Design and characterisation of millimetre wave planar Gunn diodes and integrated circuits

Heterojunction planar Gunn devices were first demonstrated by Khalid et al in 2007. This new design of Gunn device, or transferred electron device, was based on the well-established material system of GaAs as the oscillation media. The design did not only breakthrough the frequency record of GaAs for conventional Gunn devices, but also has several advantages over conventional Gunn devices, such as the possibility of making multiple oscillators on a single chip and compatibility with monolithic integrated circuits. However, these devices faced the challenge of producing high enough RF power for practical applications and circuit technology for integration. This thesis describes systematic work on the design and characterisations of planar Gunn diodes and the associated millimetre-wave circuits for RF signal power enhancement. Focus has been put on improving the design of planar Gunn diodes and developing high performance integrated millimetre-wave circuits for combining multiple Gunn diodes. Improvement of device design has been proved to be one of the key methods to increase the signal power. By introducing additional δ-doping layers, electron concentration in the channel increases and better Gunn domain formation is achieved, therefore higher RF power and frequency are produced. Combining multiple channels in the vertical direction within devices is another effective way to increase the output signal power as well as DC-to-RF conversion efficiency. In addition, an alternative material system, i.e. In0.23Ga0.77As, has also been studied for this purpose. Planar passive components, such as resonators, couplers, low pass filters (LPFs), and power combiners with high performance over 100 GHz have been developed. These components can be smoothly integrated with planar Gunn diodes for compact planar Gunn oscillators, and therefore contribute to RF power enhancement. In addition, several new measurement techniques for characterising oscillators and passive devices have also been developed during this work and will be included in this thesis

High-speed MSM photomixers for spectroscopy applications

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Development of a solid state amplifier for the 3rd harmonic cavity for ALBA synchrotron light source

In Synchrotron Light Source facilities with high energy and low emittance electron beams different techniques for improving the quality of the synchrotron light for the users are applied. With this aim ALBA, the Spanish 3rd generation Synchrotron Light Source, is developing a 3rd Harmonic radiofrequency (RF) system as a system additional to the main RF system of the storage ring. This system will consist of four normal conducting active cavities at 1.5 GHz that will provide the required 1.1 MV accelerating voltage to the electron beam and will be fed by four 20 kW power transmitters. This power will be generated by modular Solid State Power Amplifiers (SSPAs) in a continuous wave mode at 1.5 GHz. On the basis of preliminary studies it has been decided that the architecture of each 20 kW power transmitter is a tree diagram made up of primary 1 kW SSPA modules connected in parallel in a combination array. The present PhD thesis is devoted to the design, building and evaluation of a prototype of the 1 kW SSPA module formed four 250 W primary power amplifier modules. Accordingly, all subsystems, namely input and output matching networks of the 250 W primary module, and a four-way power splitter, a four-way power combiner and a novel directivity compensated directional coupler for the non-invasive power monitoring of the 1 kW power amplifier were also designed and their prototypes were tested. A final evaluation of the combined 1 kW SSPA prototype module was successfully carried out and has shown good performance.En las instalaciones de tipo Fuentes de luz de sincrotrón de haz de electrones de alta energía y baja emitancia se aplican diferentes técnicas de mejora de la calidad de la luz de sincrotrón. Con este objetivo, el ALBA, la fuente española de luz de sincrotrón de la tercera generación, está desarrollando un sistema de radiofrecuencia (RF) de la 3ª Harmónica como un sistema adicional al sistema de RF principal del anillo de almacenamiento. Este sistema consistirá de cuatro cavidades activas de conductividad normal de frecuencia 1,5 GHz que suministrarán un voltaje acelerador de 1.1 MV necesario para el haz de electrones y que serán alimentadas por cuatro transmisores de potencia de 20 kW. Esta potencia será generada en modo de onda continua a frecuencia 1.5 GHz por amplificadores de potencia de estado sólido (APES) de estructura modular. A partir de unos estudios preliminares se ha decidido que la arquitectura de cada transmisor de potencia de 20 kW es de tipo diagrama de árbol que consiste de APES primarios de potencia 1 kW conectados en paralelo formando una matriz de combinación. El tema de la presente tesis es el diseño, la construcción y la caracterización de un prototipo del módulo de APES de potencia 1 kW formado por cuatro amplificadores primarios de 250 W de potencia. También, todos subsistemas, concretamente los circuitos de adaptación de entrada y de salida del módulo primario de 250 kW, así como un divisor de cuatro salidas, un combinador de cuatro entradas y un acoplador direccional con una nova solución de compensación de directividad para una monitorización no invasiva han sido diseñados y sus prototipos han sido testeados. La evaluación final de funcionamiento del APES de 1 kW de potencia ha sido realizada con éxito y ha demostrado su buen rendimiento.Postprint (published version

Development of a solid state amplifier for the 3rd harmonic cavity for ALBA synchrotron light source

In Synchrotron Light Source facilities with high energy and low emittance electron beams different techniques for improving the quality of the synchrotron light for the users are applied. With this aim ALBA, the Spanish 3rd generation Synchrotron Light Source, is developing a 3rd Harmonic radiofrequency (RF) system as a system additional to the main RF system of the storage ring. This system will consist of four normal conducting active cavities at 1.5 GHz that will provide the required 1.1 MV accelerating voltage to the electron beam and will be fed by four 20 kW power transmitters. This power will be generated by modular Solid State Power Amplifiers (SSPAs) in a continuous wave mode at 1.5 GHz. On the basis of preliminary studies it has been decided that the architecture of each 20 kW power transmitter is a tree diagram made up of primary 1 kW SSPA modules connected in parallel in a combination array. The present PhD thesis is devoted to the design, building and evaluation of a prototype of the 1 kW SSPA module formed four 250 W primary power amplifier modules. Accordingly, all subsystems, namely input and output matching networks of the 250 W primary module, and a four-way power splitter, a four-way power combiner and a novel directivity compensated directional coupler for the non-invasive power monitoring of the 1 kW power amplifier were also designed and their prototypes were tested. A final evaluation of the combined 1 kW SSPA prototype module was successfully carried out and has shown good performance.En las instalaciones de tipo Fuentes de luz de sincrotrón de haz de electrones de alta energía y baja emitancia se aplican diferentes técnicas de mejora de la calidad de la luz de sincrotrón. Con este objetivo, el ALBA, la fuente española de luz de sincrotrón de la tercera generación, está desarrollando un sistema de radiofrecuencia (RF) de la 3ª Harmónica como un sistema adicional al sistema de RF principal del anillo de almacenamiento. Este sistema consistirá de cuatro cavidades activas de conductividad normal de frecuencia 1,5 GHz que suministrarán un voltaje acelerador de 1.1 MV necesario para el haz de electrones y que serán alimentadas por cuatro transmisores de potencia de 20 kW. Esta potencia será generada en modo de onda continua a frecuencia 1.5 GHz por amplificadores de potencia de estado sólido (APES) de estructura modular. A partir de unos estudios preliminares se ha decidido que la arquitectura de cada transmisor de potencia de 20 kW es de tipo diagrama de árbol que consiste de APES primarios de potencia 1 kW conectados en paralelo formando una matriz de combinación. El tema de la presente tesis es el diseño, la construcción y la caracterización de un prototipo del módulo de APES de potencia 1 kW formado por cuatro amplificadores primarios de 250 W de potencia. También, todos subsistemas, concretamente los circuitos de adaptación de entrada y de salida del módulo primario de 250 kW, así como un divisor de cuatro salidas, un combinador de cuatro entradas y un acoplador direccional con una nova solución de compensación de directividad para una monitorización no invasiva han sido diseñados y sus prototipos han sido testeados. La evaluación final de funcionamiento del APES de 1 kW de potencia ha sido realizada con éxito y ha demostrado su buen rendimiento

Spintronics: Fundamentals and applications

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes from the published versio

Acousto-Electrically Driven Charge Carrier Dynamics in Metal Halide Perovskites: From Fundamental Studies to Sensor Applications

In recent research on solar cells that can surpass with the efficient conventional modules on the basis of silicon, ever more new materials are synthesized and tested. One class of these materials which is highly promising for the application in solar cells is in perovskite structure. After a few years of research it was already shown to reach efficiencies as high as commercial cells. This crystal structure can be formed with various different material combinations. This thesis focuses on the group of metal halide perovskites as they have very promising optoelectronic properties. Beside variations in the composition, structures with lower dimensionality have also gained more interest. Their very flexible and easy fabrication process paired with their very interesting and exceptionally good electronic properties makes them exciting objects to study. The high absorption and photoluminescence quantum yield in the perovskite nanostructures opens up a whole field of possible studies to conduct. This thesis deals with electrical characterizations and manipulations of the charge carrier dynamics in nanowires of metal halide perovskites. In order to investigate the mechanisms that happen during transport of electrons and holes in such small systems, the contact-free detection method of acousto-optoelectric spectroscopy via surface acoustic wave application is chosen. This method is especially helpful in the examination of these small structures because it lacks the necessity of precisely defining metal contacts on the sample. Instead, the electric field accompanying the mechanical wave is exploited to act upon the charge carriers in a quasi-static approach as the field is adapted to the velocity of the sound wave which is much slower than the speed of light in the medium. In this way the electrons and holes react to the wave and can follow its movement and thus, be transported. In CsPbI3 perovskite nanowires the effect on excitons, bound electron hole pairs, is observed. Time-resolved measurements show that both charge carriers have similar mobilities and that both are moved. The effect of the surface acoustic wave on an exciton can be described by two phenomena: a dissociation and a polarization of the quasi-particle. This is validated in this thesis by the application of a phenomenological model that mimics exactly those two processes. A subsequent numerical calculation of the drift and diffusion equations applied to the system reveals more insights into the dynamics that happen during the application of the surface acoustic wave and confirms that the mobilities of electrons and holes are indeed equal and can be quantified to around 3 cm2/Vs. Low temperature studies confirm the findings and provide a deeper understanding of the system. A final repetition of the time-resolved experiment on the perovskite structure CsPbBr3 corroborates the great influence of the exciton binding energy on the strength of the observed phenomena. Additionally, the easily bandgap-tunable nanowires are perfect sensing materials via the effect of photoconductivity. In a tapered transducer design, the spatially resolved detection of light absorption via the nanostructures is realized. Through the photo-induced charge carrier creation in material deposited in the travelling path, the transmission of a surface acoustic wave can be altered by the reciprocal impact of charge carriers and electric field. This is exploited in the construction of a wavelength and position resolved detector. In the measurements, the recorded absorption edge of several materials nicely reproduces optical absorption measurements and matches the energy of the photoluminescence of the nanowires. The addition of a perpendicular pair of surface acoustic wave transmitter and receiver enables a full two dimensional position detection. The switch from a simple delay line to a resonator-based design shows that the surface acoustic wave can even be used as a mass load detector with high sensitivity through the shifts in resonance frequency induced by the mass. Through the stiffness changes, this works even for rather light material and small amounts. Furthermore, this design is also capable of sensing the conductivity of deposited material analogously to the aforementioned system. As a proof of principle, the absorption edge of one exemplary material is presented for this chip as well, which coincides nicely with the previous investigations.In der aktuellen Forschung zu Solarzellen, die mit den effizienten Modulen aus industriellem Silizium mithalten können, werden immer mehr neue Materialien hergestellt und getestet. Eine sehr vielversprechende Klasse von solchen Materialien für den Einsatz in Solarzellen ist die der Perowskitstrukturen. Nach nur wenigen Jahren der Forschung konnten diese bereits die gleiche Effizienz erreichen wie kommerzielle Solarzellen. Die besondere Kristallstruktur kann mit vielfältigen Materialkombinationen erreicht werden. Diese Arbeit fokussiert sich dabei auf die Gruppe der Metall-Halogen-Perowskite. Neben den Variationen in der Zusammensetzung des Materials haben auch niederdimensionale Strukturen an Interesse gewonnen. Ihre Flexibiltät und einfache Herstellung gepaart mit ihren sehr interessanten und außergewöhnlich guten elektrischen Eigenschaften, machen sie zu einem spannenden Forschungsobjekt. Die hohe Absorptionsrate und die hohe Quantenausbeute in der Photolumineszenz eröffnen ein ganz neues Feld möglicher Studien. Diese Arbeit beschäftigt sich mit der elektronischen Charakterisierung und der Manipulation der Ladungsträger in Nanodrähten aus Metall-Halogen-Perowskit. Um die Mechanismen während des Ladungsträgertransportes in so kleinen Systemen untersuchen zu können, wurde die Methode der akusto-optoelektrischen Spektroskopie mithilfe von Oberflächenwellen gewählt. Diese Messmethode ist besonders dann hilfreich, wenn ultrakleine Strukturen untersucht werden sollen, da keine Metallkontakte hochpräzise auf der Probe aufgebracht werden müssen. Stattdessen wird das elektrische Feld, welches die mechanische Wellen auf einem piezoelektrischen Substrat begleitet, ausgenutzt, um die Ladungsträger zu beeinflussen. Dies geschieht quasi-statisch, da die Feldgeschwindigkeit an die Schallgeschwindigkeit der akustischen Welle angepasst ist und sich nicht mit der Lichtgeschwindigkeit im Substrat ausbreitet. Dadurch haben die Elektronen und Löcher genug Zeit auf das Feld zu reagieren und können der Bewegung der Welle folgen, wodurch ein Transport stattfindet. In den CsPbI3-Nanodrähten wird der Effekt der Wellen auf Exzitonen, gebundene Elektron-Loch-Paare, beobachtet. In zeitaufgelösten Messungen zeigt sich, dass beide Ladungsträger die gleiche Mobilität haben und beide von der Welle gleichermaßen bewegt werden. Der Effekt der Oberflächenwelle auf die Exzitonen kann durch zwei Phänomene beschrieben werden: die Aufspaltung und die Polarisation des Quasi-Teilchens. Das wird in der Arbeit durch die Anwendung eines phänomenologischen Models bestätigt, welches genau diese beiden Effekte modelliert. Eine numerische Simulation der Drift- und Diffusionsgleichungen, angewendet auf das zu untersuchende System, bringt tiefere Einblicke in die Dynamik der Ladungsträger innerhalb der Nanostruktur und bestätigt, dass die Mobilitäten von Elektronen und Löchern gleich sind und kann zudem deren Wert auf rund 3 cm2/Vs quantifizieren. Messungen bei tiefen Temperaturen untermauern die Ergebnisse und liefern ein tieferes Verständnis des Systems. Eine Wiederholung der zeitaufgelösten Messung an CsPbBr3-Nanodrähten bestätigt den großen Einfluss der Bindungsenergie der Exzitonen auf die Stärke des beobachteten Effekts. Neben der Untersuchung der Nanodrähte selbst, können diese durch ihre einfach anzupassende Bandlücke über ihre Photoleitfähigkeit auch als Sensormaterial dienen. In einem speziellen, konischen Design der Schallwandler kann eine ortsaufgelöste Detektion realisiert werden. Durch die photoinduzierte Ladungsträgerbildung in dem im Schallpfad deponierten Material kann die Übertragung einer akustischen Oberflächenwelle durch die wechselseitige Wirkung von Ladungsträgern und elektrischem Feld verändert werden. Dies wird bei der Konstruktion eines wellenlängen- und positionsaufgelösten Detektors genutzt. Während der Messungen bildet die aufgenommene Absorptionskante mehrerer Materialien optische Absorptionsmessungen gut nach und passt zur Photolumineszenz der Nanodrähte. Das Hinzufügen eines senkrechten Paares von akustischem Oberflächenwellen-Sender und -Empfänger ermöglicht eine vollständige zweidimensionale Positionserfassung. Der Wechsel von einer einfachen Verzögerungsstrecke zu einem resonatorbasierten Design zeigt, dass die SAW auch als Massendetektor mit hoher Empfindlichkeit eingesetzt werden kann, wobei die Masse Verschiebungen in der Resonanzfrequenz induziert. Durch die Steifigkeitsänderungen funktioniert dies auch bei eher leichtem Material und kleinen Mengen. Darüber hinaus ist diese Anordnung auch in der Lage, zusätzlich die Leitfähigkeit des abgeschiedenen Materials analog zum vorgenannten System zu detektieren. Als Proof-of-principle wird auch für diesen Chip die Absorptionskante eines exemplarischen Materials vorgestellt, die gut mit den bisherigen Studien übereinstimmt

Scalable designs and methods for heterogeneous electronic-photonic integrated circuitry

A set of semiconductor designs shown to be capable of facilitating scalable and reconfigurable layouts for electronic-photonic integrated circuitry is presented. Three emphases are established to outline and discuss the methods and advantages of merging stand-alone optical components into integrated heterogeneous systems, specifically for implementing optical sensing, efficient laser wavelength tuning, and III-V-on-Si semiconductor fabrication techniques together on a single platform. Considerations regarding the optical geometries and power efficiency of each design are reiterated to assure that each design is compatible with the goals of system-level integration in either biochemical point-of-use or telecommunications applications. These three approaches to scalable photonic designs are then investigated in their ability to offer dynamic controls of optical signals and their novel usage of heterogeneous material patterning. The optical sensing platform directly integrates multiple linear variable filters (LVFs) atop a CMOS image sensor for electronic controls of detecting a biochemical fluorescent or absorptive optical signal signature, enabling good wavelength resolution (3.77−6.08 nm) over a wide-band detection spectrum. Detection limits of 0.28 nM for Quantum Dot emitters and 32 ng/mL for near-infrared fluorescent dyes are found in this integrated design, providing comparable results in the compact optical platform to conventional laboratory spectrometers. The instrument is then extended in its usage by testing on point-of-use detection tests via discerning the concentration of free-chlorine in water colorimetrically. The tunable laser cavity design integrates together a GaN waveguide into a standard InGaAsP telecom (1550 nm) edge-emitting laser atop silicon, allowing for wide-band tuning via the strong anisotropic effects solved for in wurtzite GaN. A tuning parameter based off a refractive index variation, Δ, is found to be at |1.75∙10E−4|, based off the electro-optic effects in conjunction with an etched grating geometry designed directly into the coupled GaN waveguide, with the structure further extended into a Y-branch laser cavity to enable the Vernier effect for wideband tuning via mode-hopping. A separate GaN-based design, consisting of an RF signal modulator that launches a surface acoustic wave (SAW) into a cavity to produce a highly controllable refractive index variation, Δ, via the photo-elastic and photo-elastic effects, is found to produce a large tuning parameter of |1.84∙10E−3|. These effects are then described in their application to dynamically controllable effects for dense wavelength division multiplexing (DWDM) and how the underlying electronic platform enables this, providing advantages over larger footprint or less efficient designs. The fabrication techniques designed provide a method to enable bonding of III-V epitaxial wafers onto a silicon carrier wafer for large-scale processing before final bonding onto CMOS. A processing recipe takes bulk GaAs epitaxial structures and constructs a method for reversibly bonding and processing them on a silicon carrier wafer as III-V islands, ready for final large scale flip-chip bonding onto aligning CMOS features. Additional findings discuss the merits of various etch processes and techniques such that they are compatible to the heterogeneous III-V-on-Si patterning as laid out. The methods optimized allow for simultaneous, heterogeneous development of system-level device integration such that further processing can place various III-V devices side-by-side and process geometries in unison. Processing steps and their results are presented. The extension of this method to different III-V alloys beyond GaAs entirely is therefore considered for even larger-scale system design across photonic elements. Each set of findings presents both the relevant photonic device characteristics and also a method on how to intersect these devices with a paired CMOS electronic system on silicon, so that a single unified electronic-photonic schematic can be made. Accompanying these conclusions is a range of experimental work ranging from simulation studies, to full-scale integrable sensing designs and their testing, to detailed cleanroom-based fabrication processes for designing the system of III-V-on-Si patterns. A final set of conclusions relates the three tracks of research as being part of a common path forward in scalable photonics designs. Forecasts are then made on how the field of electronic-photonic integration and its applications utilized herein may yet evolve and potentially encompass findings or methodologies from this work

Carrier transport in high-speed photodetectors based on two-dimensional-gas

Monolithically integrated high-speed photodetectors are important components in fiber communications and optoelectronic integrated circuits (OEIC) with metal-semiconductor-metal (MSM) photodetectors (PD) being the device of choice due to the its high overall performance and technology compatibility with integrated circuits (IC). The speed of conventional top illuminated MSM-PD is limited by the transit time of photogenerated carriers. The concept of internal vertical field, developed in the MSM intrinsic absorption region by the two-dimensional-gas along the heterojunction, is proposed and implemented for the purpose of facilitating carrier transport, hence improving the transit time limitations. The time response of a two-dimensional-electron-gas (2-DEG) based photodetector suggests an enhanced electron transport but a long tail due to the slow holes. We have designed and fabricated two-dimensional-hole-gas (2-DHG) based MSM photodetector to investigate hole transport in the vertical field MSM photodetector. Simulation of charge carrier transport, verifies experimentally observed behavior, which manifests the enhanced hole transport benefit from the vertical field.In addition, the 2-DHG based MSM structure device shows excellent capacitance-voltage (C-V) characteristic making it an excellent candidate for applications in odd-order high frequency multipliers. The high Cmax/Cmin ratio of 113 and high sensitivity of 35 are one of the best results reported. In addition, optoelectronic measurements demonstrate the slope of the C-V relationship can be modulated by the intensity of the incident optical power. A model describing the source of the C-V results is proposed along with the simulation results verifying the observed C-V behavior. In order to produce a complete picture of charge transport and collection, we developed a program using Ensemble-Monte-Carlo (EMC) method incorporating the electron-electron scattering in the 2-DEG confined by AlGaAs/GaAs heterojunction. The result reveals an energy thermalization time of tens of femto-second in the 2-DEG, which suggest the 2D gas has the potential to collect the photogenerated carriers.Based on all previous experimental results and analysis, a 2-DEG/2-DHG combined structure has been proposed on GaAs substrate. The design, taking advantage of the vertical field and fast thermalization time in the confined 2D gas, results in a wide bandwidth, high external quantum efficiency for vertically illuminated MSM device.Ph.D., Electrical Engineering -- Drexel University, 200

Solution Processable PbS QD-solid Photodetectors for telecommunication application

La detección óptica y la conversión de luz en electricidad (conversión fotovoltaica), en la que los dispositivos optoelectrónicos encuentran su campo de aplicación más importante, han sido importantes campo de aplicación durante décadas de los semiconductores monocristalinos como materiales fotoactivos (absorción de luz y fotogeneración de portadores). Su éxito se debe a los excelentes resultados alcanzados, aunque viene acompañado de inconvenientes, como el elevado coste de producción, la complejidad de fabricación y su incompatibilidad con substratos flexibles. Durante la última década, el advenimiento de los materiales optoelectrónicos procesados en disolución, como los puntos cuánticos (QDs) coloidales, ha abierto nuevas posibilidades para aplicaciones optoelectrónicas. Este nuevo enfoque aplicado al desarrollo de detectores ópticos reside en el alto grado de control que ofrece la ingeniería de materiales a la nanoescala. Además, la procesabilidad de dichos nanomateriales ha permitido su integración en muchos tipos de substratos comerciales de bajo coste, en algunos casos logrando fotodispositivos con figuras de mérito comparables a las de los fotodetectores convencionales. Por ejemplo, en el grupo del Prof. Edward H. Sargent (Universidad de Toronto, Canadá) han medido detectividades de hasta 1013 jones en la segunda ventana de telecomunicaciones (1.3 μm) en fotodetectores basados en QDs de Pbs, un orden de magnitud mayor que la detectividad lograda en fotodetectores basados en películas delgadas de InGaAs crecidas epitaxialmente. En esta tesis hemos pretendido y conseguido desarrollar fotodetectores basados en QDs de PbS estables en aire y procesados en disolución, con una alta sensibilidad en longitudes de onda del infrarrojo próximo (hasta unos 1600 nm), esto es, útiles para la detección óptica en la tercera ventana de telecomunicaciones. Para conseguir este objetivo principal, primero se ha dedicado el esfuerzo necesario para optimizar la síntesis química de los QDs de PbS con el tamaño adecuado para obtener su borde de absorción en las longitudes de onda señaladas, como base para la producción de películas delgadas con un enfoque ascendente (bottom-up). En segundo lugar, hemos conseguido “nanotintas” estables en aire con estos QDs de PbS, adecuadamente formuladas para su compatibilidad (propiedades reológicas adecuadas) con un método eficiente de deposición en área extensa, que permita la formación de una película delgada de QDs de PbS libre de defectos estructurales (ligados al apilamiento vertical de los QDs, que no son más que nanocristales aproximadamente esféricos de unos 6-7 nm de diámetro). La técnica de deposición elegida ha sido “doctor blading”, donde una cuchilla extiende la nanotinta sobre un substrato dado, en nuestro caso vidrio/ITO (ITO: Indium Tin Oxide) o Si/SiO2, para la fabricación de fotodiodos y fotoconductores, respectivamente. También hemos estudiado la influencia de la química superficial de los QDs de PbS en las propiedades de las películas delgadas producidas con éstos y los dispositivos fabricados con estas capas. De hecho, el paso clave en la formación de películas conductoras con QDs de PbS es el procedimiento de intercambio de ligandos en estado sólido, en el que se reemplazan las moléculas largas (Oleilamina) utilizadas para la síntesis de los QDs de PbS con otras más cortas, con el fin de reducir la distancia entre los QDs, lo que aumentaría la movilidad de los portadores en el sólido de QDs resultante debido a un fuerte acoplamiento electrónico. Específicamente, hemos utilizado el ácido 3-Mercapto-Propiónico (MPA) y el Ioduro de Tetra-butil-amonio (TBAI), lo que ciertamente influye en la superficie de los QDs de PbS y en el rendimiento de los fotodetectores basados en PbS. Encontramos que, en ambos casos, el mecanismo responsable de la fotoconductividad está relacionado con la sensibilización de sólido de QDs por trampas, origen de la alta responsividad observada y la lenta respuesta temporal de los dispositivos fotoconductores. Se ha identificado la importante influencia de los niveles de trampas sobre la dinámica de los portadores y la eficiencia final del dispositivo, además de evidenciar el compromiso entre la velocidad del dispositivo y la alta responsividad de los dispositivos fotoconductores. El intercambio de ligandos en el sólido de QDs con MPA, mientras pasiva eficazmente su superficie, produce un rendimiento superior del dispositivo (mayor foto-sensibilidad y detectividad), lo cual se debe a una menor corriente oscura y menor nivel de ruido en comparación con el caso de los sólidos de QDs tratados con TBAI. Además, el intercambio de ligandos con MPA confiere una excelente estabilidad en aire a los sólidos de QDs, reduciendo la oxidación del PbS, como se deduce de medidas de XPS. Sobre la base de estos hallazgos, finalmente hemos desarrollado un fotodetector estable en aire y altamente sensible (1011 Jones), basado en un fotodiodo de arquitectura Schottky con una eficiencia cuántica interna superior al 30% a 1500 nm y con una respuesta temporal de unos 135 s.Optical sensing and conversion of light into electricity (photovoltaics), on which optoelectronic devices find their more important application field, have been for decades important fields of application for single-crystal semiconductors as photoactive (light absorption and carrier photogeneration) materials. Their success relay on the excellent performances achieved in these devices, which indeed are accompanied by several drawbacks, as high production cost, manufacture complexity and incompatibility with flexible substrates. During the last decade the advent of solution-processed optoelectronic materials, such as colloidal quantum dots (QDs), has opened new prospective for optoelectronic applications. This new approach applied to develop optical detectors lies in the high degree of control offered by nanoscale materials engineering. Moreover, solution-processability of these nanomaterials has enabled their low-cost integration over many commercial substrates, in some cases achieving photodevices with figures of merit comparable to those of conventional photodetectors. For instance, the group of Prof. Edward H. Sargent (Toronto University, Canada) reported detectivities of about 1013 jones in the second telecom window (1.3 μm) for PbS QD-based photodetectors. This is one order of magnitude higher than the detectivity achieved for photodetectors based on epitaxially grown InGaAs thin films. In this thesis we have tried and succeeded in developing photodetectors based on PbS QDs stable in air and processed in solution, with a high sensitivity in near-infrared wavelengths (up to about 1600 nm), that is, useful for optical detection in the third telecommunications window. To achieve this main objective, we have undertaken the necessary efforts to optimize the chemical synthesis of the PbS QDs with the appropriate size to obtain their absorption edge at the indicated wavelengths, these QDs were the basis to produce thin films within a bottom-up approach. Secondly, we have achieved "nanoinks" with these PbS QDs that are stable in air and suitably formulated for their compatibility (adequate rheological properties) with an efficient method of deposition for large areas that allows the formation of a thin film of PbS QDs free of structural defects (associated to the 3D stacking of the QDs, which are approximately spherical nanocrystals of about 6-7 nm in diameter). The chosen large-area deposition technique has been "doctor blading", where a blade extends the ink on a given substrate, in our case glass/ITO (ITO: Indium Tin Oxide) or Si/SiO2, for the fabrication of photodiodes and photoconductors, respectively. We have also studied the influence of the QD surface chemistry on the properties of their produced thin films and fabricated photodevices. In fact, the key step in the formation of conductive PbS QD films is the solid-state ligand exchange procedure by replacing long isolating molecules (Oleylamine) used for the QD synthesis with shorter ones, in order to reduce the interparticle distance, which would increase the carrier mobility in the resulting strongly-coupled QD-solid. Specifically, we have used 3-mercaptopropionic acid (MPA) and tetrabutylammonium iodide (TBAI), which certainly influences the surface of the PbS QDs and the performances of PbS-based photodetectors. We did find that, in both cases, the mechanism responsible of photoconductivity is related to trap sensitization of the QD-solid, which is responsible of the observed high responsivity and low time response of photoconductor devices. The important influence of trap states over the carrier dynamics and the final device performances have been identified, and evidenced the trade-off between device speed and photon detection responsivity of the device. The ligand exchange of the QD-solid film with MPA, while efficiently passivating the PbS QDs, yields a superior device performance (photo-sensitivity and detectivity), which is due to a smaller dark current and lower noise level as compared to the case of PbS QD-solids treated with TBAI. Furthermore, MPA ligand exchange confers excellent long-term air-stability to the QD-solids reducing the oxidation of PbS QDs, as deduced from XPS measurements. Based on these findings, we have finally developed an air-stable highly sensitive (1012 Jones) photodetector based on a simple Schottky photodiode architecture with internal quantum efficiency higher than 30% at 1500 nm and time response of about 135 s