This thesis presents experimental work developing silicon nanocrystal based light emitting devices for silicon photonics. The chapters are organized as follows: In chapter 2, fabrication and characterization of silicon nanocrystal based devices are presented. In collaboration with Intel Corporation and Bruno Kessler Foundation and thanks to the support of European Commission through the project No. ICT-FP7-224312 HELIOS and through the project No. ICT-FP7-248909 LIMA, it is shown that layers and devices containing silicon nanocrystals can be formed in a production silicon-fab on 4 and 8 inch silicon substrates via PECVD and subsequent thermal annealing. Devices produced by single layer and multilayer deposition are studied and compared in terms of structural properties, conduction mechanisms and electroluminescence properties. Power efficiency is evaluated and studied in order to understand the relation between exciton recombination and electrical conduction. A band gap engineering method is proposed in order to better control carrier injection and light emission in order to enhance the electroluminescence power efficiency. In chapter 3, the power efficiency of silicon nanocrystal light-emitting devices is studied in alternating current regime. An experimental method based on impedance spectroscopy is proposed and an electrical model based on the constant phase element (CPE) is derived. It is, then, given a physical interpretation of the electrical model proposed by considering the disordered composition of the active material. The electrical model is further generalized for many kinds of waveforms applied and it is generalized for the direct current regime. At the end, time-resolved electroluminescence and carrier injection in alternate current regime are presented. In chapter 4, erbium implanted silicon rich oxide based devices are presented. The investigation of opto-electrical properties of LED in direct current and alternate current regime are studied in order to understand the injection mechanism and estimate the energy transfer between silicon nanocrystals and erbium. At the end a device layout and process flow for an erbium doped silicon nanocrystal based laser structure are shown. In chapter 5, some other applications of silicon nanocrystal are presented. An example of all-silicon solar cell is shown. The photovoltaic properties and carrier transport of silicon nanocrystal based solar are studied. At the end, the combination of emitting and absorbing properties of silicon nanocrystal based LED are used to develop an all-silicon based optical transceiver.

Porous silicon (Psi) and nanocellulose (NC) hydrogels are nanostructured materials with several properties that make them promising for drug delivery applications. In this work, Î2-carotene (BC) and clofazimine (CFZ) are used as model molecules to investigate the physical and chemical processes governing the interactions of hydrophobic molecules with both inorganic (Psi) and organic (NC) nanostructured carriers. Despite the large number of advantages, Psi does not perform well as carrier for BC, since it stimulates the molecule degradation even if its surface is carefully passivated. Furthermore, during the release experiments, BC tends to nucleate on Psi surface forming aggregates whose dissolution is much slower than the BC molecules release, thus they negatively impact on the control over the drug release. On the other hand NC hydrogels do not pose heavy issues to the release of lipophilic drugs, provided that a suitable surfactant (either Tween-20 or Tween-80) mediates the molecule solvation and its subsequent release into aqueous media. Moreover, NC gels protect BC from degradation much better than its storage in freezer or in organic solvent, making these carriers interesting for DD.

This thesis work presents the results of experimental studies on the gas transport properties of three polymer-based membrane systems: (i) amine-modified epoxy resins, (ii) epoxy resin nanocomposites containing Few Layer Graphene (FLG) nanoplatelets as dispersed fillers and (iii) nanocellulose-based membranes. The gas transport properties of the present membrane systems were studied by gas phase permeation techniques changing sample temperature and penetrant molecules; results were discussed in the framework of the free volume theory of diffusion, using information on the samples’ free volume structure as experimentally obtained by Positron Annihilation Lifetime Spectroscopy (PALS). Results evidenced that the transport properties of small penetrant molecules are controlled by the membranes’ free volume structure, which determines, in fact, the penetrant diffusion kinetics. The free volume of epoxy resins was changed by changing their crosslink density but maintaining same chemical environment for penetrant molecules: it was observed that, reducing the free volume structure, the gas diffusivity decreases but no relevant changes in the gas solubility occurred. The experimentally obtained fractional free volume values permitted to reproduce the measured diffusivity values and their variation with temperature, using equations provided by the free volume theory of diffusion. Increasing the amount of FLG fillers in epoxy-based nanocomposites, we observed a progressive gas permeability decrease, which was accompanied by a progressive reduction of their free volume. This correlation was attributed to the formation of constrained, gas-impermeable polymer regions at the filler-matrix interfaces. The thickness of these regions was evaluated by the reduction of the nanocomposites’ fractional free volume with respect to the free volume of the pure polymer matrix; its value permits to reproduce quantitatively the experimental permeation data of the nanocomposites at all examined temperatures, filler concentrations and test gases. Few micrometers thick nanocellulose films deposited on polylactic acid substrates act as impermeable barriers for CO2, O2, and N2 and reduce the D2 (deuterium) and He permeation flux by a factor of approx. 10^3. Penetrant transport through this biopolymer is controlled by the solution-diffusion mechanism and barrier properties are due to the extremely low penetrant diffusivity. The free volume in the nanocellulose coatings consists of interconnected elongated cavities with sub-nanometer cross-sectional size where the selective transport of the small size penetrants is due to sieving effects. D2 and He diffusion has thermally activated character and occurs in configurational regime.

Optical biosensors, and in particular label-free optical biosensors have become one of the most active and attractive fields within the biosensing devices. The portability and the possibility to set free from the laboratory settings gave a new hint for integrated photonic biosensors development and use in numerous applications. Integrated photonic sensors have shown very promising results, and in particular, devices like WGM resonators and interferometers are showing high sensitivities and miniaturization abilities, which allow the realization of an integrated complete lab-on-chip device. The main goal of this thesis is the development of an optical biosensor for the fast and comprehensive detection of carcinogenic Aflatoxin M1 (AFM1) mycotoxin. The acceptable maximum level of AFM1 in milk according to European Union regulations is 50 ng/L equivalent to 152 pM for the adults and 25 ng/L equivalent to 76 pM for the infants, respectively. Within a European Project named SYMPHONY, we develop an integrated silicon-photonic biosensor based on the optical microring resonators (MRR) and the asymmetric Mach-Zehnder Interferometers (aMZI). The sensing is performed by measuring the resonance wavelength shift in the MRR transmission or the phase shift of aMZI caused by the binding of the analyte to the ligand immobilized on the sensor surface. The experimental characterization of the bulk refractometric sensing of the devices is performed in a continuous flow. This characterization assesses the high resolution of both device types, which are able to resolve variations in the refractive index of the liquids with a limit of detection down to 10E-6 refractive index units (RIU). Furthermore, the SYMPHONY sensor optimization based on the Fab' and DNA-aptamer functionalization strategies is realized. It is therefore demonstrated, that the Fab' functionalization strategy provides more reproducible results with respect to the DNA-aptamer one. However, for both strategies, the specificity of the sensor functionalization to detect AFM1 molecules is achieved with respect to non-specific Ochratoxin molecules at high concentrations. In the final stage of the SYMPHONY project, the Fab'-based functionalized aMZI sensor is tested with real milk samples (eluates) prepared in the SYMPHONY system that consists of the three main modules: the defatting module, the concentrator module and the sensor module. The system calibration yields the minimum concentration of AFM1 at 40 pM to be detectable. The detection of the ligand-analyte binding in real-time enabled the study of the kinetics of the binding reaction, and we measured for the first time the kinetic rate constants of the Fab'-AFM1 interaction with our sensors. Finally, a MRR based affinity biosensor is developed dedicated to the biotinylated BSA - anti-biotin binding study. An affinity constant of 10E6 1/M is measured. The sensor is successfully regenerated up to eight times by applying a longer incubation period.

X-ray photon correlation is used to probe the dynamics of the strong glass former boron trioxide and of a series of alkali borate glasses, (M2O)x(B2O3)1-x where M is the alkali modifier (M=Li, Na and K). The decay times τ of the obtained correlation functions in B2O3 are consistent with visible light scattering results and independent of the incoming beam intensity in the undercooled liquid phase; are instead temperature independent and show a definite dependence on the X-ray beam intensity in the glass. We are therefore witnessing an atomic dynamics induced by the X-ray beam. Furthermore, we clearly demonstrate that the value of τ is related to absorption by investigating a series of alkali borate glass with the same molar ratio and as a function of the alkali modifier. Finally, we highlight the role played by the structure in the X-ray induced dynamics by studying a series of lithium borate glasses with different molar ratios, and by investigating the wave vector dependence. Despite the observed dynamics is clearly intensity dependent, we obtain very interesting information on glasses not available with other experimental techniques.

In this thesis, second order optical nonlinearities in silicon waveguides are studied. At the beginning, the strained silicon platform is investigated in detail. In recent years, second order nonlinearities have been demonstrated on this platform. However, the origin of these nonlinearities was not clear. This thesis offers a clear answer to this question, demonstrating that this nonlinearity does not originate on the applied strain, but on the presence of trapped charges that induce a static electric field inside the waveguide. Based on this outcome, a way to induce larger electric fields in silicon waveguide is studied. Using lateral p-n junctions, strong electric fields are introduced in the waveguides, demonstrating both electro-optic effects and second-harmonic generation. These results, together with a detailed modeling of the system, pave the way through the demonstration of spontaneous parametric down-conversion in silicon.

High order waveguide modes are nowadays of great interest for the development of new functionalities in photonics. Because of this, efficient mode couplers are required. In this thesis a new strategy for mode coupling is investigated, based on the interference arising from two coherent tilted beams superimposed in a star-coupler. Handling the high order modes allows to explore new processes within the photonics platform, as the intermodal four wave mixing. Intermodal four wave mixing is a new nonlinear optical process in waveguide, and it is here demonstrated on a silicon chip. Via intermodal four wave mixing it is possible to achieve a large and tunable frequency conversion, with the generation of photons spanning from the near to the mid infrared. The broadband operation of this process is of interest for the field of quantum photonics. Single photon sources are the main building block of quantum applications, and they need to be pure and efficient. Via intermodal four wave mixing, it is here demonstrated the generation of single photons above 2000 nm heralded by the idler at 1260 nm. Thanks to the discrete band phase matching of this nonlinear process, high purity single photons without narrow band spectral filters are demonstrated. Intermodal four wave mixing enables a new class of classical and quantum sources, with unprecedent flexibility and spectral tunability. This process is particularly useful for the developing field of mid infrared photonics, where a viable integrated source of light is still missing.

The NEXT experiment is one of the most innovative ones looking for the neutrinoless double beta decay, which finding will answer one of the most important questions in the last years physics: is the neutrino its own antiparticle? Or in other words, is it a Majorana particle? With that purpose NEXT uses a TPC (Time Projection Chamber) filled with enriched xenon gas at high pressure, and two photosensors planes, one on each end. The first plane contains PMTs (PhotoMultiplier Tube), that collect the light emitted by the xenon when an event happens and precisely measures its energy. The second plane is a SiPM (Silicon PhotoMultiplier) matrix that allows to 3D-reconstruct the event track. Both planes together allows NEXT to have a great background rejection, which makes a difference with the other experiments aiming for the neutrinoless double beta decay. In addition, SiPMs are a new technology which nowadays is evolving to, in the future, displace the classical PMTs. For that reason the study of these sensors starts from zero, as there were not previous uses as pixel-tracking, and lead a new path in the physics detectors, for both high and low energy. This thesis is focused on the study and design of the electronics involving the tracking plane, which includes some technical solutions related also with mechanical issues. From the sensors placed inside the detector, the SiPMs, to the front-end electronic boards, there are few elements on the chain; as the support boards for the SiPMs which must satisfy severe outgassing and radiopurity levels. Also the inner and outer cabling has been designed, focusing on obtaining the best signal-noise ratio; and also the feedthrough for the tracking plane, which solved at low cost the huge problem of taking out about 4000 lines from the pressurized xenon to the outside. Finally, one of the most important elements on this chain and the one that this thesis is focused on, is the front-end board. Starting with the experience acquired with the first prototype, NEXT-DEMO, the electronics have been improved, able to condition, integrate and digitize the signals from all the tracking plane SiPMs; allowing the further acquisition and processing through an ATCA-based system (Advanced Telecommunications Computing Architecture). All the elements designed have been produced and assembled on the NEW detector, a large-scale prototype of the final detector, placed at the Laboratorio Subterra'neo de Canfranc, an underground laboratory at the aragonese Pyrenee. / El experimento NEXT es uno de los más innovadores en la búsqueda de la desintegración doble beta sin neutrinos, cuyo hallazgo daría con la respuesta a una de las cuestiones más importantes de la física en los últimos años: ¿es el neutrino su propia antipartícula? O dicho de otro modo, ¿es una partícula de Majorana? Para ello NEXT hace uso de una TPC (Time Projection Chamber) llena de gas xenón enriquecido a alta presión, y con dos planos de fotosensores, uno en cada extremo. El primero de ellos está formado por PMTs (Photo Multiplier Tube), que recogen la luz generada por el xenón cuando ocurre un evento, y miden la energía de éste. El segundo consiste en una matriz de SiPMs (Silicon PhotoMultipliers) que permiten reconstruir tridimensionalmente la traza de dicho evento. El conjunto de ambos planos de fotosensores otorga al experimento NEXT un gran rechazo a eventos de fondo, lo que marca la diferencia con otros experimentos en busca de la desintegración doble beta sin neutrinos. Además, los SiPMs son una tecnoloía de reciente aparición que en la actualidad está evolucionando a grandes pasos para, en un futuro, desplazar a los fotomultiplicadores clásicos. Por ello el estudio de estos fotosensores parte prácticamente desde cero, ya que no existen aplicaciones previas de su uso como pixel-tracking, y ha permitido abrir un nuevo camino en los detectores de física, tanto de alta como baja energía. Esta tesis doctoral tiene como objetivo el estudio y diseño de la electrónica involucrada en el plano de reconstrucción de trazas, y que involucran en menor medida dar solución a problemas técnicos de aspecto mecánico. Partiendo de los sensores ubicados dentro del detector, los SiPMs, hasta las tarjetas de front-end, se incluyen varios elementos de la cadena; como son las tarjetas empleadas como soporte para los SiPM en el interior de la cámara, las cuáles deben cumplir rigurosas medidas de radiopureza y degasificación. También se ha diseñado el cableado tanto interno como externo, haciendo énfasis en conseguir la mayor relación posible señal-ruido; y el pasamuros específico para el plano de reconstrucción de trazas, el cual ha resuelto a bajo coste el problema de extraer casi 4000 líneas desde la zona de xenón a alta presión hasta el exterior. Por último, uno de los elementos más importantes de esta cadena y en el cuál se centra principalmente esta tesis, es la tarjeta de front-end. Partiendo de la experiencia adquirida del primer prototipo del experimento, NEXT-DEMO, se ha perfeccionado una electrónica capaz de tratar, integrar y adquirir las señales de todos los SiPM del plano de reconstrucción de trazas, permitiendo su posterior adquisición y procesado mediante un sistema basado en la estructura ATCA (Advanced Telecommunications Computing Architecture). Todos los elementos diseñados han sido ensamblados y puestos en marcha en el detector NEW, un prototipo a gran escala del detector final, que está ubicado en el Laboratorio Subterráneo de Canfranc, en el Pirineo Aragonés. / L'experiment NEXT és un dels més innovadors en la recerca de la desintegració doble beta sense neutrins, i aquesta troballa donaria amb la resposta a una de les quèstions més importants de la física en els últims anys: és el neutrí la seua pròpia antipartícula? O dit d'una altra manera, és una partícula de Majorana? Per açò NEXT fa ús d'una TPC (Time Projection Chamber) plena de gas xenó enriquit a alta presió, i amb dos plànols de fotosensors, un a cada extrem. El primer d'ells està format per PMTs (Photo Multiplier Tube), que arrepleguen la llum generada pel xenó quan ocorre un esdeveniment, i mesuren l'energía d'aquest. El segon consisteix en una matriu de SiPMs (Silicon PhotoMultipliers) que permeten reconstruir tridimensionalment la traça d'aquest esdeveniment. El conjunt de tots dos plànols de fotosensors atorga a l'experiment NEXT un gran rebuig a esdeveniments de fons, la qual cosa marca la diferència amb altres experiments a la recerca de la desintegració doble beta sense neutrins. A més, els SiPMs so'n una tecnología de recent aparició que en l'actualitat està evolucionant a grans passos per a, en un futur, desplaçar als fotomultiplicadors clàssics. Per això l'estudi d'aquests fotosensors part pràcticament des de zero, ja que no hi ha aplicacions prèvies del seu ús com a pixel-tracking, i ha permés obrir un nou camí en els detectors de física, tant d'alta com de baixa energia. Aquesta tesi doctoral té com a objectiu l'estudi i diseny de l'electrònica involucrada en el plànol de reconstrucció de traces, i que involucra en menor mesura donar solució a problemes tècnics d'aspecte mecànic. Partint dels sensors situats dins del detector, els SiPMs, fins a les targetes de front-end, s'inclouen diversos elements de la cadena; com són les targetes emprades com a suport per als SiPMs a l'interior de la càmera, les quals han de complir rigoroses mesures de radioactivitat i degasificació. També s'ha disenyat el cablejat tant intern com extern, fent èmfasi en aconseguir la major relació possible senyal-soroll; i el passamurs específic per al plànol de reconstrucció de traces, el qual ha resolt a baix cost el problema d'extraure quasi 4000 línies des de la zona de xenó a alta presió fins a l'exterior. Finalment, un dels elements més importants d'aquesta cadena i en el qual es centra principalment aquesta tesi, és la targeta de front-end. Partint de l'experiència adquirida del primer prototip de l'experiment, NEXT-DEMO, s'ha perfeccionat una electrònica capaç de tractar, integrar i adquirir les senyals de tots els SiPM del plànol de reconstrucció de traces, permetent la seua posterior adquisició i processament mitjançant un sistema basat en l'estructura ATCA (Advanced Telecommunications Computing Architecture). Tots els elements disenyats han sigut muntats i engegats en el detector NEW, un prototip a gran escala del detector final, que està situat en el Laboratorio Subterráneo de Canfranc, al Pirineu Aragonés. / Rodríguez Samaniego, J. (2017). Study and design of the front-end and readout electronics for the tracking plane in the NEXT experiment [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86285

Light measurements are widely used in physics experiments and medical applications. It is possible to nd many of them in High{Energy Physics, Astrophysics and Astroparticle Physics experiments and in the PET or SPECT medical techniques. Two different types of light detectors are usually used: thermal detectors and photoelectric effect based detectors. Among the rst type detectors, the Bolometer is the most widely used and developed. Its invention dates back in the nineteenth century. It represents a good choice to detect optical power in far infrared and microwave wavelength regions but it does not have single photon detection capability. It is usually used in the rare events Physics experiments. Among the photoelectric effect based detectors, the Photomultiplier Tube (PMT) is the most important nowadays for the detection of low-level light flux. It was invented in the late thirties and it has the single photon detection capability and a good quantum efficiency (QE) in the near-ultraviolet (NUV) and visible regions. Its drawbacks are the high bias voltage requirement, the diculty to employ it in strong magnetic field environments and its fragility. Other widely used light detectors are the Solid-State detectors, in particular the silicon based ones. They were developed in the last sixty years to become a good alternative to the PMTs. The silicon photodetectors can be divided into three types depending on the operational bias voltage and, as a consequence, their internal gain: photodiodes, avalanche photodiodes (APDs) and Geiger-mode detectors, Single Photon Avalanche Diodes (SPADs). The first type detector does not have internal gain, thus its signal is proportional to the number of incoming photons that are converted in electron-hole pairs. The detector and the read-out circuit noises limit the detector sensitivity to, at least, some hundreds of photons. The APD exploits the impact ionisation effect to have an internal gain up to some hundreds or more. The internal gain allows the detector to improve the performance with respect to a similar area photodiode reducing the sensitivity limit to some tens of photons. Operating the APDs with a bias voltage larger than the breakdown one, the Geiger-mode operation range can be reached. In this case, the detectors have a very high gain, in the order of (10^5-10^7), but their signal is not proportional to the number of the incoming photons, it is always the same. The SPAD (or GM-APD) is a typical Geiger-mode silicon detector. It has the single photon detection capability as the PMT, due to the high gain, but its signal is digital: it is fired or not by the incoming photons. The capability to give a signal proportional to the number of photons is lost in a SPAD. To recover this property, a matrix of independent SPADs connected in parallel is built. These matrices are called Silicon Photomultipliers, SiPMs (or Multi-Pixel Photon Counters, MPPCs). In a typical SiPM, the output signal is the sum of the SPAD ones, thus, although the digital nature of the SPAD signal, it is analogue and ranges from zero to the maximum number of cells composing the matrix. The detector response can be considered linear if the number of incoming photons is much smaller than the total number of cells because the probability that two photons arrive on the same cell is negligible. Main features of the SiPMs are the low bias voltage (<100 V typically), a high Photo-Detection Efficiency (PDE) in NUV and visible range (usually larger than the PMT QE), compactness, insensitivity to magnetic elds and high internal gain. The noise sources are the Dark Count Rate (DCR), the optical Cross-talk (CT) and the Afterpulsing (AP). The first is called primary noise and mainly depends, at room temperature, on the thermal generation of electron-hole pairs that can travel to the high-field region triggering a cell. The others are collectively called correlated noise because they can happen only after a primary signal, caused both by a photon or by a spontaneous carrier generation. In this thesis, the focus is on the characterisation of one SiPM technology produced in Fondazione Bruno Kessler (FBK) in Trento, Italy, named NUV-SiPMs. This technology, implementing the p-on-n concept, showed, from the beginning, a high PDE spectrum peaked in the NUV to violet region exceeding the 30 %, a very low DCR, typically below 100 KHz/mm^2 in the operating voltage range, and a total correlated noise probability under the 50 %. In the last years, the technology was developed modifying the silicon wafer substrate properties, reducing the delayed correlated noise probabilities, and adopting the so-called High-Density concept. In this last version, named NUV-HD, a new layout, with a narrower border region around the cell active area and deep trenches to electrically and optically isolate the cells, is employed. The first improvement has a direct influence on the PDE because it increases the Fill Factor (FF), the ratio between the active to the total cell area. The second layout change reduces the probability that a secondary photon can travel from a cell to a neighbouring one, reducing the cross-talk probability. Possible applications of the NUV-HD devices are: medical application (e.g. the Time of Flight PET, ToF-PET, scanners), the rare events Physics experiments (e.g. NEXT and DarkSide) and Astroparticle Physiscs experiments (e.g. the Cherenkov Telescope Array Observatory, CTA). The ToF-PET scanners are promising medical techniques with the goal of improving the spatial resolution of the classical PET scanners measuring the gamma rays time of flight. For this reason, these scanners require very fast photodetectors with coincidence time resolution (CTR) less or equal to 100 ps. NEXT and DarkSide are low temperature experiments with the main goal of observe rare events as the neutrinoless double beta decay and the Dark Matter particles. Due to the signal rarity, the detector noise requirements are very stringent. CTA will be a future ground-based Imaging Atmospheric Cherenkov Telescope (IACT) observatory, with the goal to track very high energy cosmic gamma rays, up to hundreds of TeV, to their galactic sources. It will consist of two matrices of telescopes of different type and size, each one having a camera. In the small size telescopes, the possibility to use the SiPMs to build the camera is under investigation. Since the cosmic gamma rays are detected through the secondary Cherenkov photons, produced by the accelerated electrons in the Earth atmosphere, the camera photosensors must have a very high detection efficiency from 300 nm to 600 nm, and, possibly, a low sensitivity in the NIR region to reject the night sky background. In addition, they must have good timing properties and high granularity. To fully characterise the SiPM, measurements of signal properties, noise parameters and PDE are needed. The set-ups and analysis of the characterisation procedure are fully described. In particular, the optical set-up, with its calibration procedures, and the analysis methods, with the definition of the possible uncertainty sources, are the central point of this work. During the dark characterisation, the SiPM is enclosed in a light-tight climatic chamber. An oscilloscope acquires and sends to a PC software millisecond-long SiPM waveforms. The software implements a Differential Leading Edge Discriminator (DLED) algorithm to better distinguish the SiPM pulses with time separation larger than a few nanoseconds. This analysis allows to count the primary pulses, due to the thermal/tunnelling excitations, obtaining the DCR, and measure the correlated noise probabilities. In addition, signal parameters as amplitude, gain and cell recharge time are measured. The PDE measurements require a set-up in which the number of impinging photons to the device is precisely known. For this reason, a compact set-up, consisting of an integrating sphere inside a light-tight box, a series of LEDs with peak wavelength ranging from NUV to NIR, fully characterised before use, a monochromator, equipped with a tungsten lamp, and a transparent optical fibre, was developed. Along with the set-up, a light calibration procedure, taking into account different uncertainty sources (LED wavelength shift, light uniformity at the device position, etc.), was also developed. Three different analysis techniques can be used to obtain the technology PDE. Each technique has its own benets and error sources. The equivalence among the different methods is shown. Moreover, measuring the PDE on SPADs with the same layout of single SiPM cells, identical results are obtained. This fact shows the equivalence between the single cell device and its larger counterpart, opening the possibility to measure the PDE of a new technology on SPADs. This is a very important result because the SPAD is a simpler device, with lower correlated noise, because it has no CT, and negligible primary one, often less than 1 kHz. Measurements are more precise, faster and it is possible to apply larger bias voltage, obtaining more information on the technology in such conditions at which no SiPM can be tested any more. A rst version NUV-HD technology characterisation is shown. In this version, the NUV-HD SiPMs have cell pitch ranging from 25 um to 40 um. A typical primary noise lower than 100 KHz/mm^2 and a delayed correlated noise probability less than 5 % are measured, up to 10 V of overvoltage. In the same bias voltage range, a direct CT probability lower than 45 % is measured in the largest cell devices (25 % in the smallest ones). The PDE spectrum has the expected shape with the maximum in the NUV-violet region. A maximum value exceeding the 60 % is measured in the largest cell devices (45 % in the smallest ones). To investigate possible variations of the measured features on the wafer, devices taken from different wafer points are measured and compared finding no difference but the primary noise. This parameter shows a variation by a factor up to about three on the wafer level. To compare the different cell devices, all the measured parameters are plotted as a function of the peak PDE, about 400 nm. During this comparison, the smallest device reveals worse than the others having a larger noise, both primary and correlated, at the same PDE value. The other three devices are comparable within the measurement errors. From the PDE measurements, a comparison between the measured FF and the expected one, as dened by the design, is obtained. In the smallest cell device, this comparison shows an unexpected discrepancy leading to the possibility that the expected FF is larger than the effective one. This possibility is investigated in the last part of this thesis in which a complete study of the factors contributing to the PDE is shown. This study is performed on a new NUV-HD version employing a photodiode with equal dopant prole of the SiPMs, a circular SPAD having 100 % FF and a square one with 35 um cell size and a nominal FF equal to 81 %. A developed box model is used to describe the electric eld inside the cell. The calculated effective FF is always different from the expected one. The reason of the measured difference is the electric field transition from the constant high value to zero occurring at the active area border region. This partially efficient region has an effect similar to an added completely ineffective region of 1-1.5 um size inside the expected active area. The transition region effect is critical for the smallest cells because it strongly reduces the effective FF with respect to the design one. The study of the factors contributing to the PDE of the NUV-HD SiPMs is very important. Through the obtained results, it is confirmed that the technology QE is just maximised in the wavelength range of interest, NUV to blue, and, at the same wavelengths, the triggering probability saturation rate is very small allowing the detectors to reach the maximum PDE when biased with a few volts of overvoltage. This operating condition has also the effect to employ the detector having low noise, both primary and correlated one. The best solution to further improve the technology PDE is a redesign of the electric field border region to reduce the gap between the expected FF and the effective one. This is more important for the smallest cell devices in which the actual transition region effect reduces the PDE performance to about the 50-60 % of the expected values.

Proton therapy is a recent type of radiotherapy that uses high-energy proton beams, and more recently carbon ion beams, to benefit of their physical selectivity. The energy deposited by these particle beams is inversely proportional to their velocity. Therefore they release most of the energy at the end of their path into the tissue. The energy is deposited in a few millimeters, in a zone called the Bragg peak. Before and after the Bragg peak the energy deposition is minimal. The depth and the width of the Bragg peak depends on the beam energy and on the density of tissues located along the beam path. By setting the beam energy, the Bragg peak can be positioned in the tumor site, avoiding the healthy tissues. Because of the sharpness of the Bragg peak zone, proton therapy is advantageous for tumors located near to important body part, such as the brain, spine, and neck. The drawback is that small uncertainties on particle range can have a serious impact on treatment and limit the efficiency of the proton therapy. To obtain more effective treatments in proton therapy real-time range verifications are necessary to perform on-line corrections of the delivered treatment. Among different techniques presented in the literature, positron emission tomography (PET) and prompt gamma imaging (PGI) are the most promising methods for in vivo range verification. PET and PGI are indirect approaches to measure protons penetration depth inside patients because they aim to detect secondary particles resulting from the interaction between proton beams and tissue nuclei. PET imaging detects coincidence gamma rays due to the production of positron emitters and requires some minutes to achieve enough statistics to have a sufficient signal to noise ratio. PGI instead uses prompt gamma rays generated by de-excitation of target nuclei; the quantity of these rays and their temporal emission (few nanoseconds) allow to perform a range verification during treatment with the PGI. Several research groups are evaluating different approaches to realize a prompt gamma imaging system suitable for the use in clinical condition and the optimization of a gamma-ray detector for PGI is still ongoing. The Gammarad project works in this direction and aims to develop an high-performance and solid-state gamma ray detection module (GDM) with a slit camera design. The project is based on a collaboration among Fondazione Bruno Kessler (FBK, Trento, Italy), Politecnico di Milano (Milano, Italy), the Trento Institute for Fundamental Physics and Applications (TIFPA, Trento, Italy ), and the Proton Therapy Center of Trento (Italy). The project is divided into two parts. The first part focuses on the technological development of a gamma-ray imaging module. This module is composed by a gamma-ray detector, based on a solid-state silicon sensor, and an integrated circuit. They are assembled into a compact module with data and control systems. The second part of the project will be dedicated to the experimental validation of the system both in laboratory with radioactive sources and in a real environment, that of proton therapy. The most innovative part of the gamma-ray detector developed for the project is the photo-sensor used for the scintillation light readout. In traditional applications it is a photomultiplier tube (PMT). However, in recent years, Silicon Photomultiplier (SiPM) has become increasingly popular in a variety of applications for its promising characteristics. Among them, current-generation SiPMs offer high gain, high Photon Detection Efficiency (PDE), excellent timing performance, high count-rate capability and good radiation hardness. Due to these characteristics they are used as PMTs replacement in several applications, such as in nuclear medicine (PET), in high-energy physics (calorimeters), astrophysics (Cherenkov telescopes) and in others single-photon or few-photon applications. For its characteristics, the SiPM is also very promising for the scintillator readout in prompt gamma imaging and in high energy gamma-ray spectroscopy. Detectors for these applications must be compact, robust, and insensitive to the magnetic field. They have to provide high performance in terms of spatial, temporal, and energy resolution. SiPMs can satisfy all these requirements but typically they have been used with relatively low energy gamma rays and low photon flux, so manufacturers have optimized them for these conditions. Because of the limited number of micro-cells in a standard SiPM, 625 cells/mm^2 with 40 μm cells, the detector response is non-linear in high energies condition. Increasing the cell density is extremely important to improve the linearity of the SiPM and to avoid the compression of the energy spectrum at high energies, which worsens the energy resolution and makes difficult the calibration of the detector. On the other hand, small cells provide a lower Photon Detection Efficiency (PDE) because of the lower Fill Factor (FF) and as a consequence a lower energy resolution. Summarizing, the energy resolution at high energies is a trade-off between the excess noise factor (ENF) caused by the non-linearity of the SiPM and the PDE of the detector. Moreover, the small cell size provides an ultra-fast recovery time, in the order of a few of nanosecond for the smallest cells. A short recovery time together with a fast scintillator such a LYSO, reduces pile-up in high-rate applications, such as PGI. Based on the above considerations, the aim of this thesis is to develop an optimized gamma-ray detector composed of SiPMs for high-dynamic-range application, such as the scintillation light readout in prompt gamma imaging and in high-energy gamma-ray spectroscopy. SiPMs evaluated for the detector are High-Density (HD) and Ultra-High-Density (UHD) SiPM technologies recently produced at Fondazione Bruno Kessler (FBK). Instead of standard SiPMs, HD and UHD SiPMs have a very small micro-cell pitch, from 30 μm down to 5 μm with a cell density from 1600 cells/mm^2 to 46190 cells/mm^2, respectively. HD SiPMs are produced using a lithography technology with smaller critical dimensions and designed with trenches among SPADs. Small cells have a lower gain which helps to reduce correlated noise, such as After-Pulse and Cross-Talk. Trenches provide an optical and electrical cell isolation, and a smaller dead border around cells which increase the FF limiting PDE losses. UHD SiPMs push the limits of the HD technology even further, by reducing all the feature sizes, such as contacts, resistors and border region around cells. UHD SiPMs have hexagonal cells in a honeycomb configuration which generate a circular active area and a dead border around cells lower than 1 μm. The reduction of this dead boarder can improve the FF in smaller cells although it usually decrease with cell sizes. It is necessary understand how these significant layout changes affect the optical properties of SiPMs to evaluate which SiPM technology provides best performance in high-energy gamma-ray applications. In the first part of the thesis, I presents the characterization of HD and UHD SiPM technologies in terms of PDE, gain, Dark Count Rate, and correlated noise for the cell sizes between 30 and 7.5 μm. The most important markers of SiPMs performance in gamma-ray spectroscopy are however the energy resolution and the linearity when coupled to the scintillator for the detection of high-energy gamma-rays. A typical characterization of the energy resolution of SiPMs, coupled to scintillator crystals, is performed with radioactive source up to 1.5 MeV. However, PGI features gamma ray-energies up to 15 MeV which are not easily provided by the usual laboratory calibration sources. Extrapolating the behaviour of the detector from the "low" energy data is not correct and leads to unreliable data for calibration and performance estimation. Therefore, I developed a novel setup that simulates the LYSO light emission in response to gamma photons up to 30 MeV. A LED (emitting at 420 nm) is driven by a pulse generator, emulating the light emitted by a LYSO scintillator when excited by gamma rays. The pulse generator parameters (amplitude, duration, rise and fall time constants) are adjusted so that the LED emitted photons match the intensity and time distribution of the LYSO emission. The photon number in each light pulse is calibrated from the measurements at 511 keV obtained with a ^(22)Na source and a LYSO crystal coupled to the SiPMs. Using this LED setup I characterized the energy resolution and non-linearity of HD and UHD SiPMs in high-energy gamma-ray conditions. The second part of the thesis provides a detailed description of the scintillator setup and of the setup for the simulation of high-energy gamma-ray response, followed by the results of the characterization performing with these setups. Summarizing the results, the lowest non-linearity is provided by the technology with highest cell density, the RGB-UHD. For the 10 and 12.5 μm-cells we obtained values of 4.5% and 5% respectively at 5 MeV and 6 V over-voltage. On the other hand, we measured the best energy resolution of 2.6% and 2.3% at 5 MeV for the largest SiPM cells of 20 and 25 μm respectively, without the intrinsic term of the scintillator crystal and at 6 V over-voltage. This is due to the dependence of the energy resolution on the photon detection efficiency, which increases with the size of the SiPM cell. The optimal performance of the detector in high-dynamic-range applications, which depends on the several SiPM parameters, such as excess noise factor, photon detection efficiency, and cell sizes of the SiPM, is a trade off between non-linearity and energy resolution. At 5 MeV, the best trade-off for prompt gamma imaging application is reached by the 15 μm-cell. At 10 MeV the 12.5 μm-cell provides the best trade-off, because of the higher number of photons emitted by the scintillator. Furthermore, I distinguish the different components of the energy resolution (intrinsic, statistical, detector and electronic noise) as a function of cell sizes, over-voltage and energy, thanks to the combination of the scintillator and LED setups. The estimation of the intrinsic contribution of the scintillator crystal, coupled to the HD SiPMs, getting consistent results among the several cell sizes. On the basis of previous characterization, HD SiPMs with dimensions of 4x4 mm^2 and 15 μm-cell were chosen to produce the photo-detector module of the gamma camera, optimized for an energy range between 2 and 8 MeV. This module is a 8x8 array of SiPMs which is called tile. The production of the tile requires research on packaging techniques to solve two main challenges: the maximization of the photo-sensitive area and the application of a protective resin, transparent in the near UV to maximize light collection from the LYSO. After some R&D on packaging, I obtained a fully functional tile with 64 SiPMs with a fill factor, ratio between the photo-sensitive area and the total area, of about 86%. This fill factor is comparable to the values obtained when a Through Silicon Vias (TSVs) technique is used to connect SiPMs but without the high production cost and the additional fabrication process complexity of the TSV. It should be highlighted that packaging operations is very critical because it is necessary to produce a tile with all working SiPMs, since defective items can not be replaced in the tile. The last part of the thesis presents the packaging procedure that I have defined to produce photo-detector modules and the characterization of the photo-detector array in terms of energy resolution, position sensitive and non-linearity. The measurements on the tile were carried out jointly with the Gammarad partner of Politecnico di Milano, which provided the ASIC and DAQ for the readout. In conclusion, the R&D activity carried out during this thesis has provided to Gammarad project the final photo-detection module with state of the art performance for high-energy gamma-ray spectroscopy. The characterization of the module shows also a position sensitivity that matches with the SiPM dimensions, and a proper acquisition of high-energy gamma-ray events from 800 keV to 13 MeV. This module will be tested on beam in an experimental treatment room at the Proton therapy facility in Trento by the Gammarad project partners.