Devices and networks for optical switching

This thesis is concerned with some aspects of the application of optics to switching and computing. Two areas are dealt with: the design of switching networks which use optical interconnects, and the development and application of the t-SEED optical logic device. The work on optical interconnects looks at the multistage interconnection network which has been proposed as a hybrid switch using both electronics and optics. It is shown that the architecture can be mapped from one dimensional to two dimensional format, so that the machine makes full use of the space available to the optics. Other mapping rules are described which allow the network to make optimum use of the optical interconnects, and the endpoint is a hybrid optical-electronic machine which should be able to outperform an all-electronic equivalent. The development of the t-SEED optical logic device is described, which is the integration of a phototransistor with a multiple quantum well optical modulator. It is found to be important to have the modulator underneath rather than on top of the transistor to avoid unwanted thyristor action. In order for the transistor to have a high gain the collector must have a low doping level, the exit window in the substrate must be etched all the way to the emitter layer, and the etch must not damage the emitter-base junction. A real optical gain of 1.6 has been obtained, which is higher than has ever been reached before but is not as high as should be possible. Improvements to the device are suggested. A new model of the Fabry-Perot cavity is introduced which helps considerably in the interpretation of experimental measurements made on the quantum well modulators. Also a method of improving the contrast of the multiple quantum well modulator by grading the well widths is proposed which may find application in long wavelength transmission modulators. Some systems which make use of the t-SEED are considered. It is shown that the t-SEED device has the right characteristics for use as a neuron element in the optical implementation of a neural network. A new image processing network for clutter removal in binary images is introduced which uses the t-SEED, and a brief performance analysis suggests that the network may be superior to an all-electronic machine

Inverted vertical AlGaN deep ultraviolet LEDs grown on p-SiC substrates by molecular beam epitaxy

Deep ultraviolet light emitting diodes (UV LEDs) are an important emerging technology for a number of applications such as water/air/surface disinfection, communications, and epoxy curing. However, as of yet, deep UV LEDs grown on sapphire substrates are neither efficient enough nor powerful enough to fully serve these and other potential applications. The majority of UV LEDs reported so far in the literature are grown on sapphire substrates and their design consists of AlGaN quantum wells (QWs) embedded in an AlGaN p-i-n junction with the n-type layer on the sapphire. These devices suffer from a high concentration of threading defects originating from the large lattice mismatch between the sapphire substrate and AlGaN alloys. Other issues include the poor doping efficiency of the n- and particularly the p-AlGaN alloys, the extraction of light through the sapphire substrate, and the heat dissipation through the thermally insulating sapphire substrate. These problems have historically limited the internal quantum efficiency (IQE), injection efficiency (IE), and light extraction efficiency (EE) of devices. As a means of addressing these efficiency and power challenges, I have contributed to the development of a novel inverted vertical deep UV LED design based on AlGaN grown on p-SiC substrates. Starting with a p-SiC substrate that serves as the p-type side of the p-i-n junction largely eliminates the necessity for the notoriously difficult p-type doping of AlGaN alloys, and allows for efficient heat dissipation through the highly thermally conductive SiC substrate. UV light absorption in the SiC substrate can be addressed by first growing p-type doped distributed Bragg reflectors (DBRs) on top of the substrate prior to the deposition of the active region of the device. A number of n-AlGaN films, AlGaN/AlGaN multiple quantum wells, and p-type doped AlGaN DBRs were grown by molecular beam epitaxy (MBE). These were characterized in situ by reflected high energy electron diffraction (RHEED) and ex situ by x-ray diffraction, scanning electron microscopy, atomic force microscopy, photoluminescence, and reflectivity. Using the primary elements of the proposed design, this research culminated in the MBE growth, fabrication, and characterization of prototype deep UV LED devices emitting below 300 nm

Optoelectronics – Devices and Applications

Optoelectronics - Devices and Applications is the second part of an edited anthology on the multifaced areas of optoelectronics by a selected group of authors including promising novices to experts in the field. Photonics and optoelectronics are making an impact multiple times as the semiconductor revolution made on the quality of our life. In telecommunication, entertainment devices, computational techniques, clean energy harvesting, medical instrumentation, materials and device characterization and scores of other areas of R&D the science of optics and electronics get coupled by fine technology advances to make incredibly large strides. The technology of light has advanced to a stage where disciplines sans boundaries are finding it indispensable. New design concepts are fast emerging and being tested and applications developed in an unimaginable pace and speed. The wide spectrum of topics related to optoelectronics and photonics presented here is sure to make this collection of essays extremely useful to students and other stake holders in the field such as researchers and device designers

Deviation of Time-Resolved Luminescence Dynamics in MWIR Semiconductor Materials from Carrier Recombination Theory Predictions

Time resolved luminescence spectroscopy was used to characterize luminescence decay curves for a bulk InAs sample and an InAsSb type-I quantum-well sample over the first 3ns following excitation. The luminescence decay curves were then converted to carrier densities and used to find recombination coefficients that provided the least-squared-error solution of the rate equation describing carrier recombination. Recombination coefficients describing Shockley Read-Hall (ASRH) radiative (Brad) and Auger (CAug) recombination were determined at two different temperatures and four excitation powers, then analyzed for consistency and physical significance. For all of the resulting least squares fits a minimum of one recombination coefficient was negative. While this could be explained in terms of unconfined carriers in the quantum structure the lack of a trend in the parameters with excitation power indicates that this has not the sole contributing factor. No explanation for this behavior could be formulated for the bulk InAs sample. As an alternative approach luminescence decay curves were directly analyzed to evaluate the possibility that the anomalous behavior was an artifact of the initial luminescence-to- carrier density mapping. Again the least squares fit resulted in negative coefficients. Furthermore when the parameters were constrained to be positive the best fit was significantly worse than the unconstrained case. This indicated that negative parameters were not simply an artifact of noise in the data

Design and Fabrication of Micro-Electro-Mechanical Structures for Tunable Micro-Optical Devices

Tunable micro-optical devices are expected to be vital for future military optical communication systems. In this research I seek to optimize the design of a microelectromechanical (MEM) structure integrated with a III-V semiconductor micro-optical device. The resonant frequency of an integrated optical device, consisting of a Fabry-Perot etalon or vertical cavity surface emitting laser (VCSEL), may be tuned by applying an actuation voltage to the MEM Flexure, thereby altering the device\u27s optical cavity length. From my analysis I demonstrate tunable devices compatible with conventional silicon 5V integrated circuit technology. My design for a Fabry-Perot etalon has a theoretical tuning range of 200 nm, and my VCSEL design has a tuning range of 44nm, both achieved with actuation voltages as low as 4V. Utilizing my theoretical device designs I planned a new microelectronics fabrication process to realize a set of prototype MEM-tunable devices with a peak central emission wavelength at 980nm. I designed a mask set consisting of 8 mask levels and 252 distinct device designs, all within a die size of one square centimeter. My unique fabrication process utilizes a gold MEM flexure with a Si3N4/SiO2 dielectric distributed Bragg reflector (DBR) mirror, grown on an all-semiconductor VCSEL or Fabry-Perot substrate. I successfully fabricated a complete set of MEM-tunable test structures using the cleanroom laboratory facilities at the Air Force Institute of Technology (AFIT) and the Air Force Research Laboratory (AFRL). The initial devices display minimum electrostatic actuation voltages as low as 1.8 V, which is comparable to existing MEM tunable VCSEL designs. In order to enhance device performance, I developed improvements to my laboratory process for incorporation in future fabrication runs. These results form the fundamental basis for advanced development of manufacturable MEM-tunable optical emitting and detecting device arrays

Optical surfaces for mid-infrared sensing

The mid-infrared (mid-IR) spectral region, with wavelengths between 3 and 15 µm, is known for a wide range of applications ranging from spectroscopic sensing to thermal imaging. However, despite the strong technological interest, optoelectronic devices in the mid-IR are expensive and often inferior in performance compared to their visible and near-IR counterparts. In this thesis, we combine ultrathin materials, e.g. graphene, and novel substrates to develop optical surfaces for applications in the mid-IR.First, we demonstrate a novel uncooled photodetector, combining graphene with a ferroelectric (pyroelectric) substrate. More specifically, we develop a graphene on z-cut lithium niobate (LiNbO3) pyro-resistive platform that supports dynamic tunablity of the responsivity. We also develop a model to identify the key parameters that influence the performance of such detectors and can therefore provide guidelines to improve their performance. Second, we introduce ultra-thin yttria-stabilized zirconia (YSZ), a ceramic material, as a novel platform for IR nano-optics. In particular, we combine YSZ substrates with metallic nanostructures and graphene to demonstrate plasmonic, polarizing and transparent heating devices, which enable high temperature processing and can withstand harsh environments thanks to the high thermal and chemical stabilities of YSZ. Additionally, the mechanical flexibility of YSZ substrates also makes them ideally suited for manufacturing foldable or bendable devices and for low cost large-scale roll-to-roll fabrication processes. Finally, we investigate for the first time electrostatically tunable graphene nano-hole array surfaces by performing a detailed experimental study of structures with periods as low as 100 nm. We obtain a clear plasmonic response from these surfaces in the range 1300-1600 cm-1. We also demonstrated for the first time that these tunable nanostructures can be fabricated by scalable nano-imprint technique. Such large area plasmonic nanostructures are suitable for industrial applications, for example, surface-enhanced infrared absorption (SEIRA) sensing. This is because they combine an easy design, extreme field confinement and the possibility to excite multiple plasmon modes for multiband sensing, a feature not readily available in nanoribbons or other localized resonant geometries. The results contained in this thesis are particularly relevant with regard to extending the use of materials, such as graphene combined with specific substrates (LiNbO3 or zirconia), to mid-IR photodetection, enhanced absorption and molecular sensing.La región espectral del infrarrojo medio (mid-IR), de longitudes de onda entre los 3 y los 15µm, se conoce por su vasto número de aplicaciones: desde la detecciónespectroscópica hasta la imagen térmica. No obstante, a pesar de su gran interéstecnológico, los dispositivos optoelectrónicos en el mid-IR son caros y, a menudo,con rendimientos inferiores al compararlos con sus homólogos en la región visibley en el infrarrojo cercano. En esta tesis, combinamos materiales ultrafinos(e.g. grafeno) con nuevos substratos para desarrollar superficies ópticas conaplicaciones en el mid-IR.Primero, mostramos los resultados de un fotodetector innovador, que nonecesita ser enfriado, fabricado combinando grafeno con un substrato ferroeléc-trico (piroeléctrico). Más específicamente, desarrollamos un artefacto de grafenodispuesto sobre niobato de litio (LiNbO3) cortado en la dirección z, que admiteuna modulación dinámica de su capacidad de respuesta. También desarrollamosun modelo matemático con el propósito de identificar los parámetros claves queinfluyen en el rendimiento de estos fotodetectores y, en consecuencia, propor-cionar una serie de pautas para mejorarlo. En segundo lugar, introducimos la circonita estabilizada con óxido de itrioultrafina (YSZ) como material cerámico vanguardista en el campo de la nanoóp-tica en el IR. En particular, combinamos substratos de YSZ con nanoestructurasmetálicas y grafeno para demostrar la idoneidad de dispositivos plasmónicos,transparentes y polarizadores, que posibilitan el procesamiento a alta temper-atura y que pueden soportar condiciones ambientales más duras gracias a laexcelente estabilidad térmica y química de la YSZ. Además, la flexibilidad delos substratos de YSZ hace de éstas, unas estructuras ideales para la manufactura de dispositivos flexibles y plegables, cuyo proceso rollo-a-rollo de fabricacióna gran escala es de bajo coste. Finalmente, investigamos por vez primera las superficies de grafeno modu-ladas electrostáticamente con patrones de nano-orificios, cuyos periodos llegana distancias tan pequeñas como los 100 nm, por medio de un exhaustivo estudioexperimental. A través del mismo, obtenemos una respuesta plasmónica claraen el rango de los 1300-1600cm-1. También demostramos por primera vez, queestas nanoestrucutras modulables pueden ser fabricadas mediante técnicas es-calables de nanoimpresión. Las grandes dimensiones de dichas nanoestructurasplasmónicas, las hacen plenamente apropiadas para aplicaciones industrialescomo, por ejemplo, la detección por absorción infrarroja amplificada de super-ficie (SEIRA, por sus siglas en inglés). Esto ocurre debido a que combinan undiseño simple, con un confinamiento extremo del campo y con la posibilidad deexcitar diferentes modos plasmónicos, lo que es de gran utilidad para la detec-ción multi-banda, una característica difícil de conseguir con cintas de grafeno uotras geometrías localizadas resonantes. Los resultados integrados en esta tesisson particularmente relevantes con respecto a la extensión de la utilización demateriales como el grafeno en combinación con substratos específicos (LiNbO3o circonita) para la fotodetección en el mir-IR, la absorción amplificada y ladetección molecular.Postprint (published version

Graphene Integrated Metamaterial Devices for Terahertz Modulation

Terahertz (THz) research has experienced impressive progress in recent decades, with unique applications emerging in fields such as spectroscopy, communications, and imaging, all of which require fast and accurate control of the THz radiation properties. To unlock the full potential of THz radiation, it is essential to develop a catalogue of high speed, electrically controllable modular THz devices, which can be implemented with standardised sources to build versatile THz systems. Due to THz frequencies lying outside of the typical operation range for the mature microwave and photonic technologies, alternative approaches are required to solve the unique engineering problems associated with operating in this frequency regime. This thesis will look to design and develop novel device architectures using metamaterial arrays to strongly couple with THz radiation, whilst implementing electrically tunable graphene to modify the strength and nature of this interaction, leading to active control of the amplitude, phase, polarisation and frequency of THz radiation. Chapter 1 discusses two THz sources: THz time-domain spectroscopy (THz-TDS) and THz quantum cascade lasers (THz-QCLs). A range of THz modulator architectures will then be discussed, focusing on the methods which involve converting passive metamaterial arrays into actively tunable devices, including the implementation of microelectromechanical systems (MEMS), photoactive semiconductors, and electrostatically tunable graphene. Chapter 2 outlines the basic device design principles for the graphene integrated metamaterial devices shown in this thesis. The steps to build a basic split ring resonator (SRR) and graphene amplitude modulator device are discussed, starting with the design process using finite element electromagnetic simulation, before outlining the fabrication steps required to build the device, and finally performing the experimental procedure to test the device performance in a THz-TDS system. The SRR/graphene device discussed in this chapter demonstrates amplitude modulation depths in the region of 12 %, achieved by electrostatically tuning the graphene conductivity using a voltage range of 30 V. Chapter 3 investigates more sophisticated graphene integrated metamaterial devices which involve lithographically selecting targeted areas of the metamaterial structure to be actively tuned by graphene. More interesting modulation effects, such as resonant frequency tuning, are achieved by integrating a coupled resonator metamaterial array with targeted graphene damping. A continuous tuning of the resonant frequency over a 60 GHz range, and binary tuning of over 200 GHz are achieved. Due to the highly dispersive nature of the coupled resonator array, dramatic phase and group delay modulation effects are also demonstrated. Chapter 4 builds on the work from chapter 3, converting the coupled resonator and graphene devices into polarisation modulators by adding an intrinsic chirality into the metamaterial design. Two different devices are designed and fabricated, both achieving electrical control over the polarisation angle and ellipticity of the transmitted radiation. Polarisation tuning of up to 30 degrees is experimentally confirmed, with linear radiation successfully converted into perfectly circular radiation, achieving an ellipticity tuning range from 0.6 to 1.0. Chapter 5 discusses the implementation of the active devices described in the previous chapters with quantum cascade lasers, for the conversion of a standard THz source into a highly versatile amplitude, polarisation and frequency controllable modular THz system. MHz modulation speeds of QCLs are achieved by directing a QCL output through the polarisation devices, with the polarisation angle actively tuned by up to 9 degrees. Dramatic modulation effects are achieved by externally coupling radiation back into a QCL using the devices as electrically tunable mirrors in an external cavity configuration. 100 % amplitude modulation of the QCL is achieved using this method, and the frequency of THz output is also successfully manipulated, with 20 GHz binary tuning of the laser output achieved. Chapter 6 discusses future methods which could be used to enhance the modulation depths of the devices described in this thesis. A modified reflection modulation scheme is proposed and theoretically described which could greatly enhance the tuning range of the modulators. Preliminary TDS experiments are performed showing near 100 % amplitude modulation depths by employing this modulation scheme. Further to this, a continuous π/2 phase tuning range is achieved, corresponding to a 10 times improvement compared to the standard transmission and reflection modulation schemes. A modified QCL feedback scheme is also described which could utilize this enhanced phase modulation to achieve continuous tuning of the QCL output over 10s of GHz. A similar scheme is simulated to produce greatly enhanced polarization modulation depths with nearly 90 degrees polarization angle tuning, and near linear to perfectly circular polarisation modulation predicted. A potential modular TDS set-up is also proposed which involves implementing the polarisation modulators into the standard set-up, for fast material birefringence characterisation

Degradation mechanisms of devices for optoelectronics and power electronics based on Gallium Nitride heterostructures

Gallium Nitride is rapidly emerging as a promising material for electronic devices in various fields. Since it is a direct bandgap semiconductor it can be used for highly efficient light emitting devices (Light Emitting Diodes and Laser Diodes) and the possibility of growing alloys containing Aluminum and Indium allow for the selection of the peak wavelength along the whole UV-green part of the radiation spectrum. Moreover, the high electron mobility, the ability of withstand high electric fields and the good thermal dissipation make GaN-based diodes and transistors devices with a good potential for high frequency and power applications. Before final products containing Gallium Nitride devices can permeate the international market, it is required to guarantee that they are reliable enough to have long lifetimes to appeal potential customers, and that their performance/cost relationship is superior compared to other competitors, at least in some specific fields of application. Aim of this thesis is to investigate the strong points of Gallium Nitrides by means of characterization and reliability tests on various different structures (LEDs, laser diodes, blocking diodes, HEMTs, GITs, MISs), in order to analyze the behavior of the material from different points of view. Within this work is reported a detailed study of the gradual degradation of InGaN-based laser diodes and Light-Emitting Diodes submitted to electro-thermal stress. The purpose is to compare the behavior of the two devices by means of electro-optical measurements, electroluminescence characterization, near field emission measurements and Deep-Level Transient Spectroscopy (DLTS) investigation in order to give a deeper understanding of the mechanisms involved in LD degradation. Particular attention is given to the role of injection efficiency decrease and non-radiative recombination. The comparison of the degradation kinetics and an analysis of the degradation modes of the two device structures allowed a complete study of the physical mechanisms responsible for the degradation. It was found that the degradation of the devices can be ascribed to an increase of the defect density, which has a strong impact on non radiative recombination kinetics. The activation energy of the detected deep level is 0.35 - 0.45 eV. As an effect of combined electrical and thermal stress tests on commercially-available InGaN-based blue laser diodes, it has been found that sometimes there is an initial decrease of the threshold current, which is ascribed to the increase of the activation of p-type dopant, promoted by the temperature and the flow of minority carriers. In order to investigate the effects of the creation of defects, two different commercial blue InGaN-based LEDs were submitted to 3 MeV proton irradiation at various fluencies (10^11, 10^12 and 10^13 p/cm2). The degradation process was characterized by combined current-voltage (I - V), optical power-current (L - I) and capacitance-voltage (C - V) measurements, in order to investigate the changes induced by the irradiation and the recovery after annealing time at high temperature (150 °C). The experimental data suggest the creation of non-radiative recombination centers near or into the active region of the LEDs, due to atomic displacement. This hypothesis is confirmed by the results of the recovery tests: the increase of the optical power and its correlation with the recovery of the forward current is consistent with the annealing of those defects. Part of the activity on high electron mobility transistors was devoted to the realization of measurement setups in order to carry out novel characterization techniques. Were analyzed the advantages and limitations of the current-transient method used for the study of the deep levels in GaN-based high electron mobility transistors (HEMTs), by evaluating how the procedures adopted for measurement and data analysis can influence the results of the investigation. The choice of the measurement parameters (such as the voltage levels used to induce the trapping phenomena and monitor the current transients and the duration of the filling pulses) and of the analysis procedure (the method used for the extrapolation of the time constants of the processes) can influence the results of the drain current transient investigation and can provide information on the location of the trap levels responsible for current collapse. Moreover, was collected a database of defects described in more than 60 papers on GaN and its compounds, which can be used to extract information on the nature and origin of the traps in AlGaN/GaN HEMTs. Using this newly developed technique and other more common tests, several reliability and lifetime test were carried out on various structures, in order to gain a better understanding of their problematic aspects and possible improvements. One potential variation is the composition of the gate stack. Degradation tests were performed at Vgs = -5 V and increasing Vds levels on GaN HEMTs with different gate materials: Ni/Au/Ni, ITO and Ni/ITO. At each step of the stress experiment, the electrical and optical characteristics of the transistors were measured in order to analyze the degradation process. It was found that stress induces a permanent degradation of the gate diode, consisting in an increase in the leakage current. This change is due to the generation of parasitic conductive paths, as suggested by electroluminescence (EL) mapping, and devices based on ITO showed higher reliability. These data strongly support the hypothesis that the robustness is influenced by processing parameters and/or by the gate material, since all analyzed devices come from the same epitaxial wafer. Other than varying the gate material, it is possible to add a p-type layer under the gate in order to achieve normally-off operation. This change produces a benefit in terms of performances, but can give birth to unusual trapping phenomena. It was carried out an extensive analysis of the time and field-dependent trapping processes that occur in GaN-based gate injection transistors exposed to high drain voltage levels. Results indicate that, even if the devices do not suffer from current collapse, continuous exposure to high drain voltages can induce a remarkable increase in the on-resistance (Ron). The increase in Ron can be recovered by leaving the device in rest conditions. Temperature-dependent analysis indicates that the activation energy of the detrapping process is equal to 0.47 eV. By time-resolved electroluminescence characterization, it is shown that this effect is related to the capture of electrons in the gate - drain access region. This is further confirmed by the fact that charge emission can be significantly accelerated through the injection of holes from the gate. A first-order model was developed to explain the time dependence of the trapping process. Using other deep levels characterization techniques, such as drain current transients, gate frequency sweeps and backgating, several other trap states were identified in these devices. Their activation energies are 0.13, 0.14, 0.25, 0.47 and 0.51 eV. During the accelerated lifetime tests of these devices, it was found a variation of the relative amplitude of the transconductance peaks, well correlated with the increase of the electroluminescence. This effect can be explained by the activation of the p-type dopant, a phenomenon which was detected also in laser diodes. It is possible to develop diodes able to withstand very high reverse voltages using a similar structure, deprived of the gate region and with an additional Schottky diode (Natural superjunction). In this case, the activation energies of the detected deep levels were 0.35, 0.36, 0.44 and 0.47 eV. These values are very similar to the ones found in GITs, and this fact, along with the presence of the p-dopant activation in very different devices, confirms that it is useful to study different structures based on the same material in order to gain more knowledge on its performances, possibilities and reliability aspects

Optical surfaces for mid-infrared sensing

The mid-infrared (mid-IR) spectral region, with wavelengths between 3 and 15 µm, is known for a wide range of applications ranging from spectroscopic sensing to thermal imaging. However, despite the strong technological interest, optoelectronic devices in the mid-IR are expensive and often inferior in performance compared to their visible and near-IR counterparts. In this thesis, we combine ultrathin materials, e.g. graphene, and novel substrates to develop optical surfaces for applications in the mid-IR.First, we demonstrate a novel uncooled photodetector, combining graphene with a ferroelectric (pyroelectric) substrate. More specifically, we develop a graphene on z-cut lithium niobate (LiNbO3) pyro-resistive platform that supports dynamic tunablity of the responsivity. We also develop a model to identify the key parameters that influence the performance of such detectors and can therefore provide guidelines to improve their performance. Second, we introduce ultra-thin yttria-stabilized zirconia (YSZ), a ceramic material, as a novel platform for IR nano-optics. In particular, we combine YSZ substrates with metallic nanostructures and graphene to demonstrate plasmonic, polarizing and transparent heating devices, which enable high temperature processing and can withstand harsh environments thanks to the high thermal and chemical stabilities of YSZ. Additionally, the mechanical flexibility of YSZ substrates also makes them ideally suited for manufacturing foldable or bendable devices and for low cost large-scale roll-to-roll fabrication processes. Finally, we investigate for the first time electrostatically tunable graphene nano-hole array surfaces by performing a detailed experimental study of structures with periods as low as 100 nm. We obtain a clear plasmonic response from these surfaces in the range 1300-1600 cm-1. We also demonstrated for the first time that these tunable nanostructures can be fabricated by scalable nano-imprint technique. Such large area plasmonic nanostructures are suitable for industrial applications, for example, surface-enhanced infrared absorption (SEIRA) sensing. This is because they combine an easy design, extreme field confinement and the possibility to excite multiple plasmon modes for multiband sensing, a feature not readily available in nanoribbons or other localized resonant geometries. The results contained in this thesis are particularly relevant with regard to extending the use of materials, such as graphene combined with specific substrates (LiNbO3 or zirconia), to mid-IR photodetection, enhanced absorption and molecular sensing.La región espectral del infrarrojo medio (mid-IR), de longitudes de onda entre los 3 y los 15µm, se conoce por su vasto número de aplicaciones: desde la detecciónespectroscópica hasta la imagen térmica. No obstante, a pesar de su gran interéstecnológico, los dispositivos optoelectrónicos en el mid-IR son caros y, a menudo,con rendimientos inferiores al compararlos con sus homólogos en la región visibley en el infrarrojo cercano. En esta tesis, combinamos materiales ultrafinos(e.g. grafeno) con nuevos substratos para desarrollar superficies ópticas conaplicaciones en el mid-IR.Primero, mostramos los resultados de un fotodetector innovador, que nonecesita ser enfriado, fabricado combinando grafeno con un substrato ferroeléc-trico (piroeléctrico). Más específicamente, desarrollamos un artefacto de grafenodispuesto sobre niobato de litio (LiNbO3) cortado en la dirección z, que admiteuna modulación dinámica de su capacidad de respuesta. También desarrollamosun modelo matemático con el propósito de identificar los parámetros claves queinfluyen en el rendimiento de estos fotodetectores y, en consecuencia, propor-cionar una serie de pautas para mejorarlo. En segundo lugar, introducimos la circonita estabilizada con óxido de itrioultrafina (YSZ) como material cerámico vanguardista en el campo de la nanoóp-tica en el IR. En particular, combinamos substratos de YSZ con nanoestructurasmetálicas y grafeno para demostrar la idoneidad de dispositivos plasmónicos,transparentes y polarizadores, que posibilitan el procesamiento a alta temper-atura y que pueden soportar condiciones ambientales más duras gracias a laexcelente estabilidad térmica y química de la YSZ. Además, la flexibilidad delos substratos de YSZ hace de éstas, unas estructuras ideales para la manufactura de dispositivos flexibles y plegables, cuyo proceso rollo-a-rollo de fabricacióna gran escala es de bajo coste. Finalmente, investigamos por vez primera las superficies de grafeno modu-ladas electrostáticamente con patrones de nano-orificios, cuyos periodos llegana distancias tan pequeñas como los 100 nm, por medio de un exhaustivo estudioexperimental. A través del mismo, obtenemos una respuesta plasmónica claraen el rango de los 1300-1600cm-1. También demostramos por primera vez, queestas nanoestrucutras modulables pueden ser fabricadas mediante técnicas es-calables de nanoimpresión. Las grandes dimensiones de dichas nanoestructurasplasmónicas, las hacen plenamente apropiadas para aplicaciones industrialescomo, por ejemplo, la detección por absorción infrarroja amplificada de super-ficie (SEIRA, por sus siglas en inglés). Esto ocurre debido a que combinan undiseño simple, con un confinamiento extremo del campo y con la posibilidad deexcitar diferentes modos plasmónicos, lo que es de gran utilidad para la detec-ción multi-banda, una característica difícil de conseguir con cintas de grafeno uotras geometrías localizadas resonantes. Los resultados integrados en esta tesisson particularmente relevantes con respecto a la extensión de la utilización demateriales como el grafeno en combinación con substratos específicos (LiNbO3o circonita) para la fotodetección en el mir-IR, la absorción amplificada y ladetección molecular