by Ong Chung Wo. / Bibliography: leaves 118-120 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1986

by Pei-hsuon Chan. / Parallel title in Chinese characters. / Thesis (M.Ph.)--Chinese University of Hong Kong, 1988. / Bibliography: leaves 227-231.

by Ho Wai Hung. / Thesis (M.Ph.)--Chinese University of Hong Kong, 1988. / Bibliography: leaves 81-83.

Aluminum-silicon alloys are an important class of commercial non-ferrous alloys having wide ranging applications in the automotive and aerospace industries. Typical aluminum-silicon alloys have two major microstructural components, namely primary aluminum and an aluminum-silicon eutectic. While nucleation and growth of the primary aluminum in the form of dendrites have been well understood, the understanding of the evolution of the Al-Si eutectic is still incomplete. The microstructural changes caused by the addition of strontium to these alloys is another important phenomenon that still puzzles the scientific community. In this thesis, an effort has been made to understand the evolution of the Al-Si eutectic in the presence and absence of strontium through two sets of experiments: (1) Quench experiments, and (2) sessile drop experiments. The quench experiments were designed to freeze the evolution of the eutectic after various time intervals along the eutectic plateau. The sessile drop experiments were designed to study the role of surface energy in the formation of the eutectic in the presence and absence of strontium. Both experiments were conducted on high purity alloys. Using observations from these experiments, possible mechanis(s) for the evolution of the Al-Si eutectic and the effects of strontium on modifying the eutectic morphology are proposed.

No description available.

近年在矽光子學方面的研究日漸增多，主要原因是在高效能電腦，低成本通訊接取網絡及集成光學感應器等各方面有很大的潛在應用。以矽為原材料的各種光學器件已經被廣泛研究，包括電光調制器，光感應器和各式各樣主動及被動器件。但是由於矽是一種間接能隙的物質，即是由電子激發的電子電洞的結合是屬於非輻射躍遷，所以不可以得到光放大和激光器的效果。為了製作集成激光器，已經有很多不同的研究方案，例如在矽波導上摻雜鉺或是混合集成矽和-族半導體。在這篇論文中，我們提出並且論証了一個創新的方案去製作由光纖和矽波導混合而成的激光器，大大簡化了設計和生產過程。 / 在論文中，我們會集中討論選取光波長的器件及整體結構的設計。在首次的結構設計上，我們利用了分佈在矽波導兩側的布拉格反射鏡作為選取光波長的器件和一小段以鉺摻雜的光纖作為放大器。我們將會詳細形容該器件的設計、模擬效果和實驗結果。我們已經透過實驗証明了單波長的光纖－矽波導混合激光器，其側模抑制超過35分貝。 / 另一方面，為了製作多波長的光纖－矽波導混合激光器，我們利用微環諧震器來取代分佈在矽波導兩側的布拉格反射鏡作為選取光波長的器件。我們將會討論微環諧震器的設計以及達到穩定多波長的光纖和矽波導混合激光器的設計要求。 / Motivated by potential applications for optical interconnects in high performance computing, low cost optical access networks in telecommunications and integrated optical sensors, there has been much research in recent years on silicon photonics. Different silicon-based photonic devices have been studied, including optical modulators, detectors and various types of active and passive components. However, since the bandgap of silicon is indirect, the recombination of carriers injected by electrical pumping is dominated by non-radiative transitions and thus it is not possible to get optical gain via current injection into silicon diodes. / To implement integrated laser, different approaches such as erbium doping on silicon waveguide and hybrid integration of III-V semiconductors on silicon have been investigated. In this thesis, we propose and demonstrate a novel approach for making a hybrid fiber-silicon laser to simplify the design and fabrication processes. We propose the use of Erbium-doped fiber (EDF) to provide gain and silicon devices to provide all the other functionalities needed for a modulated laser. / The thesis focuses on the design of wavelength selective element and the structure of hybrid fiber-silicon laser. The first design includes a silicon waveguide side-cladding distributed Bragg reflector (WSC-DBR) as the wavelength selective component on silicon-on-insulator (SOI) wafer and a short length of EDF as the gain medium. The details of design, simulation and experimental results of the WSC-DBR will be described. Single wavelength WSC-DBR hybrid fiber-silicon laser is demonstrated with a side mode suppression ratio (SMSR) of over 35dB. / We also investigate the use of a micro-ring resonator to replace WSC-DBR for selecting multiple wavelengths. Details of the micro-ring resonator are given and we discuss the requirement and design criteria to achieve stable multi-wavelength lasing. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Fung, Ka Yan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Abstracts also in Chinese. / ABSTRACTOF THESIS ENTITLED: --- p.ii / ACKNOWLEDGEMENT --- p.v / TABLE OF CONTENT --- p.vii / Chapter 1 --- INTRODUCTION --- p.10 / Chapter 1.1 --- Photonic Integrated Circuits --- p.10 / Chapter 1.2 --- Silicon Photonics --- p.13 / Chapter 1.3 --- Lasers in Silicon --- p.20 / Chapter 1.4 --- Motivation --- p.27 / Chapter 1.5 --- References --- p.29 / Chapter 2 --- ERBIUM DOPED FIEBR AND FIBER LASERS --- p.34 / Chapter 2.1 --- Erbium doped fiber --- p.34 / Chapter 2.2 --- Multi-wavelength lasers --- p.45 / Chapter 2.3 --- References --- p.54 / Chapter 3 --- SINGLE CHANNEL HYBRID FIBER-SILICON LASER --- p.59 / Chapter 3.1 --- Introduction of Distributed Bragg reflector --- p.60 / Chapter 3.2 --- Design of waveguide side-cladding distributed Bragg reflector --- p.63 / Chapter 3.3 --- Simulation results of waveguide side-cladding distributed Bragg reflector --- p.66 / Chapter 3.4 --- Device fabrication --- p.69 / Chapter 3.5 --- Experimental results of waveguide side-cladding distributed Bragg reflector --- p.71 / Chapter 3.6 --- Experimental results of hybrid fiber-silicon laser --- p.77 / Chapter 3.7 --- Introduction of micro-ring resonator --- p.81 / Chapter 3.8 --- Design of race track micro-ring resonator --- p.85 / Chapter 3.9 --- Experimental results of race track micro-ring resonator --- p.88 / Chapter 3.10 --- Experimental results of hybrid fiber-silicon laser with ring resonator --- p.95 / Chapter 3.11 --- Summary --- p.99 / Chapter 3.12 --- References --- p.101 / Chapter 4 --- DUAL WAVELENGTH HYBRID FIBER SILICON LASER --- p.102 / Chapter 4.1 --- Design of micro-ring resonator for dual wavelength --- p.103 / Chapter 4.2 --- Experimental results of micro-ring resonator --- p.104 / Chapter 4.3 --- Experimental results of dual wavelength hybrid fiber-silicon laser --- p.108 / Chapter 4.4 --- Summary --- p.119 / Chapter 4.5 --- References --- p.121 / Chapter 5 --- DUAL WAVELENGTH VERTICAL GRATING COUPLER --- p.123 / Chapter 5.1 --- Introduction of grating coupler --- p.123 / Chapter 5.2 --- Design of dual wavelength vertical grating coupler --- p.125 / Chapter 5.3 --- Simulation of dual wavelength vertical grating coupler --- p.127 / Chapter 5.4 --- Experimental results of dual wavelength vertical grating coupler --- p.135 / Chapter 5.5 --- Summary --- p.138 / Chapter 5.6 --- References --- p.139 / Chapter 6 --- CONCLUSION AND FUTURE WORK --- p.141 / Chapter 6.1 --- Conclusion --- p.141 / Chapter 6.2 --- Future work --- p.144 / Chapter 6.3 --- References --- p.146 / Chapter APPENDIX A: --- PUBLICATION LIST --- p.147 / Chapter APPENDIX B: --- LIST OF TABLES --- p.149 / Chapter APPENDIX C: --- LIST OF FIGURES --- p.150 / Chapter APPENDIX D: --- METHODS OF LINEWIDTH MEASUREMENT --- p.155 / Chapter APPENDIX E: --- EQUIPMENT INFORMATION --- p.164

This dissertation explores the electronic characteristics of silicon at the single molecule level. This idea is born as we enter the post-Moore’s law era when the exponential shrinking of conventional silicon microelectronics has begun to stall and an investigation of molecular materials is timely. Single-molecule electronic components have shown promising functionalities such as conductors, switches, and diodes, and single molecule junctions have become a widely used test-bed for probing electron transport properties at the molecular level. In this thesis, we use scanning tunneling microscope break junction method to create single molecule junctions with a variety of silicon molecular wires. Our results demonstrate electronic properties of silicon beyond it being a semiconductor in its bulk form. We begin this work in pursuit of an expanded understanding of low-k dielectric components with an experimental goal on determining the cause of its breakdown. Low-k dielectrics are beneficial as they enable faster switching speeds and lower heat dissipation, however, they tend to breakdown after prolonged usage under an applied voltage. At the atomic level, low-k dielectric breakdown involves bond rupture. To determine which bond breaks easily, we conduct experimental studies on the robustness of individual chemical bonds that are commonly found in low-k dielectrics. We subject the single molecule junctions to a high bias and investigate the breakdown phenomenon of individual Si-Si, Ge-Ge, Si-O, and Si-C bonds. Among these, Si-C proved to be significantly more durable than the others. To further prove our hypothesis that the Si-Si bond ruptures under the applied high bias, we design a two-path molecular structure consisting of a Si-Si bond in parallel with a naphthyl group. The broken junction shows conduction through the naphthyl pathway, strongly indicating that the Si-Si bond is breaking. This demonstrates a method for probing the bond cleavage under an electric field and provides insights to the weak links in low-k dielectrics. Next, we study the fundamental charge transport characteristics of single molecule junctions comprised of Si and Ge-based molecular wires, starting with the simplest form - linear atomic chains. We observe a slower decay of conductance with increasing length in the silanes and germanes than in alkanes, indicating that the electronic delocalization in the Si-Si and Ge-Ge -bonds is stronger than that of the well-studied C-C bonds. Furthermore, we demonstrate that this electronic delocalization in the Si-Si and Ge-Ge bonded backbones enables single-molecule conductance switching. This conductance switch, induced by a mechanical modulation, relies on the nature of the terminal groups and constitutes the first example of a stereoelectronic switch. We also study the molecular conductance of these silanes with metal contacts other than Au, which can potentially open up interesting avenues as metal varies in its electronic states and catalytic activities. We find that Ag electrodes enable higher conductance for thiol-terminated silanes than Au or Pt electrodes. The electrical properties of more complex silicon structures - silicon rings - were probed. We choose a five-membered silicon ring as a target system to investigate the effect of isomerism on single molecule conductance. We find that due to the flexibility of the ring, multiple conformations contribute to the spread in the measured conductance for each isomer. This provides us with a starting point to further compare the conductance of a variety of silicon rings. We find that most of the silicon rings are less conductive than their linear counterparts due to the suboptimal backbone conformation for electronic coupling. In particular, destructive quantum interference appears in one of the bicyclic structures and leads to an exceptionally low conductance. This is the first example of a destructive quantum interference feature ever observed experimentally in a π-bonded rather than a σ-bonded system. Finally, we investigate the impact of strain on molecular conductance of silanes. In one case, we introduce the strain using a silacyclobutane ring in the backbone. Unexpectedly, we find that ring strain enables a new Au-silacycle binding mode, resulting in a much higher conductance state. In another molecular design, we choose disilaacenaphthene in the backbone. This strained disilane is found to constitute an example of a direct Si-to-Au contact in single molecule circuits, thereby demonstrating a new binding motif that is valuable for designing high conducting molecular components. Taken together, this body of work provides important knowledge about the transport properties of silicon at the nano-scale, as well as insights on the design of silicon components for nanoelectronics. This work represents one step forward to create functional silicon molecular components.

Hydrogenated amorphous silicon films subjected to KrF excimer laser irradiation with a profiled beam in air leads to the formation of microstructures. The main objective of this research was to perform a comprehensive study in understanding this material in three different aspects: thermal, electrical, and optical properties by experiment, SEM analysis and modelling. For the thermal interactions, analysis was carried out to investigate factors relating to the formation of the microstructures in a range of applied laser fluences from 93.8 to 443.8 mJ/cm2. The tallest microstructures were formed with average height from 1 to 3 ?m at laser fluence of 312.5 mJ/cm2. Investigation also include the effect of different applied laser fluence, different scanning schemes, the effect of the presence of 300 nm metal layer, and irradiation environment. Thermal modelling using COMSOL simulation software was used to simulate heat transfer during laser-material interaction and the results suggest a fair agreement with experimental findings. SEM and TEM reveal that the material formed was an oxynitride with embedded particles of crystalline silicon. In the electrical part, conductivity and field emission were the main tools to help elucidate the internal structure. Arrhenius plots acquired from conductivity measurements demonstrates a decrease in activation energy from 0.8957 eV from original sample to 0.3955 and 0.1727 eV for HE and LE sample respectively. Analysis also showed an agreement with Meyer Neldel rule for both samples. Observation made on the ratio of dark current to photogenerated current revealed the decrease from 59600 in original sample to 1.77 and 1.40 for HE and LE samples respectively. For the field emission properties, IE plots from samples were analysed using 170 ?m fixed gap structure, and lowest emission thresholds were achieved at 3 and 2.4 V/?m for HE and LE samples respectively. The results were fitted to a model of conducting particles in an insulating matrix offering a transport route to the surface. In the optical part, FTIR measurements were carried and analysis in IR absorbance profile within range of 550 to 2200 cm-1 demonstrates SiHx absorbance peaks at 640 cm-1, between 1980 to 2100 cm-1, and at 2095 cm-1. Hydrogen content was found to be decreased with the increase in applied laser fluence from 12 % in original sample to 4.2 and 1.5 % for HE and LE sample respectively. Measurements using UV-Vis between wavelengths of 200 to 1100 nm shows high absorbance up to 98% for laser process sample from 218.8 to 312.5 mJ/cm2. TR analysis demonstrated increasing absorbance properties at increasing incident angle. Raman spectroscopy showed an increase in the crystal fraction with laser fluence. The final analysis work in this thesis examines the material as a potential disordered photonic crystal and studies the propagation and localisation of light in ordered and disordered photonic crystal, modelled using COMSOL simulation software. This shows the transition from diffusive to localised propagation. A number of applications are suggested for this structured material. This is the first report of a new large area ‘black silicon’ material that has a number of interesting applications.

Abstract not available

Modelling of phosphorus donor-based silicon (Si:P) qubit devices and mesoscopic single-electron devices is presented in this thesis. This theoretical analysis is motivated by the use of Si:P devices for scalable quantum computing. Modelling of Si:P single-electron devices (SEDs) using readily available simulation tools is presented. The mesoscopic properties of single and double island devices with source-drain leads is investigated through ion implantation simulation (using Crystal-TRIM), 3D capacitance extraction (FastCap) and single-electron circuit simulation (SIMON). Results from modelling two generations of single and double island Si:P devices are given, which are shown to accurately capture their charging behaviour. The trends extracted are used to forecast limits to the reduction in size of this Si:P architecture. Theoretical analysis of P2+:Si charge qubits is then presented. Calculations show large ranges for the SET measurement signal, Δq, and geometric ratio factor, α, are possible given the 'top-down' fabrication procedure. The charge qubit energy levels are calculated using the atomistic simulator NEMO 3-D coupled to TCAD calculations of the electrostatic potential distribution, further demonstrating the precise control required over the position of the donors. Theory has also been developed to simulate the microwave spectroscopy of P2+:Si charge qubits in a decohering environment using Floquet theory. This theory uses TCAD finite-volume modelling to incorporate realistic fields from actual device gate geometries. The theory is applied to a specific P2+:Si charge qubit device design to study the effects of fabrication variations on the measurement signal. The signal is shown to be a sensitive function of donor position. Design and analysis of two different spin qubit architectures concludes this thesis. The first uses a high-barrier Schottky contact, SET and an implanted P donor to create a double-well suitable for implementation as a qubit. The second architecture is a MOS device that combines an electron reservoir and SET into a single structure, formed from a locally depleted accumulation layer. The design parameters of both architectures are explored through capacitance modelling, TCAD simulation, tunnel barrier transmission and NEMO 3-D calculations. The results presented strengthen the viability of each architecture, and show a large Δq (> 0.1e) can be expected.