In this research, CuInSe2 thin film is grown at 350¢J low temperature by photo-assisted co-evaporation system to fabricate PI (polyimide) substrate flexible thin film solar cells. The low temperature growing CuInSe2 is analyzed by raman spectroscopy. Besides, sputtering Mo thin film on PI and CIS/Mo/PI contact properties are also researched for device fabrication. By studying the Ar pressure and Mo internal stress relationship during the deposition, the Mo layer has been fabricated with both low resistivity and good adhesion. The sheet resistance of Mo layer is 1.95 £[/¡¼ and shows ohmic contact with CuInSe2 at temperature below 350¢J. Raman spectroscopy shows that photo-assisted CuInSe2 has stronger and thinner A1 peak than which without light. Two-stage growing can help eliminating Cu2Se and background signals further. CA structure vibration modes are involved in the asymmetric A1 peak broadening. The SLG/Mo/CIS/CdS/ZnO:Al/Al structured device has open voltage, Voc = 0.320 V, short cut current, Isc = 3.61 mA, and solar cell fill factor, FF = 49.8 %. On the other hand, PI/Mo/CIS/CdS/ZnO:Al/Al structured device has open voltage, Voc = 0.318 V, short cut current, Isc = 2.71 mA, and solar cell fill factor, FF = 39.0 %¡C

The motivation of this study is based on integrated passive filter dielectric thin films with thin layers. Reducing the area of integrated passive filter in a circuit by enhancing dielectric constant with same capacitance and thickness is the purpose which has been expected. To fabricate the thin film MIM structure capacitors, RF magnetron sputtering method was selected and BaNd2Ti5O14 composed materials treated as the target to grow the thin film dielectric layer in MIM structure capacitors. In this study the MIM structure capacitors were deposited on alumina substrates with Pt electrodes. In the thin film experiments, various operation parameters of sputtering deposition and post thermal process at different temperature were used to perform the desired thin film dielectric layers. In order to obtain the optimal performance of the dielectric thin films, ¡§Taguchi Method¡¨ was used as a experimental tool. The primary investigation focused on the electric characteristics of the thin film capacitors in this article. In the arranged ranges of the parameters, the optimal dielectric thin films were deposited under RF power 100W with deposition temperatures at 400¢J, chamber pressure is 10mtorr. The dielectric constant of deposited thin films is 39.2 at 1MHz, the dissipation factor is 1.38¢H at 10kHz, leakage current is 2.61X10-7A/cm2 at 5V operating voltage and breakdown electric field of 0.29MV/cm is observed. The crystalline structures of deposited thin films were characterized by XRD and found amorphous structure. Film roughness was measured by Atomic Force Microscope (AFM) with 0.263 nm.

<p>High tunability and low loss tangent of ferroelectric thinfilms offer unique opportunity for the development of variousmicrowave devices. Silver tantalate niobate, which showsexcellent microwave properties, was selected for this study.Ag(Ta,Nb)O₃(ATN) showed week dielectric dispersion in a widefrequency range from 1 kHz up to 100 GHz, negligible losses upto 30 GHz, and ease to tailor paraelectric state in a widetemperature range by Ta:Nb ratio.</p><p>This thesis is mainly based on the synthesis andcharacterization of niobate ferroelectric ATN thin films. Thinfilms for various measurements were prepared by pulsed laserdeposition and rf-magnetron sputtering techniques.</p><p>X-ray diffraction (XRD) pattern show that ATN/Pt₈₀Ir₂₀films have been found to be (001) preferentiallyoriented, while the epitaxial quality of ATN/LaAlO₃heterostructures have been ascertained. Dielectricproperties were analyzed by measuring the relationship betweendielectric permittivity and frequency as well as dielectricpermittivity and temperature. Reliable tracing of theferroelectric hysteresis polarization versus electric loopsindicate the ferroelectric state in ATN films at temperaturebelow 125 K and yields the remanant polarization of 0.4µC/cm²@ 77 K.</p><p>The fundamental current-voltage behavior in Ag(Ta,Nb)O₃ferroelectric films was measured usingMe/Ag(Ta,Nb)O₃/Pt₈₀Ir₂₀, Me = Pd, Au, Cr, and Al, vertical capacitivecell structures with different top electrodes. Various kinds ofconduction mechanisms such as Schottky emission, Poole-Frenkel,Fowler-Nordheim, and ionic conduction were classified.</p><p>Finally, by fabricating interdigital capacitors on the oxidesubstrates, the characteristics and performances of Ag(Ta,Nb)O₃varactors were examined. Au/Cr/ATN/LaAlO₃interdigital capacitors exhibited loss tangent aslow as 0.0033 @ 1 MHz, weak frequency dispersion of 5.8 % in 1kHz to 1 MHz range, tunability as high as 16.4 %,<i>K</i>-factor (tunability/tanδ) higher than 48.</p>

Thesis (Ph. D.)--School of Electrical and Computer Engineering, Georgia Institute of Technology, 2004. Directed by Nan M. Jokerst. / Vita. Includes bibliographical references (leaves 132-140).

Includes bibliographical references.

We present an experimental study of thin films of SrAl₄ on a LaAlO₃ substrate, with special emphasis on the Zintl-Klemm-type properties of the thin films that we grow using molecular beam epitaxy. We quantify the orientation and stoichiometry of the films and the surface morphology using reflection high energy electron diffraction (RHEED), x-ray diffraction (XRD) and atomic force microscopy (AFM). Furthermore, we present measurements of electronic properties using x-ray photoelectron spectroscopy (XPS) and ultraviolet spectroscopy (UPS). We determine the core level shifts due to the chemical environment in SrAl₄-films, which will underline the Zintl-Klemm character of the material. We measure the work function of (001)-oriented SrAl₄. Additionally we analyze the electronic transport properties of the grown thin films including the resistivity, carrier density and mobility. / text

The irreversible trend of replacing the conventional incandescence light bulbs and fluorescent tubes with white light emitting diodes (LEDs) aims to use less energy for lighting. Plenty of the commercially available white LEDs are made from blue LED chips with few-micron-thick gallium nitride (GaN) grown on several hundred micron thick transparent sapphire substrates, followed by coating of yellow phosphor powder on top of the chips for converting the emitted blue light to white light. Not only does such approach give the white LEDs a high colour temperature, but also introduces conversion loss from the phosphor powder. The former issue makes users feel unpleasant for living while the latter wastes energy. Therefore, a new version of phosphor-free multilayered vertically-stacked colour-tunable LED structure is proposed in this thesis such that it allows users to regulate the colour temperature of light source according to their preference. Simultaneously, the device replaces light conversion agents with direct light generation. The fabrication of the proposed device involved the use of backside laser micromachining of trenches on the substrates of the upper layers of basic colour LED chips at a size just enough to fit the wire-bonded wire of lower layer LED chips inside. With equal-sized basic colour LED chips tightly packed together, colour homogeneity of the proposed device is enhanced and thus provides the proposed device the capability to substitute the conventional RGB LED devices with basic colour LED chips separately aligned. To improve the internal quantum efficiency and light extraction of nitride-based LEDs, thin film photonic crystal LED is proposed. Light and heat trapping sapphire substrate is removed by laser lift-off (LLO), forming GaN thin film on an electrically conductive opaque substrate with better heat conductivity than sapphire. By proper etching, N-dopped GaN layer can be exposed, resulting in the formation of vertical LED. Compared with conventional lateral LEDs with sapphire substrate, carrier path of vertical LED is greatly reduced and hence achieving lower internal resistance. To further boost light extraction, the device top surface is patterned with nanopillars by nanosphere lithography. A monolayer of closely-packed silica nanospheres is patterned on the N-GaN surface by spin coating. It acts as a mask for etching the nanopillars which bandfold lights from diffracted modes to radiative modes located above the light line for extraction. A typical laser LLO process results in thin films with undopped gallium nitride (U-GaN) surface or N-GaN (after etching) faces up. If P-side up is necessary, the GaN layers are first required to attach to a temporary substrate for LLO and then the LLO exposed surface is adhered to the real substrate before temporary substrate is detached. This method is proposed to relieve the issue of light channeling inside the sapphire substrate of full colour LED micro-display panel fabricated on a single GaN on Sapphire wafer. With the elimination of sapphire, “parasitic” blue emissions from the area surrounding pixels are reduced which in turns improved the observable effects from the microspheres jet-printed on the top surface of the panel. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Graphene has been one of the most interesting and widely investigated materials in the past decade. Because of its high mobility, high current density, inherent strength, high temperature stability and other properties, scientists consider it a promising material candidate for the future all-carbon electronics. However, graphene still exhibits a number of problems such as an unknown interface structure and no sizable band gap. Therefore, the purpose of this thesis is to probe and solve these problems to make graphene suitable for electronics. The work focuses on high-quality C-face epitaxial graphene, which is grown on the (000-1) face (C-face) of hexagonal silicon carbide using the confinement-controlled sublimation method. C-face epitaxial graphene has much higher mobility compared to Si-face graphene, resulting from its special stacking order and interface structure, the latter of which is not fully understood. Thus, the first part of the work consists of a project, which is to investigate and modify the interface and the surface of C-face graphene by silicon deposition and annealing. Results of this project show that silicon can intercalate into the graphene-SiC interface and form SiC by bonding carbon atoms on the graphene surface. Another crucial problem of graphene is the absence of a band gap, which prevents graphene from becoming an ideal candidate for traditional digital logic devices. Therefore, the second project of this work is devoted to introducing a wide band gap into the graphene electronic structure by growing from a nitrogen-seeded SiC. After successful opening of a band gap, a pre-patterning method is applied to improve graphene thickness variations, orientational epitaxy, and the gapped electronic structure.

A mathematical model is developed to describe the micro/nano-scale fluid flow and heat/mass transfer phenomena in an evaporating extended meniscus, focusing on the transition film region under nonisothermal interfacial conditions. The model incorporates thermocapillary stresses at the liquid-vapor interface, a slip boundary condition on the solid wall, polarity contributions to the working fluid field, and binary mixture evaporation. The analytical results show that the adsorbed film thickness and the thin film length decrease with increasing superheat by the thermocapillary stresses, which influences detrimentally the evaporation process by degrading the wettability of the evaporating liquid film. In contrast, the slip effect and the binary mixture enhance the stability of thin film evaporation. The slip effect at the wall makes the liquid in the transition region flow with smaller flow resistance and thus the length of the transition region increases. In addition, the total evaporative heat flow rate increases due to the slip boundary condition. The mixture of pentane and decane increases the length of the thin film by counteracting the thermocapillary stress, which enhances the stability of the thin film evaporation. The polarity effect of water significantly elongates the thin film length due to the strong adhesion force of intermolecular interaction. The strong interaction force restrains the liquid from evaporation for a polar liquid compared to a non-polar liquid. In the experimental part, laser induced fluorescence (LIF) thermometry has been used to measure the microscale temperature field of a heated capillary tube with a 1 mm by 1 mm square cross section. For the temperature measurement, the calibration curve between the temperature and the fluorescent intensity ratio of Rhodamine-B and Rhodamine-110 has been successfully obtained. The fluorescent intensity ratio provides microscale spatial resolution and good temperature dependency without any possible bias error caused by illuminating light and background noise usually encountered in conventional LIF techniques. For the validation of the calibration curve obtained, thermally stratified fields established inside a glass cuvette of 10 mm width were measured. The measurement result showed a good agreement with the linear prediction. The temperature measurement in a 1 mm capillary tube could provide the feasible method of temperature measurement for the thin film region in the future.

Previous studies have attempted to probe the structure of ultra-thin Nickel silicide films as they evolve in the manufacturing process with limited success. These studies have used ultra-thin Nickel silicide films that were quenched during the manufacturer's annealing process at select temperatures. This study aims to determine the structure of quenched ultra-thin Ni-Si films using Grazing Incidence X-Ray Absorption Near Edge Spectroscopy (GI-XANES) and ab-initio calculations (FDMNES). Successful calculations were prepared for the δ and θ Ni2Si phases, as well as the Ni3Si2, NiSi and NiSi2 phases. The GI-XANES experimental data was taken at the Canadian Light Source, at the Hard X-Ray Microanalysis Beamline (HXMA). XANES and FDMNES are used to identify two phases of the ultra-thin films: the as-deposited phase as a low-ordered Ni3Si2 phase, and the epitaxial NiSi2 phase was found in samples annealed past 400˚C.