Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Cressler, John; Committee Member: Citrin, David; Committee Member: Shen, Shyh-Chiang. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Laskar, Joy; Committee Member: Cressler, John; Committee Member: Tentzeris, Manos. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M.S.)--Youngstown State University, 2009. / Includes bibliographical references (leaves 44-45). Also available via the World Wide Web in PDF format.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 67-69). Also available in electronic version. Access restricted to campus users.

To overcome the issues of mobility degradation and charge trapping in silicon high-κ MOSFET, a stacked Y₂O₃(top)/HfO2(bottom) gate dielectric on silicon substrate has been developed. Compared to the HfO₂ reference, the new dielectric shows similar scalability, but superior channel mobility and device reliability. The mobility improvement can be attributed to reduced remote phonon scattering, which is associated with the smaller ionic polarization of Y₂O₃, and the suppressed coulomb scattering due to less electron trapping in the bulk of high-κ layer, and reduced metal impurities in the substrate. The passivation mechanisms for the silicon IPL passivation technique in GaAs/[alpha]-Si IPL/high-κ MOS system have been investigated. We demonstrate the [alpha]-Si IPL thickness dependence and substrate type dependence of interface state density (Dit) for GaAs MOS capacitors. The interface state density is strongly correlated to the thickness and quality of un-oxidized Si IPL and its interaction with the underlying substrate. The results can be explained by the models related to the quantum well narrowing or the reduced local trap density as the unoxidized Si IPL layer thickness decreases. By using optimal Si IPL thickness (~10 Å), GaAs MOS devices can achieve the same interface quality, as its silicon counterpart. Using Si IPL to unpin the surface Fermi level, the selfaligned depletion-mode and enhancement-mode GaAs n-MOSFETs are demonstrated. In addition, the charge trapping and wear-out characteristics of the GaAs/Si IPL/HfO2/TaN MOS devices are systematically investigated. High performance In0.53Ga0.47As nMOSFETs with Si IPL and HfO2 gate oxide have been demonstrated. We systematically investigate the impacts of 1) Source/Drain activation temperature, 2) post deposition annealing (PDA) temperature, 3) In[subscrip 0.53]Ga[subscript 0.47]As channel doping concentration, 4) channel thickness and 5) Si IPL thickness on the transistor performances. With the [mu]m, V[subscript d]=50 mV), drive current of 158 mA/mm (L[subscript g]=5 [mu]m, V[subscript gs]=V[subscript th]+2 V, V[subscript d]=2.5 V), and the peak effective channel mobility of 1034 cm2/V-s. InP nMOSFETs with Si IPL and HfO₂ have been demonstrated. The effects of Si IPL on the transistor performances and reliability characteristics are investigated. It is found that even through InP is a forgiving channel material with respect to surface Fermi level pinning, applying silicon IPL still improves the transistor performance and reliability. But the choice of Si IPL is critical for device design. Both in-sufficient passivation and excessive Si IPL should be avoided. optimal combination of these impacting factors, excellent device characteristics have been obtained, including the peak transconductance of 7.7 mS/mm (Lg=5 μm, Vd=50 mV), drive current of 158 mA/mm (Lg=5 [mu]m, Vgs=Vth+2 V, Vd=2.5 V), and the peak effective channel mobility of 1034 cm2/V-s. InP nMOSFETs with Si IPL and HfO₂ have been demonstrated. The effects of Si IPL on the transistor performances and reliability characteristics are investigated. It is found that even through InP is a forgiving channel material with respect to surface Fermi level pinning, applying silicon IPL still improves the transistor performance and reliability. But the choice of Si IPL is critical for device design. Both in-sufficient passivation and excessive Si IPL should be avoided. / text

Controlling catalyst morphology and composition are required to make meaningful structure-activity/stability relationships for the design of future catalysts. Herein, we have employed strategies of presynthesis and infusion or electroless deposition to achieve exquisite control over catalyst composite morphology. The oxygen reduction (ORR) and the oxygen evolution reactions (OER) were chosen as model systems, as their slow kinetics is a major limiting factor preventing the commercialization of fuel cells and rechargeable metal air batteries. In acid, bimetallic (Pt-Cu, Pd-Pt) and monometallic (Pt) catalysts were presynthesized in the presence of capping ligands. Well alloyed Pt-Cu nanoparticles (3-5 nm) adsorbed on graphitic mesoporous carbon (GMC) displayed an ORR activity >4x that of commercial Pt. For both presynthesized Pt and Pt-Cu nanocrystals on GMC, no activity loss was also observed during degradation cycling due to strong metal-support interactions and the oxidation resistance of graphitic carbon. Similar strong metal-support interactions were achieved on non-graphitic carbon for Pd3Pt2 (<4 nm) nanoparticles due to disorder in the metal surface This led to enhanced mass activity 1.8x versus pure Pt, as well as improved stability. For basic electrolytes, we developed an electroless co-deposition scheme to deposit Ag (3 nm) next to MnOx nanodomains on carbon. We achieved a mass activity for Ag-MnOx/VC, 3x beyond the linear combination of pure component activities due to ensemble effects, where Ag and MnOx domains catalyze different ORR steps, and ligand effects from the unique electronic interaction at the Ag-MnOx interface. Activity synergy was also shown for Ag-Pd alloys (~5 nm), achieving up to 5x activity on a Pd basis, resulting from the unique alloy surface of single Pd atoms surrounded by Ag. Lastly, we combined arrested growth of amorphous nanoparticles with thin film freezing to create a high surface area, pure phase perovskite aggregate of nanoparticles after calcination. Sintering was mitigated during the high temperature calcination required to form the perovskite crystals. The high surface areas and phase purity led to OER mass activities ~2.5x higher than the benchmark IrO2 catalyst. / text

The sun is a vast source of renewable energy, which can potentially be used to satisfy the world's increasing energy demand. Yet many material challenges need to be overcome before solar energy conversion can be implemented on a larger scale. This dissertation focuses on materials used for solar energy conversion through photo-electrochemical (PEC) processes. It discusses methods for improving PEC materials, namely mixed metal oxide semiconductors, by nanostructuring, incorporation of additional elements, and application surface electrocatalysts. In this dissertation several material synthesis techniques are detailed. A high vacuum synthesis process known as reactive ballistic deposition (RBD) is used to synthesize nanostructured bismuth vanadate (BiVO₄), which is studied for PEC water oxidation. Additionally, ballistic deposition (BD) is used to incorporate Mo and W into nanostructured BiVO₄ to improve the PEC activity. An array dispenser and scanner system is used to incorporate metals into copper oxide (CuO) and copper bismuth oxide (CuBi₂O₄) and over 3,000 unique material compositions are tested for cathodic photoactivity. The system is also used to test 35 elements as single component metal oxides, mixed metal oxides, and dopants for titanium dioxide (TiO₂) for use in dye-sensitized solar cells (DSCs). Lastly, RBD is used to deposit tungsten semicarbide (W₂C) onto p-type silicon (p-type) substrates as an electrocatalyst for PEC proton reduction. In many cases, the synthesis techniques and new material combinations presented in this dissertation result in improved PEC performance. The materials are thoroughly assessed and characterized to gain insights into their nanostructure, chemical composition, light absorption, charge transport properties, catalytic activity, and stability. / text

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Not available / text

Not available / text