The fundamental atomic and electronic behaviour of clean silicon surfaces has been studied within a simple tight-binding picture of bonding in solids. Of the various contributions to the surface binding energy, the lowering in the promotion energy (i.e. rehybridization) which accompanies localized Jahn-Teller distortions has been identified as a major electronic driving force underlying the stability of silicon surfaces. The structure of Si(113) has been experimentally determined by the technique of scanning tunnelling microscopy (STM). Despite its high index, the Si(113) surface is found to be highly stable. STM images of both empty and filled states provide strong evidence for a particular structural model with a 3x2 unit cell. The STM results are explained in terms of a general rehybridization principle, suggested by the earlier theoretical study, which accounts for the low surface energy as well as the observed spatial distribution of empty and filled states. In addition, the STM images reveal a high density of domain boundaries which introduce energy states that pin the Fermi level and explain earlier reports of a 3x1 reconstruction for this surface. Voltage-dependent STM image simulations for the Si(113)3x2 surface have been carried out using a simple tight-binding description of surface electronic structure. Quantitative agreement with experiment is obtained confirming the qualitative rehybridization arguments used previously. The local barrier for tunnelling electrons is shown to have an important effect on the interpretation of STM images. The high stability of clean Si(l 13) is shown by STM to be disrupted by adsorption of submonolayer amounts of atomic hydrogen which saturates dangling bonds. Mass transport of silicon occurs and structural models are proposed for the resultant mixed 2x2 and 2x3 surface.

ATLAS is a multi-purpose detector for the LHC and will detect proton-proton collisions with center of mass energy of 14 TeV. Part of the central inner detector, the Semi-Conductor Tracker (SCT) barrels, were assembled and tested at Oxford University and later integrated at CERN with the TRT (Transition Radiation Tracker) barrel. The barrel SCT is composed of 4 layers of silicon strip modules with two sensor layers with 80 micro m channel width. The design of the modules and the barrels has been optimized for low radiation length while maintaining mechanical stability, bringing services to the detector, and ensuring a cold and dry environment. The high granularity, high detector efficiency and low noise occupancy (< 5*10^-4) of the SCT will enable ATLAS to have an efficient pattern recognition capability. Due to the binary nature of the SCT read-out, a stable read-out system and the calibration system is of critical importance. SctRodDaq is the online software framework for the calibration and also the physics running of the SCT and has been developed and tested during construction and commissioning of the detector with cosmics. It reliably measures the SCT performance parameters for each of the 6.3*10^6 channels in the SCT, identifies defects and problematic modules and writes them to an offline database for access from Athena, the ATLAS offline software framework. This dataflow chain has been exercised during the cosmics run at CERN, where a 5*10^5 cosmics sample for the combined SCT and TRT detectors was collected with a scintillator based trigger. It is now being commissioned in the ATLAS pit.

This thesis consists of a study of several thin film semiconductor structures of practical technological use either presently or in the near future. The first system studied is an ultra thin film single crystal gallium arsenide layer. The absorption spectra of these layers are measured and transitions at both the F- point and L-point of the Brillouin Zone are observed, the latter are not normally measurable in thicker layers. The observed shift in the F-point absorption edge is attributed to contributions from the Franz-Keldysh Effect and the Moss-Burstein Effect. The temperature dependence of the L-point energy gap is measured and compared with previous data. The next system investigated is an n-type porous silicon layer coated with p-type polyaniline. Both photoluminescence and electroluminescence spectra and the electrical characteristics have been measured for this system. The interface between the two layers is found to be a rectifying junction consistent with a potential barrier formed at the interface. In forward bias, it is possible to generate electroluminescence in the visible and near infra red regions. The final structure studied is a thin film cadmium sulphide-cadmium telluride solar cell structure. The cells are found to have a low efficiency of around 1% as grown, but a process of treatment with cadmium chloride and annealing in air improves this by a factor of approximately ten. Photoluminescence measurements on the back surface of the cadmium telluride revealed three major emission bands at 1.59 eV, 1.55 eV and 1.45 eV. By varying temperature and incident laser power, attempts at assigning the bands to specific impurity centres in the cadmium telluride is made Using a novel bevelling etch technique to prepare samples, depth dependent measurement of the photoluminescence is possible. This reveals that the major changes associated with the improvement in efficiencies occurs at the interface between the CdS and the CdTe.

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The objective of the proposed research is to analyze the effects of total ionizing dose (TID) on highly scaled CMOS and Silicon-Germanium Heterojunction Bipolar Transistors (SiGE HBTs). TID damage is caused by a build-up of charge at sensitive Si-SiO₂ interfaces and may cause device or circuit failure. TID damage is due to an accumulation of radiation particle strikes seen in extreme environments, such as space.

A new approach is discussed for the generation of high purity silicon from silica fume (SF), which is a waste by-product from the manufacture of metallurgical grade silicon. Process steps were developed and optimized including purification of SF, reduction by magnesium, and post-reduction leaching. Reduction was carried out successfully with initial HCl leached SF in a sealed chamber with varying Mg/SF ratios, temperature and time. These variables affected the production of silicon from SF. Suitable reduction conditions were found to be within the temperature range 750-850C and at approximately 2:1 ratio of Mg/SF. Reduction products were treated using a three-stage acid leaching. XRD, QXRD and ICP analyses of the final silicon powder product indicated that silicon with low impurity levels (low boron content) can be produced. Therefore, silicon produced by magnesiothermic reduction can be an attractive source for the production of solar grade silicon.

A new approach is discussed for the generation of high purity silicon from silica fume (SF), which is a waste by-product from the manufacture of metallurgical grade silicon. Process steps were developed and optimized including purification of SF, reduction by magnesium, and post-reduction leaching. Reduction was carried out successfully with initial HCl leached SF in a sealed chamber with varying Mg/SF ratios, temperature and time. These variables affected the production of silicon from SF. Suitable reduction conditions were found to be within the temperature range 750-850C and at approximately 2:1 ratio of Mg/SF. Reduction products were treated using a three-stage acid leaching. XRD, QXRD and ICP analyses of the final silicon powder product indicated that silicon with low impurity levels (low boron content) can be produced. Therefore, silicon produced by magnesiothermic reduction can be an attractive source for the production of solar grade silicon.

No description available.

The field of plasmonics has offered the promise to combine electronics and photonics at the nanometer scale for ultrafast information processing speeds and compact integration of devices. Various plasmonic waveguide schemes were proposed with the potential to achieve switching functionalities and densely integrated circuits using optical signals instead of electrons. Among these, the hybrid plasmonic waveguide stands out thanks to two sought-out properties: long propagation lengths and strong modal confinement. In this work, hybrid plasmonic waveguides and passive devices were theoretically investigated and experimentally demonstrated on an integrated silicon platform. A thin SiO2 gap between a gold conductive layer and a silicon core provides subwavelength confinement of light inside the gap. A long propagation length of 40µm was experimentally measured. A system of taper coupler connects the plasmonic waveguide to conventional photonic waveguides at a high efficiency of 80%. Passive devices were also fabricated and characterized, including S-bends and Y-splitters. / Microsystems and Nanodevices