by Choy Wing Hong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 95-102). / Text in English; abstract also in Chinese. / by Choy Wing Hong. / ABSTRACT --- p.vi / ACKNOWLEDGEMENTS --- p.x / LIST OF FIGURES --- p.xi / LIST OF TABLES --- p.xiii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Surface passivation techniques --- p.2 / Chapter 1.2.1 --- Sulfide solution passivation --- p.2 / Chapter 1.2.2 --- Gas-phase sulfide passivation --- p.3 / Chapter 1.2.3 --- Ultra-violet and ozone exposure --- p.4 / Chapter 1.3 --- Surface structure of sulfide-passivated surface --- p.5 / Chapter 1.4 --- Surface structure of ultra-violet/ozone oxidation --- p.8 / Chapter 1.5 --- Objectives of present study --- p.10 / Chapter Chapter 2 --- Instrumentation --- p.12 / Chapter 2.1 --- Introduction --- p.12 / Chapter 2.2 --- Atomic force microscopy (AFM) --- p.12 / Chapter 2.2.1 --- The development of AFM --- p.12 / Chapter 2.2.2 --- Basic principles of AFM --- p.12 / Chapter 2.2.3 --- Forces and their relevance to atomic force microscopy --- p.13 / Chapter 2.2.3.1 --- Van Der Waals forces --- p.15 / Chapter 2.2.3.2 --- Repulsive forces --- p.15 / Chapter 2.2.3.3 --- Capillary forces --- p.15 / Chapter 2.2.4 --- Displacement sensor of AFM --- p.15 / Chapter 2.2.4.1 --- Electron tunneling --- p.16 / Chapter 2.2.4.2 --- Optical interference --- p.16 / Chapter 2.2.4.3 --- Laser beam deflection --- p.16 / Chapter 2.2.5 --- Instrument specification --- p.17 / Chapter 2.2.5.1 --- Contact mode AFM --- p.17 / Chapter 2.3 --- X-ray photoelectron spectroscopy --- p.19 / Chapter 2.3.1 --- The development of XPS --- p.19 / Chapter 2.3.2 --- Basic principles of XPS --- p.19 / Chapter 2.3.3 --- XPS experiments --- p.23 / Chapter 2.3.4 --- Quantitative analysis --- p.26 / Chapter 2.3.4.1 --- Atomic concentration of a homogenous materials --- p.26 / Chapter 2.3.4.2 --- Layer structure --- p.27 / Chapter 2.4 --- Rutherford backscattering spectrometry (RBS) --- p.29 / Chapter 2.4.1 --- Basic principles --- p.29 / Chapter 2.4.2 --- Kinematics --- p.29 / Chapter 2.4.3 --- Channeling --- p.31 / Chapter Chapter 3 --- Surface treatments --- p.32 / Chapter 3.1 --- Semiconductor wafer --- p.32 / Chapter 3.2 --- Cleaning procedures --- p.32 / Chapter 3.3 --- Polysulfide passivation --- p.34 / Chapter 3.4 --- UV/Ozone oxidation --- p.39 / Chapter Chapter 4 --- Surface roughness and oxide contents of sulfide passivation --- p.41 / Chapter 4.1 --- Introduction --- p.41 / Chapter 4.2 --- Experimental methodology --- p.42 / Chapter 4.3 --- Etching --- p.44 / Chapter 4.3.1 --- Etching effect of polysulfide solution --- p.45 / Chapter 4.3.2 --- Possible consequences of the etching effect --- p.45 / Chapter 4.4 --- Oxide contents --- p.47 / Chapter 4.4.1 --- Oxide gained during polysulfide solution treatment --- p.47 / Chapter 4.4.2 --- Oxide gained after polysulfide passivation --- p.47 / Chapter 4.5 --- Surface roughness --- p.49 / Chapter 4.5.1 --- Surface roughness after different passivation methods --- p.49 / Chapter 4.5.2 --- The sticking probability after different passivations --- p.51 / Chapter 4.6 --- The spiral ladder of solution-phase passivation --- p.55 / Chapter 4.7 --- Conclusions --- p.58 / Chapter Chapter 5 --- Sulfide on Ge/GaAs heterojunction --- p.59 / Chapter 5.1 --- Introduction --- p.59 / Chapter 5.1.1 --- Band structure of Ge/GaAs heteroj unction --- p.59 / Chapter 5.1.2 --- Lattice match of Ge/GaAs heteroj unction --- p.60 / Chapter 5.1.3 --- The growth of Ge on GaAs using molecular beam epitaxy --- p.62 / Chapter 5.2 --- The growth of Ge on GaAs using thermal pulse annealing --- p.63 / Chapter 5.3 --- Sulfide as an atomic interdiffusion barrier --- p.65 / Chapter 5.3.1 --- Experimental methodology --- p.65 / Chapter 5.3.2 --- Crystallinity of Ge --- p.67 / Chapter 5.3.3 --- Results and discussions --- p.67 / Chapter 5.3.3.1 --- RBS and XPS results --- p.67 / Chapter 5.3.3.2 --- AFM and I-V results --- p.71 / Chapter 5.4 --- Conclusions --- p.71 / Chapter Chapter 6 --- UV/03 on Ge/GaAs heterojunction --- p.72 / Chapter 6.1 --- Introduction of UV/o3 oxidation --- p.72 / Chapter 6.2 --- UV/o3 oxidation on GaAs --- p.74 / Chapter 6.3 --- Ge on UV/o3 treated GaAs --- p.76 / Chapter 6.3.1 --- Experimental methodology --- p.76 / Chapter 6.3.2 --- Crystallinity of Ge --- p.77 / Chapter 6.3.3 --- AFM results --- p.77 / Chapter 6.3.4 --- RBS results --- p.80 / Chapter 6.4 --- Diodes --- p.82 / Chapter 6.4.1 --- Fabrication of diode --- p.82 / Chapter 6.4.2 --- Diode characteristics --- p.84 / Chapter 6.4.3 --- I-V characteristics --- p.90 / Chapter 6.5 --- Conclusions --- p.90 / Chapter Chapter 7 --- Conclusion and future work --- p.93 / Chapter 7.1 --- Conclusions --- p.93 / Chapter 7.2 --- Future works --- p.94 / Reference --- p.95

M. Tech. Digital Technology. / This dissertation reports on an optical-based two-dimensional position sensor for use in Active Magnetic Bearings (AMB) to measure the position of the levitated rotor. The motivation for the deployment of optical technology is the well-known advantage of high precision contactless displacement measurement. The radial and axial edges of the rotor are illuminated by red and green laser beams respectively. The position of the rotor is determined from its image projected on a Charge Coupled Device (CCD) sensor. The measuring principle is demonstrated as a position sampler in the closed loop control of an active magnetic bearing model. The image representing the position is processed with a real-time algorithm on a Field Programmable Logic Gate Array. The principle of operation of a CCD as a position sensor is analysed in order to establish how the image captured by the CCD can be processed to determine the position of the rotor. A simple AMB is modelled in which the sensor acts as a feedback position device. The main objective of the model is to evaluate the accuracy of the system. The purpose of the overall sensing technique to be used is to achieve highly accurate and precise measurements with CCD-based optical metrology.

CuI is a p-type transparent conductive semiconductor with unique optoelectronic properties, including wide band gap (3.1 eV), high hole mobility (>40 cm2 V−1 s−1 in bulk), and large room-temperature exciton binding energy (62 meV). The difficulty in epitaxy of CuI is the main obstacle for its application in advanced solid-state electronic devices. Herein, room-temperature heteroepitaxial growth of CuI on various substrates with well-defined in-plane epitaxial relations is realized by reactive sputtering technique. In such heteroepitaxial growth the formation of rotation domains is observed and hereby systematically investigated in accordance with existing theoretical study of domain-epitaxy. The controllable epitaxy of CuI thin films allows for the combination of p-type CuI with suitable n-type semiconductors with the purpose to fabricate epitaxial thin film heterojunctions. Such heterostructures have superior properties to structures without or with weakly ordered in-plane orientation. The obtained epitaxial thin film heterojunction of p-CuI(111)/n-ZnO(00.1) exhibits a high rectification up to 2 × 109 (±2 V), a 100-fold improvement compared to diodes with disordered interfaces. Also a low saturation current density down to 5 × 10−9 Acm−2 is formed. These results prove the great potential of epitaxial CuI as a promising p-type optoelectronic material.