Doctor of Philosophy / Department of Chemical Engineering / James H. Edgar / Hexagonal boron nitride (hBN) is a wide bandgap III-V semiconductor that has seen new interest due to the development of other III-V LED devices and the advent of graphene and other 2-D materials. For device applications, high quality, low defect density materials are needed. Several applications for hBN crystals are being investigated, including as a neutron detector and interference-less infrared-absorbing material. Isotopically enriched crystals were utilized for enhanced propagation of phonon modes. These applications exploit the unique physical, electronic and nanophotonics applications for bulk hBN crystals. In this study, bulk hBN crystals were grown by the flux method using a molten Ni-Cr solvent at high temperatures (1500°C) and atmospheric pressures. The effects of growth parameters, source materials, and gas environment on the crystals size, morphology and purity were established and controlled, and the reliability of the process was greatly improved. Single-crystal domains exceeding 1mm in width and 200μm in thickness were produced and transferred to handle substrates for analysis. Grain size dependence with respect to dwell temperature, cooling rate and cooling temperature were analyzed and modeled using response surface morphology. Most significantly, crystal grain width was predicted to increase linearly with dwell temperature, with single-crystal domains exceeding 2mm in at 1700°C. Isotopically enriched ¹⁰B and ¹¹B hBN crystal were produced using a Ni-Cr-B flux method, and their properties investigated. ¹⁰B concentration was evaluated using SIMS and correlated to the shift in the Raman peak of the E[subscript 2g] mode. Crystals with enrichment of 99% ¹⁰B and >99% ¹¹B were achieved, with corresponding Raman shift peaks at 1392.0 cm⁻¹ and 1356.6 cm⁻¹, respectively. Peak FWHM also decreased as isotopic enrichment approached 100%, with widths as low as 3.5 cm⁻¹ achieved, compared to 8.0 cm⁻¹ for natural abundance samples. Defect selective etching was performed using a molten NaOH-KOH etchant at 425°C-525°C, to quantify the quality of the crystals. Three etch pit shapes were identified and etch pit width was investigated as a function of temperature. Etch pit density and etch pit activation energy was estimated at 5×10⁷ cm⁻² and 60 kJ/mol, respectively. Screw and mixed-type dislocations were identified using diffraction-contrast TEM imaging.

Cette thèse porte sur le développement des méthodes d'analyse structurale de la couche mince de GaP epitaxiées sur le substrat de silicium par l'épitaxie par jets moléculaires (MBE), basées sur la diffraction des rayons X (ORX) et combinées à des techniques complémentaires telles que la microscopie électronique en transmission (TEM), la microscopie à force atomique (AFM) et la microscopie à effet tunnel (STM). Le travail est centré sur la caractérisation quantitative de la densité des défauts cristallins comme les micro-macles et les domaines d'inversion présents dans la couche ainsi que l'évaluation de la qualité de surface et l'interface. L'objectif ultime est d'obtenir une plate-forme GaP/Si parfaitement cristallisée sans défaut, via l'optimisation des paramètres de croissance. Nous avons mis en place et utilisé deux méthodes de quantification des micro-macles par la diffraction des rayons X en condition de laboratoire : les figures de pôles pour la visualisation rapide et l'évaluation de la densité des micro-macles et les « rocking-curves » permettent une extraction précise de la faction volumique de domaine maclé. Les propriétés structurales de la plate-forme de GaP/Si ont été considérablement améliorées, après une procédure d'optimisation impliquant la température de croissance, une procédure de croissance alternée (MEE) et une séquence de croissance en deux étapes. Un échantillon quasiment sans micro-macles a été obtenu par le dépôt de 40 monocouches de GaP par MEE à 350 •c suivi d'une surcroissance de 40 nm de GaP par MBE continue, à 500 •c. La surface de l'échantillon est lisse avec une rugosité de 0.3 nm. L'évaluation des domaines d'inversion par la ORX a été effectuée sur les cartographies de l'espace réciproque centrées sur les réflexions GaP de type (OOL), en laboratoire et sur une ligne synchrotron. Les balayages « transverses » extrait à partir des cartographies de l'espace réciproque sont analysés via une méthode dite "Williamson-Hall like", afin d'obtenir la "mosaïcité" qui est reliée à la micro-désorientation des petits domaines cristallins et la longueur de corrélation latérale correspondant à ces petits domaines. La distance moyenne entre parois de domaines d'inversion et ensuite estimé à partir de cette mesure. En utilisant cette méthode d'analyse et les techniques microscopiques, une optimisation plus poussée a été effectuée sur la dose de Ga au stade initial de croissance, l'utilisation de couches de marqueur AIGaP et l'homoépitaxie d'une couche de silicium avant le GaP. Enfin, nous avons obtenu un échantillon ne présentant pas de signal de micro-macle détectable en conditions standard de laboratoire, et une très faible densité de domaine d'inversion. Nous avons aussi observé une interface de GaP/Si visiblement présentant des bi-marches atomiques très régulières, sur un échantillon avec une couche de silicium déposée avant la croissance du GaP. / This thesis deals with the development of structural analysis methods of the GaP thin layers heterogeneously grown on the Si substrate by Molecular Beam Epixay (MBE), based on X-ray diffraction (XRD) analyses, combined with complementary techniques such as transmission electron microscopy (TEM), atomic force microscopy techniques (AFM) and scanning tunneling microscope (STM). The main work is centered on the quantitative characterization of crystalline defect such as micro-twins and the anti-phase domains, and the evaluation of the surface and interface quality. The ultimate goal is to achieve a perfectly crystallized GaP/Si platform without any defect, through the optimization of the growth conditions. We have applied two micro-twin quantification methods using a XRD lab setup. Pole figure method for fast visualization and evaluation of micro-twin density and rocking curves integration for a more precise absolute quantification of the micro-twin volume fraction. The GaP/Si platform structural properties have been significantly improved, after an optimization procedure involving growth temperature, MEE (Migration Enhanced Epitaxy) growth procedure and a twostep growth sequence. GaP layers quasi-free of MTs are obtained, with a r.m.s. roughness of only 0.3 nm. The APD evaluation by XRD has been performed on reciprocal space maps (RSM) centered on the (OOL) GaP reciprocal space lattice point either in lab setup or on synchrotron. Analysis of the transverse scans extracted from such RSM through the "Willamson-Hall like" method permits obtaining the "mosaicity" that is related to the micro-orientation of the small crystalline domains in the GaP layer, and the lateral correlation length which is considered to be related to the mean distance between two APBs, provided that this distance is approximately homogenous and corresponding to the mean APD size, and the density of other defects are very weak so that their influence can be neglected. Using this analytical method and the microscopic techniques, further optimization has been carried out on Ga amount at the initial growth stage, the use of AIGaP marker layers and the homoepitaxie of Si buffer layer. Finally, sample with none MT signal and very low density of APD has been achieved. Moreover, an abrupt GaP/Si interface displaying regular and double atomic steppes is observed on sample with a Si buffer layer prior to the GaP growth.

This study focuses on the development of InAs/GaInSb strained-layer superlattice structures by metal organic chemical vapour deposition (MOCVD), and deals with two aspects of the development of InAs/GaInSb SLS’s by MOCVD viz. the deposition of nano-scale (~100 Å) GaInSb layers, and the electrical characterization of unstrained InAs. The first part of this work aims to study the MOCVD growth of GaInSb layers in terms of deposition rate and indium incorporation on the nano-scale. This task is approached by first optimizing the growth of relatively thick (~2 μm) epitaxial films, and then assuming similar growth parameters during nano-scale deposition. The GaInSb layers were grown as part of GaInSb/GaSb quantum well (QW) structures. By using this approach, the GaInSb QW’s (~100 Å) could be characterized with the use of photoluminescence spectroscopy, which, when used in conjunction with transmission electron microscopy and/or X-ray diffractomery, proves useful in the analysis of such small scale deposition. It is shown that the growth rate of GaInSb on the nano-scale approaches the nominal growth rates determined from thick (~2 μm) GaInSb calibration layers. The In incorporation efficiency in nano-layers, however, was markedly lower than what was predicted by the GaInSb calibration layers. This reduction in indium incorporation could be the result of the effects of strain on In incorporation. The choice of substrate orientation for QW deposition was also studied. QW structures were grown simultaneously on both (100) and 2°off (100) GaSb(Te) substrates, and it is shown that growth on non-vicinal substrates is more conducive to the deposition of high quality QW structures. The second part of this study focuses on the electrical characterization of unstrained InAs. It is long known that conventional Hall measurements cannot be used to accurately characterize InAs epitaxial layers, as a result of parallel conduction resulting from surface and/or interface effects. This study looks at extracting the surface and bulk electrical properties of n-type InAs thin films directly from variable magnetic field Hall measurements. For p-type InAs, the situation is complicated by the relatively large electron to hole mobility ratio of InAs which tends to conceal the p-type nature of InAs thin films from Hall measurements. Here, this effect is illustrated by way of theoretical simulation of Hall data.

The importance of infrared (IR) technology (for detection in the 3-5 μm and 8-14 μm atmospheric windows) has spread from military applications to civilian applications since World War II. The commercial IR detector market in these wavelength ranges is dominated by mercury cadmium telluride (MCT) alloys. The use of these alloys has, however, been faced with technological difficulties. One of the materials that have been tipped to be suitable to replace MCT is InAs/InxGa1-xSb strained layer superlattices (SLS’s). Atmospheric pressure metal-organic vapour phase epitaxy (MOVPE) has been used to grow InAs/GaSb strained layer superlattices (SLS’s) at 510 °C in this study. This is a starting point towards the development of MOVPE InAs/InxGa1-xSb SLS’s using the same system. Before the SLS’s could be attempted, the growth parameters for GaSb were optimised. Growth parameters for InAs were taken from reports on previous studies conducted using the same reactor. Initially, trimethylgallium, a source that has been used extensively in the same growth system for the growth of GaSb and InxGa1-xSb was intended to be used for gallium species. The high growth rates yielded by this source were too large for the growth of SLS structures, however. Thus, triethylgallium (rarely used for atmospheric pressure MOVPE) was utilized. GaSb layers (between 1 and 2 μm thick) were grown at two different temperatures (550 °C and 510 °C) with a varying V/III ratio. A V/III ratio of 1.5 was found to be optimal at 550 °C. However, the low incorporation efficiency of indium into GaSb at this temperature was inadequate to obtain InxGa1-xSb with an indium mole fraction (x) of around 0.3, which had previously been reported to be optimal for the performance of InAs/InxGa1-xSb SLS’s, due to the maximum splitting of the valence mini bands for this composition. The growth temperature was thus lowered to 510 °C. This resulted in an increase in the optimum V/III ratio to 1.75 for GaSb and yielded much higher incorporation efficiencies of indium in InxGa1-xSb. However, this lower growth temperature also produced poorer surface morphologies for both the binary and ternary layers, due to the reduced surface diffusion of the adsorbed species. An interface control study during the growth of InAs/GaSb SLS’s was subsequently conducted, by investigating the influence of different gas switching sequences on the interface type and quality. It was noted that the growth of SLS’s without any growth interruptions at the interfaces leads to tensile strained SLS’s (GaAs-like interfaces) with a rather large lattice mismatch. A 5 second flow of TMSb over the InAs surface and a flow of H2 over GaSb surface yielded compressively strained SLS’s. Flowing TMIn for 1 second and following by a flow of TMSb for 4 seconds over the GaSb surface, while flowing H2 for 5 seconds over the InAs surface, resulted in SLS’s with GaAs-like interfacial layers and a reduced lattice mismatch. Temperature gradients across the surface of the susceptor led to SLS’s with different structural quality. High resolution x-ray diffraction (HRXRD) was used to determine the thicknesses as well as the type of interfacial layers. The physical parameters of the SLS’s obtained from simulating the HRXRD spectra were comparable to the parameters obtained from cross sectional transmission electron microscopy (XTEM) images. The thicknesses of the layers and the interface type played a major role in determining the cut-off wavelength of the SLS’s.

Les nanofils semiconducteurs suscitent un vif intérêt tant pour leurs propriétés fondamentales originales que pour leurs applications potentielles en opto- et nano-Électronique. La physique des nanofils et en particulier des matériaux à la base est difficile à caractériser. Dans ce contexte, la simulation numérique peut apporter des réponses quantitatives aux problèmes posés par ces objets et aider à explorer leur potentiel. En particulier, leur cristallisation se fait dans une phase hexagonale wurtzite mais avec des fautes d’empilement qui donnent lieu à des insertions de séquence cubique. La structure cubique blende de zinc a été largement étudiée, les différents aspects physiques des semiconducteurs l’adoptant sont bien illustrés dans la littérature. Par contre, ils sont mal compris en phase wurtzite. C’est pourquoi, l’étude des propriétés structurales et électroniques des cristaux III-V et hétérostructures wurtzite a fait l’objet du présent travail. En particulier, je me suis intéressée à déterminer les paramètres structuraux et électroniques d’ InAs et InP. Pour aborder ces problématiques il convient de trouver une méthode théorique adaptée. Dans ce contexte, les modélisations ab initio permettent d’explorer les propriétés globales sans une connaissance expérimentale à priori des systèmes étudiés. Elles reposent sur la résolution variationnelle de l’équation de Schrödinger qui est lourde d’un point de vue computationnel. Il existe donc toute une hiérarchie de modèles plus ou moins sophistiqués qui approchent plus ou moins la solution exacte du problème. Dans le cadre de ce travail, j’ai utilisé la théorie de la fonctionnelle de la densité qui reproduit les résultats expérimentaux de structures mais peine à évaluer les niveaux énergétiques vides. Cette difficulté est due à la définition des effets à N corps et notamment aux effets de corrélation entre les électrons. L’erreur dans l’évaluation des énergies est corrigée grâce à la correction apportée par l’approximation GW ou les fonctionnelles hybrides. Ainsi, j’ai pu obtenir des structures électroniques correctes et exploitables afin de déterminer les potentiels de déformation. Il est notamment possible de faire varier la composition des nanofils de long de leur axe de croissance afin d’y introduire des jonctions p-N, des boîtes quantiques ou des barrières tunnel. Ces hétérostructures offrent de multiples opportunités : la faisabilité de transistors, de diodes à effet tunnel résonant ou de dispositifs à un électron basés sur les nanofils de silicium ou de III-V a ainsi déjà été démontrée. Ces matériaux permettent de réaliser des hétérostructures inédites car ils peuvent s’accommoder de forts désaccords de maille en déformant leur surface. La relaxation des contraintes structurales a toutefois un impact important sur leurs propriétés électroniques et optiques. Un des paramètres importants pour bien comprendre le comportement de ces structures quantiques est l’offset électronique ou la discontinuité énergétique. Il a été calculé pour le système InAs/InP et confronté à des études expérimentales suivant les directions de croissance. / Semiconductor nanowires are attracting much attention both for their original properties and their potential applications in opto- and nanoelectronics. The physics of nanowires and in particular materials at the base is poorly understood and difficult to characterize. In this context, the numerical simulation can provide quantitative answers to the problems posed by these objects and help to explore their potential. In particular, their crystallization is in a wurtzite (WZ) hexagonal phase but with stacking faults that result in insertions of cubic sequences. The zinc blende structure has been widely studied; the various structural, electronic and optical properties of semiconductor materials adopting this structure are well illustrated and discussed in the literature. On the other side, these properties are poorly understood for WZ. Study of WZ III-V materials and related heterostructures is the subject of this work. In particular, I have simulated the structural and electronic properties of relaxed InAs and InP and under strain condition. ab initio modeling or first principle may explore structural, electronic and dynamics of matter without any experimental prior knowledge. Here, DFT calculations are performed to model the structural and electronic properties of WZ InAs and InP. The error in the evaluation of conduction energy states has been circumvented with the use of GW approximation and hybrid functionals. Finally, I have studied band offset alignment and polarizations effects in InAs/InP WZ system.

The aggressive reduction of feature size in silicon (Si)-based complimentary metal-oxide-semiconductor (CMOS) technology has resulted in an exponential increase in computing power. Stemming from increases in device density and substantial progress in materials science and transistor design, the integrated circuit has seen continual performance improvements and simultaneous reductions in operating power (VDD). Nevertheless, existing Si-based metal-oxide-semiconductor field-effect transistors (MOSFETs) are rapidly approaching the physical limits of their scaling potential. New material innovations, such as binary group IV or ternary III-V compound semiconductors, and novel device architectures, such as the tunnel field-effect transistor (TFET), are projected to continue transistor miniaturization beyond the Si CMOS era. Unlike conventional MOSFET technology, TFETs operate on the band-to-band tunneling injection of carriers from source to channel, thereby resulting in steep switching characteristics. Furthermore, narrow bandgap semiconductors, such as germanium (Ge) and InxGa1-xAs, enhance the ON-state current and improve the switching behavior of TFET devices, thus making these materials attractive candidates for further study. Moreover, epitaxial growth of Ge on InxGa1-xAs results in tensile stress (ε) within the Ge thin-film, thereby giving device engineers the ability to tune its material properties (e.g., mobility, bandgap) via strain engineering and in so doing enhance device performance. For these reasons, this research systematically investigates the material, optical, electronic transport, and heterointerfacial properties of ε-Ge/InxGa1-xAs heterostructures grown on GaAs and Si substrates. Additionally, the influence of strain on MOS interfaces with Ge is examined, with specific application toward low-defect density ε-Ge MOS device design. Finally, vertical ε-Ge/InxGa1-xAs tunneling junctions are fabricated and characterized for the first time, demonstrating their viability for the continued development of next-generation low-power nanoelectronic devices utilizing the Ge/InxGa1-xAs material system. / Doctor of Philosophy / The aggressive scaling of transistor size in silicon-based complimentary metal-oxide-semiconductor technology has resulted in an exponential increase in integrated circuit (IC) computing power. Simultaneously, advances in materials science, transistor design, IC architecture, and microelectronics fabrication technologies have resulted in reduced IC operating power requirements. As a consequence, state-of-the-art microelectronic devices have computational capabilities exceeding those of the earliest super computers at a fraction of the demand in energy. Moreover, the low-cost, high-volume manufacturing of these microelectronic devices has resulted in their nigh-ubiquitous proliferation throughout all aspects of modern life. From social engagement to supply chain logistics, a vast web of interconnected microelectronic devices (i.e., the "Internet of Things") forms the information technology bedrock upon which 21st century society has been built. Hence, as progress in microelectronics and related fields continues to evolve, so too does their impact on an increasingly dependent world. Moore's Law, or the doubling of IC transistor density every two years, is the colloquialism used to describe the rapid advancement of the microelectronics industry over the past five decades. As mentioned earlier, parallel improvements in semiconductor technologies have spearheaded great technological change. Nevertheless, Moore's Law is rapidly approaching the physical limits of transistor scaling. Consequently, in order to continue improving IC (and therefore microelectronic device) performance, new innovations in materials and fabrication science, and transistor and IC designs are required. To that end, this research systematically investigates the material, optical, and electrical properties of novel semiconductor material systems combining elemental (e.g., Germanium) and compound (e.g., Gallium Arsenide) semiconductors. Additionally, alternative transistor design concepts are explored that leverage the unique properties of the aforementioned materials, with specific application to low-power microelectronics. Therefore, through a holistic approach towards semiconductor materials, devices, and circuit co-design, this work demonstrates, for the first time, novel transistor architectures suitable for the continued development of next-generation low-power, high-performance microelectronic devices.

<p>The traditional semiconductor device scaling based on Moore’s law is reaching its physical limits. New materials hosting rich physical phenomena such as correlated electronic behavior may be essential to identify novel approaches for information processing. The tunable band structures in such systems enables the design of hardware for neuromorphic computing. Strongly correlated perovskite nickelates (ReNiO3) represent a class of quantum materials that possess exotic electronic properties such as metal-to-insulator transitions. In this thesis, detailed studies of NdNiO3 thin films from wafer-scale synthesis to structure characterization and to electronic device demonstration will be discussed.</p> <p>Atomic layer deposition (ALD) of correlated oxide thin films is essential for emerging electronic technologies and industry. We reported the scalable ALD growth of neodymium nickelate (NdNiO3) with high crystal quality using Nd(iPrCp)3, Ni(tBu2-amd)2 and ozone (O3) as precursors. By controlling various growth parameters such as precursor dose time and reactor temperature, we have optimized ALD condition for perovskite phase of NdNiO3­. We studied the structure and electrical properties of ALD NdNiO3 films epitaxially grown on LaAlO3 and confirmed their properties were comparable to those synthesized by physical vapor deposition methods. </p> <p>ReNiO3 undergoes a dramatic phase transition by hydrogen doping with catalytic electrodes independent of temperature. The electrons from hydrogen occupy Ni 3<em>d</em> orbitals and create strongly correlated insulating state with resistance changes up to eight orders of magnitudes. At room temperature, protons remain in the lattice locally near catalytic electrodes and can move by electrical fields due to its charge. The effect of high-speed voltage pulses on the migration of protons in NdNiO3 devices is discussed. After voltage pulses were applied with changing the voltage magnitude in nanosecond time scale, the resistance changes of the nickelate device were investigated. </p> <p>Reconfigurable perovskite nickelate devices were demonstrated and a single device can switch between multiple electronic functions such as neuron, synapse, resistor, and capacitor controlled by a single electrical pulse. Raman spectroscopy showed that differences in local proton distributions near the Pd electrode leads to different functions. This body of results motivates the search for novel materials where subtle compositional or structural differences can enable different gaps that can host neuromorphic functions.</p>

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.

Title from PDF of title page. / Document formatted into pages; contains 64 pages. / Thesis (M.E.E.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: The ability of Mercuric Iodide (HgI2) to function as a highly efficient radiation detector at room temperature has generated great interest and has triggered further studies on this difficult material. This property is expected to enable significant enhancements to a far-ranging variety of applications and systems. HgI2 devices have shown superior performance at room temperature compared to elemental Si or Ge devices, which require to be cooled down to liquid nitrogen temperature when used as nuclear radiation detectors. While substantial studies have been conducted on single crystal HgI2, polycrystalline HgI2 remains a comparatively less studied form of this material. The primary use of HgI2 is as a direct radiation detector. It can also be used in applications with a scintillator intermediate to generate visible light from incident nuclear radiation. Hence its response to visible light can be used to study the electronic properties of HgI2 polycrystalline films. / ABSTRACT: The films are deposited on TEC-15 LOF glass with a Tin Oxide(Sn02) coating which acts as the growth surface. It also acts as the front contact with Palladium (Pd) being the back contact. Wire leads are attached to the palladium for electrical contact. The deposited films are circular in shape with a diameter of 2.5cm with thickness ranging from 50 to 600ìm. A maximum of 7 devices are contacted at various points on every film. For the measurements documented in this thesis, a tungsten-halogen lamp and an Oriel 1/4m grating monochromator are used as a light source. The incident flux on the sample is determined using a Si photodiode as reference. Device performance for both single crystal as well as polycrystalline films is documented. We have attempted to identify a set of optimum growth parameters using these measurements. / ABSTRACT: For a film to be considered favorably, not only should the individual devices show high quantum efficiencies and low dark currents, but the response of all devices on the same film should be uniform. A number of films are studied and the optimum film deposition conditions are commented upon. A powerful semiconductor device simulation tool, MEDICItm, is used to simulate the photoresponse of these films. The simulations are compared to the measurements and the transport and light absorption parameters of the polycrystalline films are determined. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

The progress in device performance of modern microelectronic technology is mainly driven by down-scaling. In the near future, this road will probably reach a point where physical limits make even more down-scaling impossible. The substitution of single components materialwise over the last decades, like high-k dielectrics or metal gates, has been a suitable approach to foster performance improvements. In this scheme, the integration of high-mobility III-V compound semiconductors as channel materials into Si technology is a promising route to follow for the next one or two device generations. III-V integration, today, is conventionally performed by using techniques like molecular beam epitaxy or wafer bonding which utilize solid phase crystallization but suffer to strain due to the lattice mismatch between III-V compounds and Si. An alternative approach using sequential ion beam implantation in combination with a subsequent flash lamp annealing is presented in this work. Using this technique, nanocrystals from various III-V compounds have been successfully integrated into bulk Si and Ge as well as into thin Si layers which used either SOI substrates or were grown by plasma-enhanced chemical vapour deposition. The III-V compounds which have been fabricated are GaP, GaAs, GaSb, InP, InAs, GaSb and InxGa1-xAs with variable composition. The structural properties of these nanocrystals have been investigated by Rutherford backscattering, scanning electron microscopy and transmission electron microscopy, including bright-field, dark-field, high-resolution, high-angle annular dark-field and scanning mode imaging, electron-dispersive x-ray spectroscopy and energy-filtered element mapping. Furthermore, Raman spectroscopy and X-ray diffraction have been performed to characterise the nanocrystals optically. In Raman spectroscopy, the characteristic transversal and longitudinal optical phonon modes of the different III-V compounds have been observed. These signals proof that the nanocrystals have formed by the combination of ion implantation and flash lamp annealing. Additionally, the appearance of the typical phonon modes of the respective substrate materials verifies recrystallization of the substrate by the flash lamp after amorphisation during implantation. In the bulk Si samples, the nanocrystals have a circular or rectangular lateral shape and they are randomly distributed at the surface. Their cross-section has either a hemispherical or triangular shape. In bulk Ge, there are two types of precipitates: one at the surface with arbitrary shape and another one buried with circular shape. For the thin film samples, the lateral shape of the nanocrystals is more or less arbitrary and they feature a block-like cross-section which is limited in height by the Si layer thickness. Regarding crystalline quality, the nanocrystals in all samples are mainly single-crystalline with only a few number of stacking faults. However, the crystalline quality in the bulk samples is slightly better than in the thin films. The X-ray diffraction measurements display the (111), (220) and (311) Bragg peaks for InAs and GaAs as well as for the InxGa1-xAs where the peaks shift with increasing In content from GaAs towards InAs. The underlying formation mechanism is identified as liquid phase epitaxy. Hereby, the ion implantation leads to an amorphisation of the substrate material which is then molten by the subsequent flash lamp annealing. This yields a homogeneous distribution of the implanted elements within the melt due to their strongly increased diffusivity in the liquid phase. Afterwards, the substrate material starts to recrystallize at first and an enrichment of the melt with group-III and group-V elements takes place due to segregation. When the temperature is low enough, the III-V compound semiconductor starts to crystallize using the recrystallized substrate material as a template for epitaxial growth. In order to gain control over the lateral nanocrystal distribution, an implantation mask of either aluminium or nickel is introduced. Using this mask, only small areas of the samples are implanted. After flash lamp treatment, nanocrystals form only in these small areas, which allows precise positioning of them. An optimal implantation window size with an edge length of around 300nm has been determined to obtain one nanocrystal per implanted area. During an additional experiment, the preparation of Si nanowires using electron beam lithography and reactive ion etching has been conducted. Hereby, two different processes have been investigated; one using a ZEP resist, a lift-off step and a Ni hard mask and another one using a hydrogen silsesquioxane resist which is used directly as a mask for etching. The HSQ-based process turned out to yield Si nanowires of better quality. Combining both, the masked implantation and the Si nanowire fabrication, it might be possible to integrate a single III-V nanocrystal into a Si nanowire to produce a III-V-in-Si-nanowire structure for electrical testing. / Der Fortschritt in der Leistungsfähigkeit der Bauelemente moderner Mikroelektroniktechnologie wird hauptsächlich durch das Skalieren vorangetrieben. In naher Zukunft wird dieser Weg wahrscheinlich einen Punkt erreichen, an dem physikalische Grenzen weiteres Herunterskalieren unmöglich machen. Der Austausch einzelner Teile auf Materialebene, wie Hoch-Epsilon-Dielektrika oder Metall-Gate-Elektroden, war während der letzten Jahrzehnte ein geeigneter Ansatz, um die Leistungsverbesserung voranzubringen. Nach diesem Schema ist die Integration von III-V-Verbindungshalbleiter mit hoher Mobilität ein vielversprechender Weg, dem man für die nächsten ein oder zwei Bauelementgenerationen folgen kann. Heutzutage erfolgt die III-V-Integration konventionell mit Verfahren wie der Molekularstrahlepitaxie oder dem Waferbonden, welche die Festphasenkristallisation nutzen, die aber aufgrund der Gitterfehlanpassung zwischen III-V-Verbindungen und Silizium an Verspannungen leiden. In dieser Arbeit wird ein alternativer Ansatz präsentiert, welcher die sequenzielle Ionenstrahlimplantation in Verbindung mit einer darauffolgenden Blitzlampentemperung ausnutzt. Mit Hilfe dieses Verfahrens wurden Nanokristalle verschiedener III-V-Verbindungshalbleiter erfolgreich in Bulksilizium- und -germaniumsubstrate sowie in dünne Siliziumschichten integriert. Für die dünnen Schichten wurden hierbei entweder SOI-Substrate verwendet oder sie wurden mittels plasmagestützer chemischer Gasphasenabscheidung gewachsen. Die hergestellten III-V-Verbindungen umfassen GaP, GaAs, GaSb, InP, InAs, InSb und InxGa1-xAs mit veränderbarer Zusammensetzung. Die strukturellen Eigenschaften dieser Nanokristalle wurden mit Rutherford-Rückstreu-Spektroskopie, Rasterelektronenmikroskopie und Transmissionselektronenmikroskopie untersucht. Bei der Transmissionelektronenmikroskopie wurden die Hellfeld-, Dunkelfeld-, hochauflösenden, “high-angle annular dark-field” und Rasteraufnahmemodi sowie die energiedispersive Röntgenspektroskopie und die energiegefilterte Elementabbildung eingesetzt. Darüber hinaus wurden Ramanspektroskopie- und Röntgenbeugungsmessungen durchgeführt, um die Nanokristalle optisch zu charakterisieren. Mittels Ramanspektroskopie wurden die charakteristischen transversal- und longitudinal-optischen Phononenmoden der verschiedenen III-V-Verbindungen beobachtet. Diese Signale beweisen, dass sich unter Verwendung der Kombination von Ionenstrahlimplantation und Blitzlampentemperung Nanokristalle bilden. Weiterhin zeigt das Vorhandensein der typischen Phononenmoden der jeweiligen Substratmaterialien, dass die Substrate aufgrund der Blitzlampentemperung rekristallisiert sind, nachdem sie durch Ionenimplantation amorphisiert wurden. In den Bulksiliziumproben besitzen die Nanokristalle eine kreisförmige oder rechteckige Kontur und sind in zufälliger Anordnung an der Oberfläche verteilt. Ihr Querschnitt zeigt entweder eine Halbkugel- oder dreieckige Form. Im Bulkgermanium gibt es zwei Arten von Ausscheidungen: eine mit willkürlicher Form an der Oberfläche und eine andere, vergrabene mit sphärischer Form. Betrachtet man die Proben mit den dünnen Schichten, ist die laterale Form der Nanokristalle mehr oder weniger willkürlich und sie zeigen einen blockähnlichen Querschnitt, welcher in der Höhe durch die Siliziumschichtdicke begrenzt ist. Bezüglich der Kristallqualität sind die Nanokristalle in allen Proben mehrheitlich einkristallin und weisen nur eine geringe Anzahl an Stapelfehlern auf. Jedoch ist die Kristallqualität in den Bulkmaterialien ein wenig besser als in den dünnen Schichten. Die Röntgenbeugungsmessungen zeigen die (111), (220) und (311) Bragg-Reflexe des InAs und GaAs sowie des InxGa1-xAs, wobei sich hier die Signalpositionen mit steigendem Gehalt an Indium von GaAs zu InAs verschieben. Als zugrundeliegender Bildungsmechanismus wurde die Flüssigphasenepitaxie identifiziert. Hierbei führt die Ionenstrahlimplantation zu einer Amorphisierung des Substratmaterials, welches dann durch die anschließende Blitzlampentemperung aufgeschmolzen wird. Daraus resultiert eine homogene Verteilung der implantierten Elemente in der Schmelze, da diese eine stark erhöhte Diffusivität in der flüssigen Phase aufweisen. Danach beginnt zuerst das Substratmaterial zu rekristallisieren und es kommt aufgrund von Segregationseffekten zu einer Anreicherung der Schmelze mit den Gruppe-III- und Gruppe-V-Elementen. Wenn die Temperatur niedrig genug ist, beginnt auch der III-V-Verbindungshalbleiter zu kristallisieren, wobei er das rekristallisierte Substratmaterial als Grundlage für ein epitaktisches Wachstum nutzt. In der Absicht Kontrolle über die laterale Verteilung der Nanokristalle zu erhalten, wurde eine Implantationsmaske aus Aluminium beziehungsweise Nickel eingeführt. Durch die Benutzung einer solchen Maske wurden nur kleine Bereiche der Proben implantiert. Nach der Blitzlampentemperung werden nur in diesen kleinen Bereichen Nanokristalle gebildet, was eine genaue Positionierung dieser erlaubt. Es wurde eine optimale Implantationsfenstergröße mit einer Kantenlänge von ungefähr 300 nm ermittelt, damit sich nur ein Nanokristall pro implantierten Bereich bildet. Während eines zusätzlichen Experiments wurde die Präparation von Siliziumnanodrähten mit Hilfe von Elektronenstrahllithografie und reaktivem Ionenätzen durchgeführt. Hierbei wurden zwei verschiedene Prozesse getestet: einer, welcher einen ZEP-Lack, einen Lift-off-Schritt und eine Nickelhartmaske nutzt, und ein anderer, welcher einen HSQ-Lack verwendet, der wiederum direkt als Maske für die Ätzung dient. Es stellte sich heraus, dass der HSQ-basierte Prozess Siliziumnanodrähte von höherer Qualität liefert. Kombiniert man beides, die maskierte Implantation und die Siliziumnanodrahtherstellung, miteinander, sollte es möglich sein, einzelne III-V-Nanokristalle in einen Siliziumnanodraht zu integrieren, um eine III-V-in-Siliziumnanodrahtstruktur zu fertigen, welche für elektrische Messungen geeignet ist.