40 3.2.3. Photoluminescence spectroscopy ............................................. 3-44 3.2.4. Raman scattering spectroscopy ................................................ 3-48 3.3. Electrical characterization .................................................................... 3-50 3.3.1. Electrical transport of bulk semiconductors: The experimental approach and properties ....................................................................... 3-51 3.3.2. Electrical transport of semiconductor nanowires: The challenge, experimental approach, and properties ................................................ 3-52 3.3.3. Nanoprobing: A new technique to study the electrical transport properties of semiconductor nanowires ............................................... 3-54 4. Demonstration of intrinsic InN nanowires (I): Direct evidence from optical characterization and their optical properties ................................................ 4-55 4.1. The absence of surface electron accumulation on the grown non-polar surfaces ........................................................................................................ 4-55 4.2. Photoluminescence properties of intrinsic InN nanowires .................. 4-58 4.2.1. The narrow photoluminescence spectral linewidth and extremely low free carrier concentration .............................................................. 4-59 4.2.2. Near-band-edge recombination in intrinsic InN nanowires ..... 4-60 4.2.3. Phonon sideband emission ....................................................... 4-63 5. Demonstration of intrinsic InN nanowires (II): The electrical transport properties .......................................................................................................... 5-68 5.1. I-V characteristics ................................................................................ 5-68 5.2. The electrical transport properties derived using bulk geometry ........ 5-71 5.3. The electrical transport properties derived considering the large aspect ratio of nanowires ........................................................................................ 5-73 5.3.1. The formulae ............................................................................ 5-73 5.3.2. Free carrier concentration and electron mobility: Revised by considering the large aspect ratio of nanowires ................................... 5-74 6. Tuning the surface charge properties of InN nanowires ......................... 6-78 6.1. The presence of surface electron accumulation due to Si doping ........ 6-78 iii 6.2. Photoluminescence properties influenced by the presence of surface electron accumulation .................................................................................. 6-81 6.3. Discussions .......................................................................................... 6-84 6.3.1. The presence of two emission regions due to the presence of surface electron accumulation ............................................................. 6-84 6.3.2. The influence of surface electron accumulation on the phonon sideband emission ................................................................................ 6-89 6.3.3. Understanding the influence of the nanowire morphology on the surface charge properties ..................................................................... 6-90 7. The realization of p-type InN nanowires ................................................... 7-93 7.1. Evidence of the presence of Mg-acceptors in InN nanowires ............. 7-93 7.1.1. Photoluminescence properties of Mg-doped InN nanowires ... 7-94 7.2. Evidence of p-type surface in Mg-doped InN nanowires .................. 7-100 7.3. Direct evidence of p-type conduction measured by single nanowire field effect transistor .......................................................................................... 7-101 7.3.1. Discussions ............................................................................ 7-103 8. InN nanowire photodetectors ................................................................... 8-106 8.1. A brief introduction to photodetectors ............................................... 8-106 8.1.1. Photodetectors for