In the past several years, epitaxial graphene on silicon carbide has been transformed from an academic curiosity of social scientists to a leading candidate material to replace silicon in post-CMOS electronics. This has come with rapid development of growth technologies, improved understanding of epitaxial graphene on the polar faces of silicon carbide, and new device fabrication techniques. The contributions of this thesis include refinement and improved understanding of graphene growth on the silicon- and carbon-faces in the context of managed local silicon partial pressure, high-throughput epitaxial graphene thickness measurement and uniformity characterization by ellipsometry, observations of nearly ideal graphene band structures on rotationally stacked carbon-face multilayer epitaxial graphene, presentation of initial experiments on localized in situ chemical modification of epitaxial graphene for an alternate path to semiconducting behavior, and novel device fabrication methods to exploit the crystal structure of the silicon carbide substrate. The latter is a particularly exciting foray into three dimensional patterning of the substrate that may eliminate the critical problem of edge roughness in graphene nanoribbons.

<p>Silicon carbide rectifiers are commercially available since 2001, and MESFET switches are expected to enter the market within a year. Moreover, three inch SiC wafers can be purchased nowadays without critical defects for the device performance and four inch substrate wafers are announced for the year 2005. Despite this tremendous development in SiC technology, the reliability issues like device degradation or high channel mobility still remain to be solved.</p><p>This thesis focuses on SiC surface passivation and termination, a topic which is very important for the utilisation of the full potential of this semiconductor. Three dielectrics with high dielectric constants, Al2O3, AlN and TiO2, were deposited on SiC with different techniques. The structural and electrical properties of the dielectrics were measured and the best insulating layers were then deposited on fully processed and well characterised 1.2 kV 4H SiC PiN diodes. For the best Al2O3 layers, the leakage current was reduced to half its value and the breakdown voltage was extended by 0.5 kV, reaching 1.6 kV, compared to non passivated devices.</p><p>As important as the proper choice of dielectric material is a proper surface preparation prior to deposition of the insulator. In the thesis two surface treatments were tested, a standard HF termination used in silicon technology and an exposure to UV light from a mercury lamp. The second technique is highly interesting since a substantial improvement was observed when UV light was used prior to the dielectric deposition. Moreover, UV light stabilized the surface and reduced the leakage current by a factor of 100 for SiC devices after 10 Mrad γ ray exposition. The experiments indicate also that the measured leakage currents of the order of pA are dominated by surface leakage.</p>

ETH, Diss.--Zürich, 2007.

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 57-58).

Thesis (M.S.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2010. / Committee Chair: Orlando, Thomas; Committee Member: El-Sayed, Mostafa; Committee Member: First, Phillip; Committee Member: Lackey, Jack; Committee Member: Tolbert, Laren. Part of the SMARTech Electronic Thesis and Dissertation Collection.

The properties of free-standing cubic silicon carbide for optoelectronic applications are explored in this work. The main focus of the work is on boron doped cubic silicon carbide, which is proposed as a highly useful material in several optoelectronic applications. The material is grown using sublimation epitaxy and the doped material is grown homoepitaxially on nominally undoped seeds. It is characterized using the experimental setups of photoluminescence spectroscopy, Nomarski interference spectroscopy and absorption spectroscopy. I have studied seed growth of nominally undoped cubic material on hexagonal (4H) substrates, and the influence on the grown material from the different faces of the substrate. It is found that it is not possible under the explored conditions to completely cover the growth area with the cubic polytype on the carbon face, but it can be done reproducibly on the silicon face. Reasons for this are discussed. Different doping setups are also explored. The influence on the material properties from growth conditions is explored. It is shown from absorption measurements that it is possible to grow boron doped cubic silicon carbide using this growth method, whereas optical microscopy studies show that the sample quality degrades with high doping concentrations. I have explored the luminescence properties of the material. No boron related emission is found with either room temperature or low temperature photoluminescence spectroscopy. Reasons for this are discussed using results from absorption measurements and optical microscopy.

published_or_final_version / Physics / Master / Master of Philosophy

No description available.

The mechanical responses of the comminuted ceramic under impact is important in understanding penetration resistance of the target, modeling the penetration process, developing ceramic models and designing better armor systems. To determine the dynamic compressive responses of ceramic rubbles, a novel loading/reloading feature in SHPB experiments was developed to produce two consecutive loading pulses in a single dynamic experiment with two strikers and two shapers. The first pulse pulverizes the intact specimen into rubble after characterizing the intact material. After unloading of the first pulse, a second pulse loads the comminuted specimen and gives the dynamic constitutive behavior of the rubble.With this new experimental technique, several series of experiments were conducted on an oxide ceramic -- alumina AD995 and a non-oxide ceramic--hot pressed silicon carbide, SiC-N, with different strain rates, various volume dilatations and damaged levels under 26 MPa, 56 MPa and 104 MPa confinement. The results show that the strength of the damaged ceramic is not very sensitive to strain rates within this research range and the pulse separation once the damage attains a critical level. When slightly damaged far below a critical level, the specimen remains nearly elastic; when transitionally damaged, the specimen strength gradually decrease from the slight damage level to the heavy damage level. Increasing confinement increases the strength of the ceramics. The crack patterns were dominantly axial splitting for the slight damage, axial splitting and fragmentation for the intermediate damage, and fragmentation and comminution for the heavy damage. For SiC-N, the volume dilatation history shows a delayed failure. SEM observations indicated that microstructural failure mechanism is intergranular fracture for alumina and transgranular fracture for SiC-N.Mohr-Coulomb criterion was successfully employed to describe the damaged ceramic and the parameters were determined. JH-1 model was employed to describe the failed SiC-N in the linearly segmentation description of the strength and the parameters were also determined. Through the analysis of JH-1 model for SiC-N, the critical damage level can be taken as D = 1.0. JH-2 model was used to describe analytically the damaged AD995 and the parameters were obtained. The critical damage value is 0.88 for alumina determined directly from JH-2 model. The description of JH-1 model is equivalent to Mohr-Coulomb criterion while it is unsuitable for JH-2 model due to the non-linear description. Based on the analysis of existing models and current experimental data, an empirical constitutive material model was developed for the damaged ceramic, which well described the completely damaged ceramic, but was unable to model the partially damaged ceramic.