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Low-dielectric (k) films are one of the performance drivers for continued scaling of integrated circuit devices. These films are needed in microelectronic device interconnects to lower power consumption and minimize cross talk between metal lines that "interconnect" transistors. Low-k materials currently in production for the 45 and 65 nm node are most often organosilicate glasses (OSG) with dielectric constants near 2.8 and nominal porosities of 8-10%. The next generation of low-k materials will require k values 2.6 and below for the 45 nm device generation and beyond. The continuous decrease in device dimensions in ultra large scale integrated (ULSI) circuits have brought about the replacement of the silicon dioxide interconnect dielectric (ILD), which has a dielectric constant (k) of approximately 4.1, with low dielectric constant materials. Lowering the dielectric constant reduces the propagation delays, RC constant (R = the resistance of the metal lines; C = the line capacitance), and metal cross-talk between wires. In order to reduce the RC constants, a number of low-k materials have been studied for use as intermetal dielectrics. The k values of these dielectric materials can be lowered by replacing oxide films with carbon-based polymer films, incorporating hydrocarbon functional groups into oxide films (SiOCH films), or introducing porogens in the film during processing to create pores. However, additional integration issues such as damage to these materials caused by plasma etch, plasma ash, and wet etch processes are yet to be overcome. This dissertation reports the effects of plasma, temperature and chemical reactions on low-k SiOCH films. Plasma ash processes have been known to cause hydrophobic films to lose their hydrophobic methyl groups, rendering them to be hydrophilic. This allows the films to readily absorb moisture. Supercritical carbon dioxide (SC-CO2) can be used to transport silylating agents, hexamethyldisilazane (HMDS) and diethoxy-dimethlysilane (DEDMS), to functionalize the damaged surfaces of the ash-damaged films. The thermal stability of the low-k films after SC-CO2 treatment is also discussed by performing in-situ heat treatments on the films. UV curing has been shown to reduce the amount of pores while showing only a limited change dielectric constant. This work goes on to describe the effect of UV curing on low-k films after exposing the films to supercritical carbon dioxide (CO2) in combination with tetramethylorthosilicate (TMOS).

Semiconductor manufacturing defects adversely affect yield and reliability. Manufacturers expend vast resources to reduce defects within their processes. As the minimum feature size get smaller, defects become increasingly difficult to prevent. Defects can change the behavior of a logic circuit resulting in a fault. Manufacturers and designers may improve yield, reliability, and profitability by using design techniques that make products robust even in the presence of faults. Triple modular redundancy (TMR) is a fault tolerant technique commonly used to mask faults using voting outcomes from three processing elements (PE). TMR is effective at masking errors as long as no more than a single processing element is faulty. Time distributed voting (TDV) is proposed as an active fault tolerant technique. TDV addresses the shortcomings of triple modular redundancy (TMR) in the presence of multiple faulty processing elements. A faulty PE may not be incorrect 100% of the time. When a faulty element generates correct results, a majority is formed with the healthy PE. TDV observes voting outcomes over time to make a statistical decision whether a PE is healthy or faulty. In simulation, fault coverage is extended to 98.6% of multiple faulty PE cases. As an active fault tolerant technique, TDV identifies faulty PE's so that actions may be taken to replace or disable them in the system. TDV may provide a positive impact to semiconductor manufacturers by improving yield and reliability even as fault frequency increases.

The quantum confined Stark effect (QCSE) and ultrafast absorption dynamics near the bandedge have been investigated in p-i-n waveguides comprising quantum confined heterostructures grown on GaAs substrates, for emission at 1.3um. The materials are; isolated InAs/InGaAs dot-in-a-well (DWELL) quantum dots (QD), bilayer InAs quantum dots and GaInNAs multiple quantum wells (MQW). The focus was to investigate these dynamics in a planar waveguide geometry, for the purpose of large scale integration in optical systems. Initial measurements of the QCSE using photocurrent measurements showed a small shift for isolated QDs whilst a significant shift of 40nm (at 1340nm) was demonstrated for bilayer dots, comparable to that of GaInNAs MWQ (30nm at 1300nm). These are comparable to InP based quaternary multiple quantum wells used in modulator devices. With the use of a broadband continuum source the isolated quantum dots exhibit both a small QCSE (15nm at 1280nm) and minimal broadening which is desirable for saturable absorbers used in monolithic modelocked semiconductor lasers (MMSL). A robust experimental set-up was developed for characterising waveguide modulators whilst the electroabsorption and electro-refraction was calculated (dn=1.5x10⠻³) using the Kramers-Kronig dispersion relation. Pump probe measurements were performed at room temperature using 250fs pulses from an optical parametric oscillator (OPO) on the three waveguide samples. For the isolated QDs ultrafast absorption recovery was recorded from 62ps (0V) to 700fs (-10V and the shortest times shown to be due to tunneling. Additionally we have shown good agreement of the temperature dependence of these dots and the pulse width durations from a modelocked semiconductor laser using the same material. Bilayer QDs are shown to exhibit ultrafast absorption recovery from 119ps (0V) to 5ps (-10V) offering potential for applications as modelocking elements. The GaInNAs multiple quantum wells show absorption recovery of 55ps (0V), however under applied reverse bias they exhibit long lived field screening transients. These results are explained qualitatively by the spatial separation of electrons and holes at heterobarrier interfaces.

M. Tech. Digital Technology. / This dissertation reports on an optical-based two-dimensional position sensor for use in Active Magnetic Bearings (AMB) to measure the position of the levitated rotor. The motivation for the deployment of optical technology is the well-known advantage of high precision contactless displacement measurement. The radial and axial edges of the rotor are illuminated by red and green laser beams respectively. The position of the rotor is determined from its image projected on a Charge Coupled Device (CCD) sensor. The measuring principle is demonstrated as a position sampler in the closed loop control of an active magnetic bearing model. The image representing the position is processed with a real-time algorithm on a Field Programmable Logic Gate Array. The principle of operation of a CCD as a position sensor is analysed in order to establish how the image captured by the CCD can be processed to determine the position of the rotor. A simple AMB is modelled in which the sensor acts as a feedback position device. The main objective of the model is to evaluate the accuracy of the system. The purpose of the overall sensing technique to be used is to achieve highly accurate and precise measurements with CCD-based optical metrology.

Ge₂Sb₂Te₅ (GST) is an established phase-change material that undergoes fast reversible transitions between amorphous and crystalline states with a high electro-optical contrast, enabling applications in non-volatile optical and electronic memories and optically-switchable structured metamaterials. This work demonstrates that optical anisotropy can be induced and recorded in pure and doped GST thin films using circularly polarised light (CPL), opening up the possibility of controlled induction of anisotropic phase transition in these and related materials for optoelectronic and photonic applications. While the amorphous-to-crystalline phase transition in GST has generally been understood to proceed via a thermal mechanism, significant optical anisotropy (measured by circular dichroism (CD) spectroscopy in this work) strongly suggests that there is an electronic athermal component of the phase change induced by the handedness of circularly polarised nanosecond laser pulses and implies the existence of chiral structures or motifs. Optically active and inactive regions in the films have also been studied using X-ray and electron diffraction and spectroscopic techniques in order to obtain a structural picture that can be correlated to the optical changes observed and the findings offer surprising evidence of the nature of the phase transition. Regions exhibiting higher CD signal intensities were found to be mostly amorphous with elemental phase separation observed within modified surface features. Several mechanisms are proposed for the observed phenomena, including the retention of chiral crystalline fragments in laser- irradiated and melt-quenched amorphous regions, which could explain the results of CD spectroscopy. This may be extended to other material systems and harnessed in potential metamaterials, plasmonics, photonics or chiroptical applications.

The effect of hot phonons and the influence of macroscopic polarization-induced built-in fields on the performance of III-V nitride devices are investigated. Self-heating due to hot phonons is analyzed in AlGaN/GaN high electron mobility transistors (HEMTs). Thermal transport by acoustic phonons in the diffusive limit is modeled using a two-dimensional lattice heat equation. The effect of macroscopic polarization charges on the operation of blue and green InGaN-based quantum well structures is presented. To characterize these structures, the electronic part of the two-dimensional quantum well laser simulator MINILASE is extended to include nitride bandstructure and material models. A six-band k.p theory for strained wurtzite materials is used to compute the valence subbands. Spontaneous and piezoelectric polarization charges at the interfaces are included in the calculations, and their effects on the device performance are described. Additionally, k.p Hamiltonian for crystal growth directions that minimize the polarization-induced built-in fields are modeled, and valence band dispersion for the non-polar and semi-polar planes are also calculated. Finally, a design parameter subspace is explored to suggest epitaxial layer structures which maximize gain spectral density at a target wavelength for green InxGa1-xN-based single quantum well active regions. The dependence of the fundamental optical transition energy on the thickness and composition of barriers and wells is discussed, and the sensitivity of gain spectral density to design parameters, including the choice of buffer layer material, is investigated.

Indiana University-Purdue University Indianapolis (IUPUI) / In this research thesis, copper indium gallium selenium (CIGS) nanoparticles were synthesized from metal chlorides, functionalized to disperse in water, and further used in layer by layer (LbL) nanoassembly of CIGS films. CIGS nanoparticles were synthesized through the colloidal precipitation in an organic solvent. The peak and average sizes of the synthesized particles were measured to be 68 nm and 75 nm in chloroform, and 30 nm and 115 nm in water, respectively. Two methods were used to disperse the particle in water. In the first method the stabilizing agent oleylamine (OLA) was removed through multiple cleaning processes, and in the second method ligand exchange was performed with polystyrene sulfonate (PSS). Zeta potential of CIGS nanoparticles dispersed in water was measured to be +61 mV. The surface charge of the nanoparticles was reversed by raising the pH of the solution, which was measured to be −43.3 mV at 10.5 pH. In a separate process, the CIGS nanoparticles dispersed in water were coated with PSS. The resulting dispersion was observed to be stable and the surface charge was measured to be −56.9 mV. The LbL deposition process of CIGS nanoparticles was characterized by depositing thin films on quartz crystal microbalance (QCM). LbL depositions was conducted using (i) oppositely charged CIGS nanoparticles, (ii) positively charged CIGS nanoparticles and PSS, and (iii) PSS-coated CIGS (CIGS-PSS) and polyethyleneimine (PEI). The average thickness of each bi-layer of the above mentioned depositions were measured to be 2.2 nm, 1.37 nm, and 10.12 nm, respectively. The results from the QCM have been observed to be consistent with the film thickness results obtained from atomic force microscopy (AFM). Various immersion times versus thickness of the film were also studied. For electrical characterization, the CIGS films were deposited on indium tindioxide (ITO)-coated glass substrates. Current versus voltage (I/V) measurements were carried out for each of the films using the Keithley semiconductor characterization instruments and micromanipulator probing station. It was observed that the conductivity of the films was increased with the deposition of each additional layer. The I/V characteristics were also measured under the light illumination and after annealing to study the photovoltaic and annealing effects. It was observed that under light illumination, the resistivity of a 12-layer CIGS film decreased by 93% to 0.54 MΩ.m, and that of the same number of layers of PSS-coated CIGS and PEI film decreased by 60% to 0.97 MΩ.m under illumination. The resistivity of an 8-layer CIGS and PSS film decreased by 76.4% to 0.1 MΩ.m, and that of the same layers of PSS-coated CIGS and PEI decreased by 87% to 0.07 MΩ.m after annealing. The functionalized nanoparticles and the LbL CIGS films were implemented in the solar cell devices. Several configurations of CIGS films (p-type), and ZnO and CdS films (n-type) were considered. Poly(3,4-ethylenedioxythiophene) (PEDOT), molybdenum (Mo), and ITO were used as back contacts and ITO was used as front contact for all the devices. The devices were characterized the Keithley semiconductor characterization instruments and micromanipulator probing station. For a CIGS and n-ZnO films device with PEDOT as back contact and ITO as front contact, the current density at 0 V and under light illumination was measured to be 60 nA/cm2 and the power density was measured to be 0.018 nW/cm2. For a CIGS and CdS films device with ITO as both back and front contact, the current density at 0 V and under light illumination was measured to be 50 nA/cm2 and the power density was measured to be 0.01 nW/cm2. For a drop-casted CIGS and CdS films device with Mo as back contact and ITO as front contact, the current density of 50 nA/cm2 at 0 V and power density of 0.5 nW/cm2 under light illumination was measured. For the LbL CIGS and chemical bath deposited CdS films device with ITO as both back and front contact, the current density of 0.04 mA/cm2 at 0 V and power density of 1.6 μW/cm2 under light illumination was measured. Comparing to Device-III, an increase by 99% in the power density was observed by using the CIGS LbL film in the device structure. The novel aspects of this research include, (i) functionalization of the CIGS nanoparticles to disperse in water including coating with PSS, (ii) electrostatic LbL deposition of CIGS films using oppositely charged nanoparticles and polymers, and (iii) the utilization of the fabricated LbL CIGS films to develop solar cells. In addition, the n-type cadmium sulfide film (CdS) and zinc oxide (ZnO) buffer layer were also deposited through LbL process after the respective particles were functionalized with PSS coating in separate experiments.

Indiana University-Purdue University Indianapolis (IUPUI) / Fabrication and analysis of Copper Indium Gallium di-Selenide (CIGS) nanoparticles-based thin film solar cells are presented and discussed. This work explores non-traditional fabrication processes, such as spray-coating for the low-cost and highly-scalable production of CIGS-based solar cells. CIGS nanoparticles were synthesized and analyzed, thin CIGS films were spray-deposited using nanoparticle inks, and resulting films were used in low-cost fabrication of a set of CIGS solar cell devices. This synthesis method utilizes a chemical colloidal process resulting in the formation of nanoparticles with tunable band gap and size. Based on theoretical and experimental studies, 100 nm nanoparticles with an associated band gap of 1.33 eV were selected to achieve the desired film characteristics and device performances. Scanning electron microcopy (SEM) and size measurement instruments (Zetasizer) were used to study the size and shape of the nanoparticles. Electron dispersive spectroscopy (EDS) results confirmed the presence of the four elements, Copper (Cu), Indium (In), Gallium (Ga), and Selenium (Se) in the synthesized nanoparticles, while X-ray diffraction (XRD) results confirmed the tetragonal chalcopyrite crystal structure. The ultraviolet-visible-near infra-red (UV-Vis-NIR) spectrophotometry results of the nanoparticles depicted light absorbance characteristics with good overlap against the solar irradiance spectrum. The depositions of the nanoparticles were performed using spray-coating techniques. Nanoparticle ink dispersed in ethanol was sprayed using a simple airbrush tool. The thicknesses of the deposited films were controlled through variations in the deposition steps, substrate to spray-nozzle distance, size of the nozzle, and air pressure. Surface features and topology of the spray-deposited films were analyzed using atomic force microscopy (AFM). The deposited films were observed to be relatively uniform with a minimum thickness of 400 nm. Post-annealing of the films at various temperatures was studied for the photoelectric performance of the deposited films. Current density and voltage (J/V) characteristics were measured under light illumination after annealing at different temperatures. It was observed that the highest photoelectric effect resulted in annealing temperatures of 150-250 degree centigrade under air atmosphere. The developed CIGS films were implemented in solar cell devices that included Cadmium Sulfide (CdS) and Zinc Oxide (ZnO) layers. The CdS film served as the n-type layer to form a pn junction with the p-type CIGS layer. In a typical device, a 300 nm CdS layer was deposited through chemical bath deposition on a 1 $mu$m thick CIGS film. A thin layer of intrinsic ZnO was spray coated on the CdS film to prevent shorting with the top conductor layer, 1.5 μm spray-deposited aluminum doped ZnO layer. A set of fabricated devices were tested using a Keithley semiconductor characterization instrument and micromanipulator probe station. The highest measured device efficiency was 1.49%. The considered solar cell devices were simulated in ADEPT 2.0 solar cell simulator based on the given fabrication and experimental parameters. The simulation module developed was successfully calibrated with the experimental results. This module can be used for future development of the given work.

M. Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / In chemical bath deposition (CBD) method, deposition of metal chalcogenide semiconducting thin films occurs due to substrate maintained in contact with a dilute chemical bath containing metal and chalcogenide ions. Semiconducting nickel sulphide (NiS) and iron sulphide (FeS) thin films have been prepared on a glass substrate by varying the deposition parameters such as the concentration of solutions, deposition time, temperature and pH. Multi-layered thin films were deposited on glass substrate and the spin-cast conductive polymer, poly (3.4-ethylenedioxythiopene) polystyrene sulfonate (PEDOT: PSS) was intercalated. The characterization of the films was carried out using UV-Vis spectroscopy, scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and X-ray diffraction (XRD). Single layer nickel sulphide was deposited at room temperature, pH 10 and the deposition period of 3 hours, triethanolamine was used as the complexing agent. Iron sulphide was deposited for 6 hours at 70 °C with the pH of 2.5 using EDTA as a complexing agent. Generally the iron and nickel sulphide were prepared from their respective nickel or iron salt and the thiourea or thiosulfate as a source of sulphide ions in solution. SEM and AFM results show that the FeS film is evenly coated and has uniform grain size with the roughness of ~22.4 nm and thickness of ~23.8 nm. The optical absorption analysis of FeS showed the band gap energy of ~2.9 eV which blue shifted from the bulk. The EDX analysis confirms the compositions of iron and sulphur in FeS films. XRD pattern showed amorphous films for both FeS and NiS thin films due to the amorphous nature of the glass substrate. The optical data of NiS film were analysed and exhibited the band gap energy of ~3.5 eV and ~3.3 eV for successive ionic layer adsorption and reaction (SILAR), which is the modified CBD, both blue shifted from the bulk. The films were observed to have thickness value of ~35.7 nm and ~2.3 nm SILAR with the roughness of ~112.5 nm and ~35.4 nm SILAR from AFM results. SEM confirmed the uniformly distributed film presented by AFM analysis. The chemical composition of Ni and S were confirmed by EDX spectra. The PEDOT: PSS was intercalated between the FeS as the first layer and NiS as the top layer which gave the thickness of ~18.7 nm and roughness of ~115.2 nm from AFM analysis. PEDOT: PSS acted as a passive layer that protects and stabilize the FeS layer and NiS as the third active layer which enhanced the optical absorption of the film when using SILAR method for solar application.