<p>As  thefundamentallimits  of  two-dimensional(2D)geometric  scaling  of  commercial transistors  are  being reached,  there  is  tremendous  demand  for  new  materials  and  process innovations  that  can  keep  delivering  performance  improvements  for  future  generations  of computing chips. One major avenue being explored istheincorporation ofan increasing degree of three-dimensionality   by   vertically   stacking   logic   and   memory   layerswith   high-density interconnections.In  this  dissertation,  high-performanceultra-thin  amorphousindium  oxide transistors  are  demonstrated as  an  excellent  candidate  for these  back-end-of-line  (BEOL)  and monolithic 3D (M3D) integration applications.</p> <p>A  major  pain-point  in the  development  of  BEOL  and  M3D  systems is  the  strict  thermal budget imposed –once the bottom layer of devices is fabricated, they can generally withstand no more  than  400 °C.  It  is  exceedingly  difficult  to  directly  deposit  single-crystal  material  at  these temperatures, and polycrystalline materials will have grain boundary instability issues. Amorphous materials  generally  have  low  carrier  mobilities,  which  would  seemingly  remove  them  from contention as well. Indium oxideand itsclass of related metal oxides are exceptions. Indium oxideis  a  wide  bandgap  semiconductor  with  high  electron  mobility  up  to  about  100  cm²/V∙s  in amorphous form. Ithas a strong preference for native degenerate n-type doping which has hindered prior  devices  fabricated  with it.  In  this  dissertation,  extremely  thin  layers  on  the  order  of  1  nm thick are used for which quantum confinement effects widen the bandgap further, reliably enabling gate-controllable  carrier  densitiesand  demonstration  of  excellent  transistor  performance  with  a low thermal budget of just 225 °C.</p> <p>Detailed characterization is performed down to 40 nm channel lengths revealing excellent transistor characteristics  includingenhancement-mode operation withon currents greater than 2 A/μm, low  subthreshold  swing,and  high  on/off  ratios  due  to  the  wide  bandgap.  Subsequent chaptersdemonstrate the fundamental lower limits of off current around 6 ×10^-20A/μmby a novel measurement  technique,  good  gate  bias  stress  stability  behaviorwith  small  parameter  drift  at silicon  complementary  metal  oxide  semiconductor  (CMOS)  logic  voltages,  and  high-frequency operationin the GHz regime enabling easy operation at CMOS clock frequencies.</p>

This dissertation work is a study of the growth kinematics, synthesis strategies and intrinsic properties of InSb nanowires (NWs). The highlights of this work include a study of the effect of the growth parameters on the composition and crystallinity of NWs. A change in the temperature ramp-up rate as the substrate was heated to reach the NW growth temperature resulted in NWs that were either crystalline or amorphous. The as-grown NWs were found to have very different optical and electrical properties. The growth mechanism for crystalline NWs is the standard vapor-liquid-solid growth mechanism. This work proposes two possible growth mechanisms for amorphous NWs. The amorphous InSb NWs were found to be very sensitive to laser radiation and to heat treatment. Raman spectroscopy measurements on these NWs showed that intense laser light induced localized crystallization, most likely due to radiation induced annealing of defects in the region hit by the laser beam. Electron transport measurements revealed non-linear current-voltage characteristics that could not be explained by a Schottky diode behavior. Analysis of the experimental data showed that electrical conduction in this material is governed by space charge limited current (SCLC) in the high bias-field region and by Ohm's law in the low bias region. Temperature dependent conductivity measurements on these NWs revealed that conduction follows Mott variable range hopping mechanism at low temperatures and near neighbor hopping mechanism at high temperature. Low-temperature annealing of the amorphous NWs in an inert environment was found to induce a phase transformation of the NWs, causing their crystallinity to be enhanced. This thesis also proposes a new and low-cost strategy to grow p-type InSb NWs on InSb films grown on glass substrate. The high quality polycrystalline InSb film was used as the host on which the NWs were grown. The NWs with an average diameter of 150 nm and length of 20 μm were shown to have hole concentration of about 1017 cm-3 and mobility of about 1000 cm2V-1s-1. This thesis also proposes a strategy for the fabrication of metal-semiconductor nanocomposites. InSb NWs grown by electrochemical deposition were decorated with nanometer sized Au and Ag nanoparticles to form the nanocomposite.

No description available.

The author presents the successful development of an on-chip, monolithic, integrated rubidium vapor-cell. These vapor-cells integrate ridge waveguide techniques with hollow-core waveguiding technology known as Anti-Resonant Reflecting Optical Waveguides (ARROWs). These devices are manufactured on-site in BYU's Integrated Microelectronic Laboratory (IML) using common silicon wafer microfabrication techniques. The ARROW platform fabrication is outlined, but the bulk of the dissertation focuses on novel packaging techniques that allow for the successful introduction and sealing of rubidium vapor into these micro-sized vapor-cells. The unique geometries and materials utilized in the ARROW platform render common vapor-cell sealing techniques unusable. The development of three generations of successful vapor-cells is chronicled. The sealing techniques represented in these three generations of vapor-cells include high-temperature epoxy seals, cold-weld copper crimping, variable pressure vacuum capabilities, indium solder seals, and electroplated passivation coatings. The performance of these seals are quantified using accelerated lifetime tests combined with optical spectroscopy. Finally, the successful probing of the rubidium absorption spectrum, electromagnetically induced transparency, and slow light on the ARROW-based vapor-cell platform is reported.

Photonic switches are becoming key components in advanced optical networks because of the large variety of applications that they can perform. One of the key advantages of photonic switches is that they redirect or convert light without having to make any optical to electronic conversions and vice versa, thus allowing networking functions to be lowered into the optical layer. InP-based switches are particularly attractive because of their small size, low electrical power consumption, and compatibility with integration of laser sources, photo-detectors, and electronic components. In this dissertation the development of integrated InP photonic switches using an area-selective zinc diffusion process has been investigated. The zinc diffusion process is implemented using a semi-sealed open-tube diffusion technique. The process has proven to be highly controllable and reproducible by carefully monitoring of the diffusion parameters. Using this technique, isolated p-n junctions exhibiting good I-V characteristics and breakdown voltages greater than 10 V can be selectively defined across a semiconductor wafer. A series of Mach-Zehnder interferometric (MZI) switches/modulators have been designed and fabricated. Monolithic integration of 1x2 and 2x2 MZI switches has been demonstrated. The diffusion process circumvents the need for isolation trenches, and hence optical losses can be significantly reduced. An efficient optical beam steering device based on InGaAsP multiple quantum wells is also demonstrated. The degree of lateral current spreading is easily regulated by controlling the zinc depth, allowing optimization of the injected currents. Beam steering over a 21 microns lateral distance with electrical current values as low as 12.5 mA are demonstrated. Using this principle, a reconfigurable 1x3 switch has been implemented with crosstalk levels better than -17 dB over a 50 nm wavelength range. At these low electrical current levels, uncooled and d.c. bias operation is made feasible. The use of multimode interference (MMI) structures as active devices have also been investigated. These devices operate by selective refractive index perturbation on very specific areas within the MMI structure, and this is again realized using zinc diffusion. Several variants such as a compact MMI modulator that is as short as 350 µm, a robust 2x2 photonic switch and a tunable MMI coupler have been demonstrated.

The increasing energy demand, combined with the use of harmful non-renewable energy sources calls for the search of alternative methods to cover our energy need.Renewable energy can be harvested in different ways, through the movement of wind and water, biomass, or directly from the rays of the sun, as in the case of photovoltaic (PV) devices. Whilst crystalline silicon (c-Si) is the most common absorber used for solar cells, other technologies are emerging. Solar cells with copper indium gallium diselenide (CIGS) as an absorber have the possibility of being flexible, which is an advantage due to the many more application possibilities that appear compared to the rigid and heavy c-Si solar cells. CIGS solar cells have some long-term stability issues, especially regarding ingression of atmospheric species through the front contact layer. This calls for further research in the front contact of the CIGS solar cell, exploring alternative materials to prevent degradation. The front contact of a solar cell must be both optically transparent and conduct electricity. Transparent conductive oxides (TCO) are materials characterized by the ability to conduct electricity, while also possessing a certain degree of optical transparency. The combination of conductivity and transparency makes TCOs ideal as front contacts in solar cells. A very common TCO for front contacts in CIGS solar cells is aluminum-doped zinc oxide (AZO) due to its low cost, good electrical conductivity and optical transparency. Because of its low resistance to degradation in humid environments more robust TCO alternatives, such as indium-doped tin oxide (ITO), are being investigated. Indium-doped tin oxide possesses similar electrical and optical properties as AZO, but better stability in humid environments.The ITO was deposited through RF magnetron sputtering, on a glass substrate to be able to measure optical properties. Initially, experiments focusing on oxygen content in the deposition atmosphere were done, together with a reproducibility experiment. This gave useful information about sputtering parameters and stability of the deposition. Thereon, an experiment was done varying three parameters: oxygen content in deposition atmosphere, sputtering power and temperature of substrate. A statistical software was used to analyze the data, identifying the effects of the changing parameters. The best performing samples were made with an oxygen content of 0,4-0,6 vol%. A high sensibility for oxygen in the system was also observed, as a result of the initial reproducibility experiments. This led to the introduction of a sacrificial deposition step after the machine had been shut down. Optimal substrate temperature was around 150°Cand it was not possible to go higher due to sensibility of the underlying solar cell layers.A lower threshold for the film thickness, located somewhere between 125 and 175 nm, was observed. Films with thickness below this threshold experienced a large resistivityincrease. Further depositions with higher oxygen content are advised to see if the properties of the films further improve.

No description available.

No description available.

Ionic liquids (ILs) are able to activate elements that are insoluble in common solvents. Here, the synthesis of binary antimony compounds directly from elements was explored. The 12 elements Ti-Cu, Al, Ga, In, and Te, known to form binary compounds with Sb, were reacted with Sb in [P₆₆₆₁₄]Cl under inert conditions in a closed glass flask with vigorous stirring for 16 h at 200 °C. This was immediately successful in four cases and resulted in the formation of NiSb, InSb, Cu₂Sb and Sb₂Te3. The applied reaction temperature is several hundred degrees below the temperatures required for solvent-free conversions. Compared to reactions based on diffusion in the solid state, reaction times are much shorter. The IL is not consumed and can be recycled. Since the reaction with Cu showed almost complete conversion, the influences of reaction time, temperature and medium were further investigated. Among the tested imidazolium ILs ([BMIm]Cl, [BMIm][OAc], [BDMIm]Cl) and phosphonium ILs ([P₆₆₆₁₄]X, X=Cl⁻, [DCA]⁻, [OAc]⁻, [NTf₂]⁻), those with chloride anion yielded the best results. In a diffusion experiment, Cu₂Sb formed on the copper, which indicates that antimony forms mobile species in these ILs. Supplemental crystal structure data of (As₃S₄)[AlCl₄], which was ionothermally synthesized from As and S, are reported.

Tesis por compendio / [ES] Los sesquicalcogenuros con estequiometria B2X3, con A = Al, Ga e In y X = S, Se y Te, han recibido gran atención a lo largo de los últimos años, en particular en como modificarlos para obtener nuevas estructuras con propiedades inéditas, permitiendo su uso en una amplia variedad de aplicaciones. Si bien vías como el uso de altas/bajas temperaturas o modificar la composición química han sido bastante explotadas para modificar y obtener nuevas estructuras, las altas presiones están ganando auge como una tercera vía para obtener nuevos materiales. El uso de altas presiones implica emplear celdas de yunques de diamantes, preparadas para alcanzar altas presiones, además de altas temperaturas. A estos dispositivos se acoplan multitud de técnicas experimentales, como espectroscópicas (Raman e IR), difracción y absorción de rayos X, medidas de absorción óptica, de resistividad, etc., con el fin de estudiar como la materia evoluciona en dichas condiciones extremas. Adicionalmente, los cálculos teóricos son empleados como apoyo a los resultados experimentales. Dentro de los trabajos existentes a altas presiones de esta familia de compuestos, estos han llegado a conclusiones incluso contradictorias, arrojando más dudas acerca su comportamiento bajo presión. De todos los integrantes de estos sesquicalcogenuros, Ga2S3, In2S3 y In2Se3, han sido los más estudiados bajo presión. En esta tesis se han evaluado los efectos de la alta presión en estos tres sesquicalcogenuros, haciendo uso de espectroscopia Raman y difracción de rayos X, siempre con el soporte de los cálculos teóricos, con el fin de aclarar los resultados publicados anteriormente. Fruto de estos trabajos, la presente tesis recoge los cuatro artículos publicados en revistas indexadas. Dichos artículos han dado luz al comportamiento bajo presión de estos compuestos, como caracterización de propiedades vibracionales y estructurales bajo presión, mecanismos de transición, transiciones de fase inducidas bajo presión, así como caracterizar dichas fases de alta presión. Con todo ello, estos trabajos pretenden no solo conocer fehacientemente el comportamiento bajo presión de estos tres sesquicalcogenuros, sino impulsar futuros trabajos en el resto de los compuestos de esta familia y en otros similares, como en compuestos ternario AB2X4 con estructura tipo espinela y vacantes ordenadas. / [CA] Els sesquicalcogenurs amb estequiometria B2X3, amb B = Al, Ga, i In i X = S, Se, i Te, han rebut una gran atenció al llarg dels darrers anys, en particular sobre com modificar-los per tal d'obtindre noves estructures amb propietats inédites, permetent el seu ús en una àmplia varietat d'aplicacions. Si bé l'ùs d'altes/baixes temperatures o modificar la composició química han segut prou explotades per a modificar i obtindre noves estructures, les altes pressions estan guanyant importància com una tercera via per a obtindrer nous materials. L'ús d'altes presions implica emprar cel·les d'encluses de diamants, preparades per a assolir altes presions, a més a més d'altes temperatures. A aquestos dispositius s'acoblen multitud de tècniques experimentals, com ara espectroscòpiques (Raman i IR), difracció i absorció de raigs X, mesures òptiques, de resistivitat, etc, amb la finalitat d'estudiar com la matèria evoluciona en aquestes condicions extremes. Adicionalment, els càlculs teòrics son emprats com a recolçament dels resultats experimentals. Dins dels treballs existents a altes presions a aquesta familia de compostos s'ha arribat a determinades conclusions algunes de les quals son contradictòries, el que ha sembrat moltes dubtes al voltant del seu comportament sota pressió. De tots els integrants d'aquestos sesquicalcogenurs, Ga2S3, In2S3 i In2Se3 han sigut els més estudiats sota pressió. En aquesta tesi doctoral s'han evaluat els efectes de les altes pressions a aquestos tres sesquicalcogenurs, fent ús de l'espectroscopia Raman i la difracció de raigs X, sempre amb el suport dels càlculs teòrics, amb el fi d'aclarir els resultats previament publicats. Fruit d'aquestos treballs, la present tesi doctoral recull els quatre articles publicats a revistes indexades. Aquestos articles han vessat llum sobre el comportament sota pressió d'aquestos compostos, com ara la caracterització de les seues propietats vibracionals i estructurals sota pressió, les transicions de fase induides sota pressió i els mecanismes d'eixes transicions, així com la caracterització de les seues fases d'alta pressió. Amb tot, aquestos treballs pretenen no només conèixer el comportament sota pressió d'aquestos tres sesquicalcogenurs, sino també impulsar futurs treballs a la resta de compostos d'aquesta familia i altres compostos rel·lacionats, com ara els compostos ternaris AB2X4 de tipus espinela i de vacants ordenades. / [EN] B2X3 sesquichalcogenides (A = Al, Ga and In, X = S, Se y Te) have received special attention along last years, with great emphasis in tailor them to attain new structures to novel properties, driving them in a huge number of applications. Although high/low temperature or varying chemical composition have been extensively used to modify and obtain new structures, high pressure is gaining relevance as an alternative way to synthetised new materials. To reach such pressures and additionally high/low temperatures, diamond anvil cells are used. Many experimental techniques can be coupled to these tools to study matter under extreme conditions (Raman and IR spectroscopy, X-ray diffraction and absorption, optical absorption, and resistivity measurements, among others). Additionally, computational simulations are used to give further support to the experimental results. Despite the several existing works devoted to the behaviour under pressure of this family, controversial results have been reported. The most studied of these sesquichalcogenides have been Ga2S3, In2S3 and In2Se3. The aim of this thesis is to revisit the pressure effects by means of Raman spectroscopy and X-ray diffraction, with the help of computational simulations, for the purpose of clarify the results published earlier. The current thesis contains the four articles published in indexed journals, resulting from the study of these three sesquichalcogenides. Such articles shed light to the pressure behavior of these compounds, their vibrational and structural properties under pressure, pressure-induced phase transitions and the mechanisms behind them and characterize such high-pressure phases. With these works, we pursue not only a depth understanding of the pressure behavior of these sesquichalcogenides, but boost future high-pressure works on the rest of the family and other similar compounds, as AB2X4 with spinel structure and ordered vacancies. / The authors thank the financial support from Spanish Research Agency (AEI) under projects MALTA Consolider Team network (RED2018-102612-T) and projects MAT2015- 710, MAT2016-75586-C4-2/3-P, FIS2017-83295-P, PID2019-106383GB-41/42/43, and PGC2018-097520-A-100, as well as from Generalitat Valenciana under Project PROMETEO/2018/123 (EFIMAT). / Gallego Parra, S. (2022). Experimental and Theoretical Study of B2X3 Sesquichalcogenides under Extreme Conditions [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/191502 / Compendio