This dissertation presents a comprehensive study of the intrinsic room temperature ferromagnetism, RTFM, in technologically important thin films of ZnO, MgO, Mg@ZnO, the so-called d0–magnets that do not contain any intrinsic magnetic elements. We also present the first report on magnetism in Mn doped MgO films fabricated by dc magnetron sputtering. We have just published (April 2013 ‘on-line’) a state of the art review entitled ‘p-type ZnO Theory, growth, properties, and devices’ in the prestigious journal ‘Progress in Materials Science’, summarizing the recent advances of the studies on p-type ZnO thin films and pointing out the major challenges that remain in the field. The experimental work then focuses on the magnetic properties of band gap engineered Mg@ZnO films exploiting the fact that by substitutional doping of Mg for Zn in ZnO it is possible to tailor new materials with bandgap energy in the range 3.3 eV to 7.2 eV, thus extending the possibilities for new magnetic and optical device applications. In addition, we show that by doping Mn in MgO its magnetic properties can be enhanced to saturation values as high as 38.5 emu/cm3 in a 92 nm thick film. These studies involve extensive characterization of the high quality films in the thickness range of nanometers, using SQUID magnetometer for magnetic properties, XRD for structural analysis, Dual beam HRSEM/FIB and AFM for accurate film cross-sectioning and surface morphology, EDXS for elemental analysis, UV-VIS NIR for measuring the band gap of MgxZn(1-x)O films, Mg K-edge NEXAFS experiment in order to understand electronic structure of specific cations present in the thin films The origin of the observed room temperature feerromaganetism is attributed to cation vacancies and its consequences on the polarization about these vacancies in the oxides... ZnO films are promising materials for optoelectronic device applications, and the fabrications of high quality p-type ZnO and p–n junction are the key steps to realize these applications. However, reliable p-type doping of the material remains a major challenge because of the self-compensation from native donor defects (VO and Zni) and/or hydrogen incorporation. Considerable efforts to obtain p-type ZnO by doping different elements with various techniques have resulted in remarkable progress in the field both from theoretical and experimental point of view. In our paper, we discuss p-type ZnO materials: theory, growth, properties and devices, comprehensively. We first discuss the native defects in ZnO. Among the native defects in ZnO, VZn and Oi act as acceptors. We then present the theory of p-type doping in ZnO, and summarize the growth techniques for p-type ZnO and the properties of p-type ZnO materials. Experimentally, besides the intrinsic p-type ZnO grown at O-rich ambient, p-type ZnO (MgZnO) materials have been prepared by various techniques using Group-I, IV and V elements. We pay a special attention to the band gap of p-type ZnO by band gap engineering and room temperature ferro magnetism observed in p-type ZnO. Finally, we summarize the devices based on p-type ZnO materials. In presenting the current studies, we first focus on the sputtering process in order to produce high quality films. From a comparative study of RTFM, in MgO films deposited by sputtering from 99.999% pure metallic Mg, Vs MgO targets respectively on glass/Si substrates under identical ambience during deposition it is found that the metallic targets give the best magnetic properties (e.g: with maximum Ms values of ~13.75 emu/g vs ~ 4.2 emu/g respectively on Si substrates.(supplement 2). Furthermore, the Ms values are strongly film thickness dependent with Mg target while it is weakly so for films from MgO target. Also, the as deposited MgO films using metallic Mg target are found to be amorphous, while it is nanocrystalline when the films are sputtered off MgO targets. The overall Ms values are found to be dependent on the oxygen content in the atmosphere during deposition, increasing to 2.69 emu/g at a oxygen partial pressure of 40% of the total working gas pressure. On annealing to nanocrystallize these films in the temperature range 600 to 8000C strong XRD peaks corresponding to (200) orientation are observed, and Ms values decrease proportionately. (supplement 3). With the above information on studies for optimizing the effect of sputtering gas, film thickness, and oxygen partial pressure, PO2, comprehensive investigations on band gap engineering and magnetism in MgxZn(1-x)O co-sputtered thin films from Mg and Zn targets are then closely examined. The optical band gap calculated from absorption spectra shows that the band gaps of Mg-doped ZnO thin films increased linearly from 3.33 to 4.074 eV. Our studies indicate that both the magnetic properties and the band gap of the film can be tailored by tuning the film thickness and PO2 in the working gas. In summary, RTFM ordering in the thin films originates from cation vacancies which couple ferromagnetically and establish long range magnetic order. The ferromagnetic ordering in these materials is shown to arise from defects situated at the cation sites. Electronic structure studies of some selected films disclose that the unoccupied O 2p states exist and this unoccupied state results from cation vacancy (VMg). / <p>QC 20130524</p>

An innovative approach for characterization of one dimensional Photonic Band Gap structures comprised of metallic inclusions (i.e. subwavelength dipole elements or resonant ring elements) is presented. Through an efficient S- to T-parameters conversion technique, a detailed analysis has been performed to investigate the variation of the dispersion characteristics of 1-D PBG structures as a function of the cell element configuration. Also, for the first time, the angular sensitivity of the structure has been studied in order to obtain the projected band diagrams for both TE and TM polarizations. Polarization sensitivity of the subwavelength cell element is exploited to propose a novel combination of elements which allows achieving PBGs with simultaneous frequency and polarization selectivity. The proposed approach demonstrates that the dispersion characteristic of each orthogonal polarization can be independently adjusted with dipole elements parallel to that same polarization. Generally, the structure has potential applications in orthomode transducer, and generally whenever the polarization of the incoming signal is to be used as a means of separating it from another signal in the same frequency band that is of orthogonal polarization. The current distribution and the resonance behavior of the ring element is studied and the effect of resonance on dispersion characteristics of 1-D PBGs composed of rings is investigated for the first time, for both individual and coupled rings. Interestingly, it is observed that 1-D PBG composed of resonant elements consistently has a bandgap around the resonant frequency of the single layer structure.

Cette étude a pour objet d'apporter des éléments de compréhension quant à l'amélioration de la résistance à la corrosion des alliages de ZnMg(Al), en comparaison du Zn, en milieu atmosphérique chloré. Le cheminement de réflexion part de considérations fondamentales et tend vers des conditions réelles d'utilisation. La première étape a consisté à synthétiser et caractériser des films de ZnO dopé Mg et notamment l'évolution de la structure cristalline, la structure électronique, la résistivité, (...) avec le dopage. La pertinence de ces paramètres a ensuite été évaluée et discutée au regard de la stabilité de ces films en solution. Dans un second temps, les produits de corrosion formés, en laboratoire, en présence ou non de chlorures, sur des phases pures de Zn et ZnMg, ont été caractérisés. Les processus physico-chimiques liés à la formation de ces produits ont ensuite été discutés, afin de mettre en lumière le rôle du Mg dans l'amélioration de la résistance à la corrosion. La dernière étape, s'est attachée à caractériser des produits de corrosion formés après 6 mois en milieu naturel, en atmosphère marine, sur des phases pures de Zn et ZnMg, et des revêtements industriel de type ZnMgAl. Les résultats obtenus ont permis de mettre en évidence une meilleure stabilité en solution des films de Zn0.84Mg0.16O en comparaison du ZnO, en corrélation avec une présence accrue de liaisons hydroxyles, une augmentation de la résistivité et de la fonction de travail. Ces trois paramètres sont apparus également pertinents, sur les produits de corrosion formés en laboratoire et naturellement en présence de Mg et de Mg, Al, et corrélés à l'amélioration de la résistance à la corrosion.

A systematic study of trends in band gap and lattice energies for bare zinc oxide nanoparticles were performed by means of quantum chemical density functional theory (DFT) calculations and density of states (DOS) calculations. The geometry of the optimized structures and the appearance of their frontier orbitals were also studied. The particles studied varied in sizes from (ZnO)6 up to (ZnO)192.The functionalization of bare and hydroxylated ZnO surfaces with MPTMS was studied with emphasis on the adsorption energies for adsorption to different surfaces and the effects on the band gap for such adsorptions.

Transport Properties of Wide Band Gap Semiconductors Louis Tirino III 155 pages Directed by Dr. Kevin F. Brennan The objective of this research has been the study of the transport properties and breakdown characteristics of wide band gap semiconductor materials and their implications on device performance. Though the wide band gap semiconductors have great potential for a host of device applications, many gaps remain in the collective understanding about their properties, frustrating the evaluation of devices made from these materials. The model chosen for this study is based on semiclassical transport theory as described by the Boltzmann Transport Equation. The calculations are performed using an ensemble Monte Carlo simulation method. The simulator includes realistic, numerical energy band structures derived from an empirical pseudo-potential method. The carrier-phonon scattering rates and impact ionization transition rates are numerically evaluated from the electronic band structure. Several materials systems are discussed and compared. The temperature-dependent, high-field transport properties of electrons in gallium arsenide, zincblende gallium nitride, and cubic-phase silicon carbide are compared. Since hole transport is important in certain devices, the simulator is designed to simulate electrons and holes simultaneously. The bipolar simulator is demonstrated in the study of the multiplication region of gallium nitride avalanche photodiodes.

Photonic crystals, periodic dielectric structures that control photons in a similar way that atomic crystals control electrons, present opportunities for the unprecedented control of light. Photonic crystals display a wide gamut of properties, such as the photonic band gap, negative index of refraction, slow or stationary modes, and anomalous refraction and propagation effects. This thesis investigates the modeling, simulation, fabrication, and measurement of two-dimensional square lattice photonic crystals. An effective index model was developed to describe the propagation of electromagnetic waves in the media and applied to characterize the behavior of self-collimated beams to discern the effect of the photonic crystal on the evolution of the amplitude and phase of the propagating beam. Potential applications include optical interconnects and stand alone devices such as filters and lasers. Based on design parameters from the simulations, two dimensional photonic crystals were fabricated on amorphous and single crystal silicon-on-insulator substrates utilizing electron beam lithography and inductively coupled plasma etching. A unique etching process utilizing a combination of Cl2 and C4F6 gases was developed and characterized which displayed a vertical profile with a sidewall angle of under 1 degree from vertical and very smooth sidewalls for features as small as 150 nm. The high quality of the etching was the key to obtaining extremely low loss, low noise structures, making feasible the fabrication of large area photonic crystal devices that are necessary to measure propagation phenomena. Reflectivity measurements were used to directly observe the photonic band structure with excellent correlation with theory. A device was designed and fabricated which successfully verified the prediction of the simulations through measurements of the self-collimation effect across a broad range of infrared wavelengths. A solid foundation for the necessary components (simulation, modeling, design, fabrication, and measurement) of two-dimensional photonic crystal has been demonstrated. Elements from solid state physics, materials science, optics, and electromagnetics were incorporated to further the understanding of the mechanism of beam propagation in photonic crystals and illuminating the vast potential of research in periodic media.

The absence of appropriate media to cultivate photons efficiently at the micro or nano scale has hindered taking the full advantage of processing information with light. The proposal of such a medium for light, known as photonic crystals (PCs)--multi-dimensional artificially periodic dielectric media--brings the possibility of a revolution in communications and sensing much closer. In such media, one can manipulate light at a scale on the order of the wavelength or even shorter. Applications of PCs other than in communication include bio-sensing because of the peculiar properties of PCs such as the capability of enhance field-matter interaction and control over the group velocity. As a result, PC waveguide (PCW) structures are of interest and it is expected that PC sensors offer the feasibility of multi-analyte and compact sensing schemes as well as the ability of the detection of small absolute analyte quantities (nanoliters) and low-concentration samples (picomoles), which may be advantages over conventional approaches such as fiber optic and slab waveguide sensors. Depending on the nature of the analyte, either dispersive or absorptive sensing schemes may be implemented. Light propagation is controlled fully only with 3D PCs. One of the problems arising due to reducing the dimension to 2D is that PCs become strongly polarization sensitive. In many cases, one wants to implement polarization insensitive devices such that the PC provides a full band gap for all polarizations. To address this problem, a novel type of PC called annular PC is proposed and analyzed. The capability of tuning the TE and TM polarizations independently within the same structure provides great flexibility to produce polarization-independent or polarization-dependent devices as desired. PCW bends are expected to be the essential building blocks of photonic integrated circuits. Sharp corners having small radii of curvature can be obtained. To enhance the low-loss and narrow-band transmission through these bends, PC heterostructures waveguide concept is introduced. We show that in PCWs formed by joining different types of PCs in a single structure, light can flow around extremely sharp bends in ways that are not possible using conventional PCWs based on a single type of PC.

Optical properties of Tl4In3GaSe8, Tl4InGa3Se8, Tl4In3GaS8, Tl2InGaS4 and Tl4InGa3S8 chain and layered crystals were studied by means of photoluminescence (PL) and transmission-reflection experiments. Several emission bands were observed in the PL spectra within the 475-800 nm wavelength region. The results of the temperature- and excitation intensity-dependent PL measurements in 15-300 K and 0.13&times / 10-3-110.34 W cm-2 ranges, respectively, suggested that the observed bands were originated from the recombination of electrons with the holes by realization of donor-acceptor or free-to-bound type transitions. Transmission-reflection measurements in the wavelength range of 400-1100 nm revealed the values of indirect and direct band gap energies of the crystals studied. By the temperature-dependent transmission measurements in 10-300 K range, the rates of change of the indirect band gap of the samples with temperature were found to be negative. The oscillator and dispersion energies, and zero-frequency refractive indices were determined by the analysis of the refractive index dispersion data using the Wemple&ndash / DiDomenico single-effective-oscillator model. Furthermore, the structural parameters of all crystals were defined by the analysis of X-ray powder diffraction data. The determination of the compositional parameters of the studied crystals was done by energy dispersive spectral analysis experiments.

A new class of &pi / -conjugated monomers was synthesized with combination of electron donating and electron-withdrawing heterocyclics to understand the effects of structural differences on electrochemical and optoelectronic properties of the resulting polymers. Electron deficient benzotriazole, substititued with benzyl from two available sites, coupled with stannylated electron donating groups, ethylenedioxythiophene (EDOT) and thiophene (Th), to yield four different monomers / 1-benzyl-4,7-di(thiophen-2-yl))-2H-benzo[d][1,2,3] triazole (BBTA), 2-benzyl-4,7-di(thiophen-2-yl))-2H-benzo[d][1,2,3] triazole (BBTS), 1-benzyl-4,7-bis(2,3-dihydrothieno[3,4-b]dioxin-5-yl)-2H-benzo [d][1,2,3]triazole (BBTEA), 2-benzyl-4,7-bis(2,3-dihydrothieno[3,4-b]dioxin-5-yl)-2H-benzo [d][1,2,3]triazole (BBTES). Furthermore, EDOT and thiophene terminated napthalene-2,3-crown ether containing monomers, 14,19-di(thiophen-2-yl)-naphtho[2,3-b][1,4,7,10,13] pentaoxacyclo pentadecane (TNCT), 14,19-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-naphtho[2,3-b][1,4,7,10,13]pentaoxacyclopenta decane (ENCE), were synthesized to observe the effect crown ether moiety on the final electrochemical and optoelectronic properties of resultant polymers. Cyclic voltammetry, UV-Vis-NIR spectroscopy and colorimetry techniques were employed to examine electrochemical and optoelectronic properties of all monomers and polymers. Experimental results showed that alteration of substituent, substitution position and donor groups&rsquo / strength lead to obtain polymers with different redox behaviors, optical band gaps and different number of achievable colored states.

The demands of consumer electronic products to support multi-functionality such as computing, communication and multimedia applications with reduced form factor and low cost is the driving force behind packaging technologies such as System on Package (SOP). SOP aims to enhance the functionality of the package while providing form factor reduction by the integration of active and passive components. However, embedding components within mixed signal packages causes unwanted interferences across the digital and analog-radio frequency (RF) sections of the package, which is a major challenge yet to be addressed. This dissertation focused on the chip-last method of embedding chips within cavities in organic packages and addressed the challenges for preserving power integrity in such packages. The challenges associated with electromagnetic coupling in packages when chips are embedded within the substrate layers are identified, analyzed and demonstrated. The presence of the chip embedded within the package introduces new interaction mechanisms between the chip and package that have not been encountered in conventional packages with surface mounted chips. It is of significant importance to understand the chip-package interaction mechanisms, for ensuring satisfactory design of systems with embedded actives. The influence of the electromagnetic coupling from the package on the bulk substrate and bond-pads of the embedded chip are demonstrated. Solutions that remedy the noise coupling using Electromagnetic Band-Gap structures (EBGs) along with design methodologies for their efficient implementation in multilayer packages are proposed. This dissertation presents guidelines for designing efficient power distribution networks in multilayer packages with embedded chips.