This thesis is focused on a study of CdTe and CdZnTe semiconductor detectors working under high flux of radiation. We studied experimentally an influence of high flux of X-rays and optical radiation on polarization of the detector. The polarization phenomenon decreases the efficiency of the detector due to a screening of an applied electric field by a space charge accumulated at deep levels due to a trapping of photogenerated carriers. In order to measure the electric field profiles in the detectors we employed a method based on cross polarizers technique and Pockels effect. The main objective of this work was to study the possibilities of an optical de-polarization of CdTe and CdZnTe detectors for different photon energies of additional light, its dynamics and physical origin. We have found that detectors can be de-polarized by above bandgap light. Moreover, CdZnTe detector can be depolarized by near infrared light and in a pulse mode. The de- polarization is associated with a compensation of the space charge at deep traps.

L’objet de ces travaux de thèse a été de réaliser un système compact et non-invasifde mesure vectorielle de champs électriques. Ce système est dédié aux mesures en espacelibre (diagramme de rayonnement d’antennes) ainsi qu’aux mesures en champ proche(diagnostic de circuits électriques par exemple). Pour ce faire, nous avons proposé unsystème de mesure utilisant d’une part des sondes électro-optique fibrées, dont la partietransductrice est composée d’un guide d’onde en LiNbO3, intégrée dans une cavité Fabry-Pérot. Le cristal non-linéaire induit une modulation de phase d’un faisceau laser de sonde,dépendante du champ électrique à mesurer. La cavité, quant à elle, convertit le signal enmodulation d’amplitude et permet de réduire la taille du capteur grâce à l’augmentationde la longueur effective d’interaction entre l’onde optique et le champ électrique à mesurer.D’autre part l’étude d’un filtrage optique de très grand facteur de qualité associé à unepost-amplification est proposée, dans le but d’accroître d’au moins un ordre de grandeurla sensibilité de mesure. / The aim of this work is to design and realize a compact and non-invasive system dedicatedto vectorial characterization of electric field. The field to be measured can be eitherradiated (for antenna radiation pattern) or guided (for on chip measurement). We herepropose a measurement system including pigtailed electro-optic probe. The transducingdevice is based on a Fabry-Pérot (FP) cavity integrating LiNbO3 waveguide. The nonlinearcrystal induces a phase modulation of a laser probe beam depending on the theelectric field to be characterized. The FP cavity converts the signal into a linear amplitudemodulation and leads to a millimeter sized sensor thanks to the enhancement ofthe effective interactive length between the optical wave and the electric field. The sensorexhibits a sensitivity greater than 0.5 V.m−1.Hz−1/2, a spatial resolution as accurate as100 μm and a frequency bandwidth covering [10 Hz-10 GHz]. Moreover, we here suggesta high quality factor post-filtering of the optical carrier in order to increase the sensitivityof one order of magnitude.

En premier lieu, des couches minces épitaxiales ont été obtenues sur des substrats de silicium grâce à l’utilisation de l’épitaxie par jets moléculaire et de couches tampons de titanate de strontium SrTiO3. Une technique de croissance par co-déposition a été développée de manière à obtenir un rapport Ba:Ti proche de la stoechiométrie, et ce afin d’éviter la formation de défauts cristallins dans la couche de BaTiO3. Le matériau déposé cristallise dans une structure de symétrie quadratique, ce qui est unpré-requis pour l’obtention de propriétés électro-optiques. De plus, selon les conditions de croissance, l’axe c de la maille élémentaire quadratique a pu être ajusté de manière à être aligné parallèlement ou perpendiculairement à la surface du substrat. L’utilisation d’une mince couche tampon de nucléation a également permis de croitre des films mincesBaTiO3 épitaxiées par pulvérisation, technique largement répandue en milieu industriel.Un coefficient de Pockels élevé a par la suite été obtenu sur de tellescouches épitaxiées. La valeur mesurée de 148pmV est clairement supérieure aux valeurs admises dans la littérature pour d’autres matériaux nonlinéairestels que le niobate de lithium, pour lequel un coefficient de31pmV est rapporté. La méthode de caractérisation électro-optique développée à cette occasion révèle également le caractère ferroélectrique des couches de BaTiO3, observé pour la première fois dans de tels matériaux épitaxiés sur silicium.Finalement, ces couches minces électro-optiquement actives ont été intégrées dans des dispositifs photoniques sur silicium. Dans cette optique,une structure de guide d’onde à fente a été utilisée en insérant 50nm deBaTiO3 entre deux couches de silicium. Dans ce type de structure, le confine mentoptique est 5 fois supérieur à celui obtenu pour des guides d’onde en silicium avec une gaine à base de BaTiO3. Des guides d’ondes rectilignesont tout d’abord été fabriqués, pour lesquels des pertes optiques del’ordre de 50−100 dB/cm ont été mesurées. Par la suite, des composants passifs fonctionnels ont été fabriqués, tels que des interféromètres typeMach-Zehnder, des résonateurs circulaires et des coupleurs. Finalement,la fonctionnalité de composants actifs a été démontrée pour la première fois, en se basant notamment sur des résonateurs ayant un facteur de qualité Q d’environ 5000, et pour lequel la résonance varie en fonction du champ électrique transverse. L’origine physique de cette variation n’a cependant pas pu être expliquée sur la seule base de l’effet Pockels. Cette thèse démontre que l’utilisation de nouveaux matériaux électro optiquement actifs au coeur de dispositifs photoniques sur silicium créede nouvelles opportunités pour la conception et l’ingénierie de circuitsphotoniques. L’intégration d’oxydes tels que barium titanate permet d’envisager de nouveaux concepts de dispositifs pour ajuster, moduler ou commuter la lumière au sein de circuits photoniques denses. De nouveaux défis et perspectives s’ouvrent également aux scientifiques pour modifier artificiellement les propriétés électro-optiques de ces matériaux, que ce soit par contrainte, dopage ou par l’ingénierie de multicouches. De telles avancées pourront sans aucun doute fortement améliorer les performances des dispositifs. / A novel concept of utilizing electro-optical active oxides in silicon photonic devices is developed and realized in the frame of this thesis. The integration of such oxides extends the silicon photonics platform by non-linear materials, which can be used for ultra-fast switching or low-power tuning applications. Barium titanate is used as active material as it shows one of the strongest Pockels coefficients among all oxides. Three major goals are achieved throughout this work: First, thin films of BaTiO3 are epitaxially grown on silicon substrates via molecular beam epitaxy (MBE) using thin SrTiO3 buffer layers. A shuttered co-deposition growth technique is developed in order to minimize the formation of defects in the BaTiO3 films by achieving a 1:1 stoichiometry between barium and titanium. The layers show a tetragonal symmetry and are therefore well-suited for electro-optical applications. The orientation of the long c -axis of the BaTiO3 crystal can be tuned to point perpendicular or parallel to the film surface, depending on the growth conditions. In addition, thin MBE-grown seed layers are combined with rf-sputter deposition. With this hybrid growth approach, rather thick ( > 100 nm), epitaxial BaTiO3 layers on silicon substrates are obtained with a commercially available, wide spread deposition technique. As a second goal, a strong Pockels coefficient of reff = 148 pm/V is determined in the epitaxial BaTiO3 films. This first experimental result on the electro-optical activity of BaTiO3 layers on silicon shows a clear enhancement compared to alternative non-linear materials such as lithium niobate with reff = 31 pm/V. By means of the electro-optical characterization method, also the presence of ferroelectricity in the films is demonstrated. Third, the electro-optical active BaTiO3 layers are embedded into silicon photonic devices. For this purpose, a horizontal slot-waveguide structure with a ~50 nm-thick BaTiO3 film sandwiched between two silicon layers is designed. With this design, the optical confinement in the active BaTiO3 layer is enhanced by a factor of 5 compared to Si-waveguide structures with a standard cross section and BaTiO3 as cladding. Straight BaTiO3 slot-waveguides with propagation losses of 50 − 100 dB/cm as well as functional passive devices such as Mach-Zehnder-interferometers, couplers, and ring resonators are experimentally realized. Additionally, first active ring resonators with Q-factors of Q~5000 are fabricated. The physical origin of the observed resonance shift as a function of the applied bias voltage, however, can not be conclusively clarified in the present work. The combination of high-quality, functional BaTiO3 layers with silicon photonic devices as demonstrated in this thesis offers new opportunities by extending the design palette for engineering photonic circuits with the class of electro-opticalactive materials. The integration of oxides such as BaTiO3 enables novel device concepts for tuning, switching, and modulating light in extremely dense photonic circuits. The integration also opens exciting challenges for material scientists to tailor the electro-optical properties of those oxides by strain engineering or fabrication of superlattice structures, which could ultimately lead to another boost of their electro-optical properties.

Title: Point defects in materials for detection of X-ray and gamma radiation Author: Martin Rejhon Department: Institute of Physics of Charles University Supervisor: prof. Ing. Jan Franc, DrSc., Institute of Physics of Charles Uni- versity Abstract: Cadmium telluride and its compounds are suitable materials for pro- duction of X-ray and gamma-ray detectors working at room temperature. How- ever, the detector quality is affected by material imperfections, such as crystal defects and impurities. It results into forming of deep levels which act as re- combination and trapping centers. Then, the accumulated space charge at these deep levels influences electric and spectroscopic properties of the detector. In the end it may result in the polarization effect, when the electric field is localized in vicinity of one contact and detection properties are decreased. This thesis reports a complex study of a detector band structure by various meth- ods with focus on differences between CdTe, CdZnTe, CdTeSe and CdZnTeSe. The electro-optic Pockels effect is used to investigate the influence of the illumi- nation in range 900 − 1800 nm on the inner electric field. The temperature and time evolutions of the electric field after application of bias or switching of the additional light at 940 nm were measured to determine deep levels...

Title: Point defects in materials for detection of X-ray and gamma radiation Author: Martin Rejhon Department: Institute of Physics of Charles University Supervisor: prof. Ing. Jan Franc, DrSc., Institute of Physics of Charles Uni- versity Abstract: Cadmium telluride and its compounds are suitable materials for pro- duction of X-ray and gamma-ray detectors working at room temperature. How- ever, the detector quality is affected by material imperfections, such as crystal defects and impurities. It results into forming of deep levels which act as re- combination and trapping centers. Then, the accumulated space charge at these deep levels influences electric and spectroscopic properties of the detector. In the end it may result in the polarization effect, when the electric field is localized in vicinity of one contact and detection properties are decreased. This thesis reports a complex study of a detector band structure by various meth- ods with focus on differences between CdTe, CdZnTe, CdTeSe and CdZnTeSe. The electro-optic Pockels effect is used to investigate the influence of the illumi- nation in range 900 − 1800 nm on the inner electric field. The temperature and time evolutions of the electric field after application of bias or switching of the additional light at 940 nm were measured to determine deep levels...

[ES] En la última década, la plataforma de silicio ha emergido como la plataforma por excelencia para desarrollar circuitos fotónicos integrados debido a su versatilidad, la posibilidad de miniaturización y de una producción de bajo coste y a gran escala compatible con los sistemas CMOS ("complementary metal-oxide semiconductor"). La conversión de señales eléctricas a alta velocidad en señales ópticas es una función crítica hoy en día tanto para el procesamiento de datos como en el ámbito de las telecomunicaciones. La forma más eficaz de implementar actualementeuna ,modulación electro-óptica ultra-rápida se basa en el efecto Pockels que, de hecho,se encuentra en el corazón de los moduladores comerciales basados en niobato de litio y polímeros. Sin embargo, la implementación de esta funcionalidad se ve impedida en la plataforma de silicio debido a la simetría de inversión de la red cristalina del silicio. En este contexto, el silicio deformado surgió hace más de un decenio como una solución revolucionaria para romper esa centrosimetría y, de ese modo, hacer emerger no-linealidades de segundo orden en el propio silicio. Sin embargo, y a pesar de los alentadores resultados iniciales, estudios posteriores cuestionaron el origen de las respuestas obtenidas, achacando dichos resultados principalmente al efecto de dispersión de plasma. De hecho, más tarde se puso de manifiesto la presencia de varios factores limitantes y, más recientemente, se estimó que el valor del coeficiente χ(2) debía encontrarse en torno a varios pm/V. El trabajo desarrollado en esta tesis tiene como objetivo contribuir a impulsar el campo de silicio deformado mediante la investigación y el abordaje de dichos factores limitantes para, de esta fora, conseguir un efecto Pockels eficiente. Además, las características de captura de carga libre observadas en las estructuras de silicio deformado se han explotado para desarrollar un dispositivo fotónico no volátil. / [CA] En l'última dècada, la plataforma de silici ha emergit com la plataforma per excelència per a desenvolupar circuits fotònics integrats a causa de la seua versatilitat i la possibilitat de miniaturització i d'una producció de baix cost i a gran escala compatible amb els sistemes CMOS ("complementary metall-oxide semiconductor"). La conversió de senyals elèctrics a alta velocitat en senyals òptics és una funció crítica hui dia tant per al processament de dades com en l'àmbit de les telecomunicacions. La forma més eficaç d'implementar una modulació electro-òptica ultra-ràpida actualemente es basa en l'efecte *Pockels, que de fet,es troba en el cor dels moduladors comercials basats en el niobato de liti i polímers. No obstant això, la implementació d'aquesta funcionalitat es veu impedida en la plataforma de silici degut a la simetria d'inversió de la xarxa cristal·lina del silici. En aquest context, el silici deformat va sorgir fa més d'un decenni com una solució revolucionària per a trencar aqueixa centrosimetría i, d'aqueixa manera, fer emergir no-linealitats de segon ordre en el propi silici. No obstant això, malgrat els encoratjadors resultats inicials, estudis posteriors van qüestionar l'origen de la resposta obtinguda, atribuint-la principalment a aquest efecte de dispersió de plasma. De fet, més tard es va posar en relleu la presència de diversos factors limitants i, més recentment, es va estimar un valor de χ(2) en el rang de diversos pm/V. El treball desenvolupat en aquesta tesi té com a objectiu contribuir a impulsar el camp de silici deformat mitjançant la investigació i l'abordatge d'aquests factors limitants per a aconseguir un efecte Pockels eficient. A més, les característiques de captura de càrrega lliure observades en les estructures de silici deformat s'han explotat per a desenvolupar un dispositiu fotònic no volàtil. / [EN] In the last decade, silicon has emerged as the platform of choice for developing photonic integrated circuits due to its versatility, small footprint and the possibility of a low cost, large-scale CMOS compatible production. The conversion of high-speed electrical signals into optical digital data is a critical function for modern data communication technology. The most effective way for enabling ultra-fast electro-optical modulation is currently based on the Pockels effect, which is the basis of commercial modulators based on lithium niobate and polymers. However, the implementation of such functionality is prevented in the silicon platform due to the inversion symmetry of the silicon lattice. In this context, strained silicon emerged more than a decade ago as a revolutionary solution for breaking that centrosymmetry and, thus, allowing Pockels effect in the silicon material itself. However, despite the encouraging results from initial findings, following studies questioned the origin of the measured electro-optic response. In fact, the presence of several limiting factors was also later highlighted and a rather low strain induced χ(2) in the range of several pm/V was more recently estimated. The work developed on this thesis aims at contributing to push forward the strained silicon field by investigating and tackling such limiting factors to enable an efficient Pockels effect. Furthermore, the trapping properties observed in strained silicon structures have been exploited to develop a non-volatile photonic device. / Olivares Sánchez-Mellado, I. (2021). Development of Photonic Devices Based on the Strained Silicon Technology [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/167055

Ces travaux de thèse portent sur l’étude de différents phénomènes non-linéaires ayantlieu dans le domaine térahertz (THz) au sein de cristaux de structure zinc-blende.En premier lieu, nous avons mis en place au laboratoire deux sources de rayonnementTHz intense, aux caractéristiques temporelles et spectrales bien distinctes. La premièrerepose sur le redressement optique d’une impulsion laser de durée femtoseconde dansun cristal de niobate de lithium, et la seconde est, quant à elle, basée sur la créationd’un plasma par focalisation d’un champ optique compos´e de l’impulsion fondamentalede pompe et de son second harmonique. Ces deux sources permettent de générer desondes THz dont l’amplitude est bien adaptée à la mise en oeuvre d’expériences d’optiquenon-linéaire.Nous avons ensuite caractérisé le comportement non-linéaire de cristaux de structurezinc-blende soumis à des champs THz intenses. Nous nous sommes ainsi intéressés àl’effet Pockels lors de l’interaction d’une impulsion THz intense et d’un champ optiquede faible intensité, dit sonde, au sein du matériau. Ceci nous a conduits à démontrerexpérimentalement et numériquement la possibilité de caractériser la phase spectrale del’impulsion sonde, à l’aide d’une technique équivalente au X-FROG. Nous avons égalementidentifié l’existence d’un processus non-linéaire dit de cascade, consistant en la générationde second harmonique induite par effet Pockels. Enfin, nous avons observé expérimentalementl’apparition d’un effet Kerr THz dans le cristal, nous permettant de déduire unevaleur moyenne de la susceptibilité non-linéaire du troisième ordre de ce matériau, `a l’aidede calculs théoriques et de simulations numériques. / This thesis project aims to study different non-linear processes in zinc-blende crystals,which take place in the terahertz (THz) range.First of all, two different light sources have been built in the laboratory, allowing us togenerate intense THz radiations with different temporal and spectral characteristics. Thefirst source is based on the optical rectification of a femtosecond laser pulse in a lithiumniobate crystal using the tilted pulse front technique, while the second one is based on aplasma, created through the focalization of a two-color femtosecond laser field. These twoTHz sources reach very high amplitudes, which allows us to study non-linear phenomenain the THz range.Among these, we have measured the non-linear behavior of zinc-blende crystals underintense THz radiation. We were particularly interested in the Pockels effect happeningduring the interaction of an intense THz field and a weak optical probe beam. This droveus to the experimental and numerical demonstration of a new method to characterize thespectral phase of the optical probe field. This method is equivalent to the X-FROG technique.We also identified a new non-linear phenomenon, consisting of the cascade of twosecond-order processes, namely the Pockels effect and the Second Harmonic Generation.Finally, we experimentally observed some THz Kerr effect in a gallium phosphide crystal,which allowed us to calculate an average value of its third-order non-linear susceptibility,thanks to theoretical considerations and simulations.

CdTe and CdZnTe are promising materials for room temperature semiconductor X-ray and gamma ray detectors. The accumulation of a space charge at deep energy levels due to a band bending at contacts with Schottky barriers and due to trapped photogenerated charge may result in time dependent change of charge collection efficiency in CdTe and CdZnTe detectors known as polarization effect. This thesis is mainly focused on a study of electric field profiles in detectors under dark and high photon flux conditions simulating detector operation using crossed polarizers technique exploiting the electro-optic (Pockels) effect. It also deals with a study of deep levels responsible for the polarization and influence of contact metals on charge accumulation. Several experimental results are supported by theoretical simulations. The measurements were performed on three sets of samples equipped with different contact metals (Au, In) cut from three different n-type CdTe and CdZnTe materials. Energy levels were detected using methods based on the Pockels effect and discharge current measurements. Detailed study of internal electric field profiles has revealed a fundamental influence of near midgap energy levels related to crystal defects and contact metals on the polarization in semiconductor detectors under high radiation...

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O trabalho tem por objetivo o estudo e o desenvolvimento de interferômetros recuperadores com baixa tensão de meia onda utilizando moduladores eletro-ópticos para serem aplicados em sistemas Interferométricos de luz branca. Ele dá continuidade às pesquisas do autor em seu mestrado, em que foi desenvolvido e testado um sistema de sensoriamento eletro-óptico capaz de medir diretamente tensões de até 69,4 kVRMS. Desta forma aperfeiçoa-se o sistema de processamento de sinais ópticos desenvolvendo um novo interferômetro recuperador, baseado em óptica integrada. Para o desenvolvimento do tema proposto, inicialmente foi feito uma revisão da literatura/bibliografia, baseada em livros, artigos e teses, visando identificar o \"estado da arte\" relacionado aos moduladores eletro-ópticos para definir o tipo de modulador mais adequado à aplicação em vista. O estudo resultou na escolha de um componente em óptica integrada que foi aplicado numa configuração inédita em um protótipo de transformador de potencial óptico para medição de elevados níveis de tensão elétrica. As características de desempenho deste protótipo foram comparadas com as do protótipo previamente construído. Como resultado deste trabalho, amplia-se o conhecimento e fixa-se em âmbito nacional o domínio sobre as técnicas de construção de interferômetros recuperadores baseados em óptica integrada aplicáveis à recuperação de sinais ópticos em sistemas interferométricos para medição de altas tensões. / This work has as objective the study and development of low half-wave voltage recovery interferometers using electro-optical modulators to be applied to white light interferometric systems. This work is a continuation in the research carried out by the author to obtain his master degree, in which it was developed and tested an electro- optic sensing system capable to measure direct voltage to 69.4 kVrms. In the present work the optical signals processing system is improved by developing a new recovery interferometer based on integrated optics. To develop the proposed subject, initially a review of the literature, based on books, articles and thesis, has been done aiming to identify the State of the Art related to electro-optic modulators and helping to define the most suitable type of modulator for the desired application. The study resulted in the selection of an integrated optical device arranged in an unpublished configuration that was applied to a prototype of optical voltage transformer, intended to measure high voltage levels. The performance of this prototype was compared with a previous version. The results of this work increase the knowledge of the construction techniques of recovery interferometers based on integrated optic devices applicable to the recovering of optical signals in interferometric systems for high voltage measurement.