The experimental setup which consisted of the Jarrell-Ash Ebert type scanning monochromator, the Hamamatsu Si PIN Photodiode, a PC connected ADC card and a Tungstenstriplamp operated at different temperatures was assembled. The different parts needing calibration were calibrated with spectral response calibration techniques suitable for our purposes and connected to the experimental setup in a proper way. Spectral response calibrations and transmission measurements in the range 450-800 nm were carried out.

This thesis describes the fabrication and characterization of GaN homojunction visible-blind ultraviolet (UV) p-i-n avalanche photodiodes (APDs) grown by metalorganic chemical vapor deposition (MOCVD) on free-standing bulk GaN substrates. The objective of this research is to develop GaN UV p-i-n APDs with high linear-mode avalanche gains and the Geiger-mode operation for single photon detection. Low noise, high responsivity, and high detectivity are also required for fabricated APDs used as photodiodes in the photovoltaic mode (zero bias) and the photoconductive mode (low reverse bias). High material defect density and immature fabrication technology have hampered the development of III-nitride APDs in the past. In this thesis, sidewall leakage reduction methods have been developed to achieve significant improvement in dark current density, noise performance, and photo detection performance. A record linear-mode avalanche gain > 10⁵ for GaN APDs was demonstrated at λ = 360 nm. The first Geiger-mode deep UV (DUV) APD using front-illuminated homojunction p-i-n diode structure on a free-standing bulk GaN substrate was also measured with single photo detection efficiency (SPDE) of 1.0 % and dark count probability (DCP) of 0.03 at 265 nm. The performance of fabricated homojunction GaN p-i-n photodiodes was also evaluated in the photoconductive mode as well as the photovoltaic mode. For an 80-µm-diameter device biased at - 20 V (in the photoconductive mode) the dark current density is lower than 40 pA/cm² which is the lowest value achieved for any III-nitride photodiode so far. Its responsivity is 0.140 A/W at 360 nm with an ultraviolet-visible rejection ratio of 8×10³. The room-temperature noise equivalent power is 4.27×10 ⁻¹⁷ W-Hz-[superscript 0.5] and the detectivity D* is 1.66×10¹⁴ cm-Hz[superscript 0.5]-W ⁻¹ at - 20 V. The minimum detectable optical power is as low as 100 fW. They are among the best values reported for reverse-biased GaN p-i-n photodiodes to date.

Depuis une vingtaine d'années, le GRAMS et le CIMS travaillent en collaboration dans le domaine de l'imagerie médicale, plus précisément sur la tomographie d'émission par positrons destinée à la recherche préclinique sur petits animaux. Après le scanner TEP Sherbrooke en 1994 et le LabPET I commercialisé par Advanced Molecular Imaging (AMI) Inc., Gamma Medica Ideas et GE Healthcare au cours des années 2000, l'aspiration vers de meilleures performances est le moteur de la réalisation d'une nouvelle version : le LabPET II. L'augmentation importante du nombre de détecteurs, nécessaire pour atteindre une meilleure résolution spatiale, amène de nouveaux défis autant sur le plan matériel que logiciel. Un des défis est de compenser les disparités en gain des détecteurs à base de photodiodes à avalanche (PDA) qui engendrent des différences intercanaux. Le but de ce projet de maîtrise est de développer et d'implémenter un algorithme capable de corriger ces différences de façon automatisée.

Over 90% of traffic accidents are caused by human error. Therefore, the realization of autonomous driving could save countless lives and drastically reduce the associated financial expenses. Moreover, the collective behavior of self-driving cars would avoid traffic jams and thus reduce fuel consumption and greenhouse gas emissions. The majority of concepts is based on Light Detection And Ranging (LiDAR), which is the most precise method to measure distances. Matched to the 95% of commercial LiDAR systems based on laser wavelengths of mostly 905nm, siliconbased photo sensors are used. Avalanche photo diodes (APD) are the only sensor solution in mass production [6]. Due to an internal multiplication mechanism based on impact ionization, high signal-noise-ratios (SNR) are achieved and provide the required resolution of low signals from more than 100m distant targets. Currently none of the LiDAR technologies meet the reliability requirements of the automotive industry concerning the aging of installed components. Consequently, autonomous driving cannot yet be realized for public use. Very little is known about the aging of APDs in general and nothing at all in the field of automotive LiDAR. In order to provide novel insights into APD aging that help designers to achieve more robust sensors and thus to enable a step closer to the realization of autonomous driving, it was the aim of this thesis prepared in the industrial environment to reveal the underlying physical aging mechanisms and their effects on the function of APDs in automotive LiDAR application. At first, a novel APD degradation model was developed encompassing a wide range of processes, treating numerous fundamental aspects of negative oxide charge generation and Si:SiO2 interface trap generation. So far, no model is known covering the kinetics of APD degradation comprehensively in such deep detail. Due to the feedback between degradation phenomena and sensor internal fields and currents, a coupled problem arose. It was tackled by a sophisticated numerical iteration approach which was tailor-made and solved this problem self-consistently in a tandem procedure combining the simulation of sensor degradation and the Silvaco Atlas device simulator. This led to novel insights into the APD degradation behavior. The generation of negative oxide charges was identified to cause a drift of the impact ionization rate in the sensor edge. The generation of interface traps promotes the accumulation of negative oxide charges by their supply of thermally generated dark current. In this way, degradation is about 14% faster. In order to reflect not only the causal relations of APD degradation, the model was calibrated on experimental degradation data. With the calibrated degradation model and its self-consistent simulation approach an elaborated powerful tool was available. Stress experiments have been performed on test sensors under a variation of operation conditions and on APDs. APDs of the studied design are currently tested and installed in automotive LiDAR modules. The entire set of experimental results found its complete physical interpretation in conjunction with the degradation model which achieved an excellent agreement. Thereby, numerous novel insights were revealed: The extent of degradation is induced by the properties of the sensors oxide layer. The degradation pace increases with temperature, voltage and intensity of illumination whereas the impact of temperature is particularly strong due to the significant participation of the dark current during degradation. The oxygen vacancy was proven to be the dominant trap in the oxide layer of the studied sensors. An empirical distribution of individual sensor properties was achieved. In some cases, the impact ionization rate in the sensor edge increased which indicates a major problem, as noise increases when the generation- recombination processes in the sensor become more pronounced during degradation. In order to estimate the impact of the degradation induced increase of noise on the LiDAR application, the empirical distribution of individual sensor properties was extrapolated to the tail where sensors are very prone to degradation. Furthermore, the available noise models were extended to cover the effect of degradation. Application of the calibrated APD degradation model revealed, that the APD noise is highly effected and even triples during aging. The origin was exclusively assigned to the edge contribution. There, the avalanche breakdown of the edge dark current caused by degradation is the main initiator. Consequently, for the first time ever, the signal-noise-ratio (SNR) degradation mode of APDs in LiDAR application was identified. During degradation, the SNR of small signals from 100m distant objects degrades to a value below 1, where even theoretically a resolution is impossible. Finally, the picture of APD degradation was completed by the estimation of lifetime. In the case of the most severe conditions in LiDAR operation, it amounts to only 1000 h, which falls much below the requirements of the automotive industry of several decades.

L’infrarouge proche (1.5-2μm) ou SWIR (Short Wavelength Infrared) est une région particulièrement adaptée à la mesure de gaz à effet de serre par lidar à absorption différen- tielle (DIAL). En effet, (i) cet intervalle spectral contient des raies d’absorption intenses pour les principaux gaz à effet de serre (CO2, CH4, H2O, etc.) (ii) le taux d’extinction lors de la propagation du faisceau laser y est faible (iii) c’est une région spectrale dite en sécurité oculaire. Bien qu’abordée avec les moyens existants (détection hétérodyne), la mesure DIAL dans le SWIR a longtemps souffert de l’absence de photo-détecteurs ultra-sensibles. Les développements récents (années 2000) portant sur les photodiodes à avalanche (APD) HgCdTe ont changé la donne. En effet, ces dernières présentent de remarquables qualités d’amplification car elles allient trois propriétés fondamentales : un faible excès de bruit, un très faible courant d’obscurité et des gains importants. De telles propriétés sont essentielles pour les applications reposant sur la détection de très faibles signaux et en particulier le lidar.Dans cette thèse, nous analysons les performances d’un détecteur monopixel (200 μm) à base d’APD HgCdTe (conçu sur mesure par le CEA-LETI) dans le cadre de mesures expérimentales de la concentration de CO2 atmosphérique par lidar DIAL. L’émetteur laser est également un prototype, précédemment développé au Laboratoire de Météoro- logie Dynamique. Il produit alternativement des impulsions de 10 mJ à deux fréquences contrôlées dans la plage 2050-2054nm, le tout à une fréquence de répétition de 2kHz. Grâce à l’association de ces deux technologies de pointe nous avons pu effectuer les pre- mières mesures DIAL utilisant la technologie HgCdTe APD.Les expériences menées nous ont permis de confirmer le remarquable niveau de per- formances en sensibilité attendu (75 photons de bruit par temps caractéristique d’une bande passante de 20 MHz) et soulignent le potentiel futur d’un tel capteur pour toutes les applications faible flux dans le SWIR. Concernant les mesures DIAL, nous avons ob- tenu expérimentalement une précision relative de 10-20 % sur la concentration en CO2 pour une mesure dans la couche limite avec une résolution de 100 m - 4 s sur une portée de 1.5km. Par ailleurs, l’analyse fine de la réponse impulsionnelle de la photodiode à avalanche révèle une dégradation notable du long term settling time lorsqu’on la pola- rise. Ce phénomène contraint la plage d’utilisation du capteur, ce que nous discutons en tenant ce comportement du détecteur dans une simulation lidar. / The Short Wavelength Infrared (SWIR) region (1.5-2 μm) is well adapted for diffe- rential absorption lidar technique (DIAL) for several reasons : (i) it covers absorption bands with suitable intensity for the main greenhouse gases (CO2, CH4, H2O, etc.) (ii) the extinction due to particles is low (iii) it belongs to the eye safe domain. However, one main drawback has long been the lack of efficient photodetectors for such frequencies. A major enhancement occurred in the early 2000s when it was understood that HgCdTe avalanche photodiodes (APD) present close to unity excess noise factor on top of high gain and very low dark current. These features make this technology an almost ideal amplifier, especially useful for ultra low flux applications such as lidar.In this thesis, we analyze the performances of a custom large diameter (200μm) monopixel HgCdTe-APD based detector (designed at CEA-LETI) in the framework of atmospheric CO2 measurements with the DIAL technique. The laser emitter, a custom solid-state Ho :YLF laser developed at the Laboratoire de Météorologie Dynamique, is tunable in the 2050-2054nm range and produces 10 mJ pulses at a repetition rate of 2kHz. This emitter is associated to a detection chain adapted to the HgCdTe APD based detector to provide the first atmospheric DIAL measurements using the HgCdTe APD technology.Experiments confirmed the outstanding sensitivity of the detector (75 noise photons per characteristic time given a 20MHz bandwidth) and highlight the huge potential of this technology for any application relying on low light flux detection in SWIR. With the system previously mentioned, we reach an precision of 10-20 % on CO2 mixing ratio for a time-space resolution of 100 m and 4 s for measurements in the atmospheric boundary layer. Regarding the detector impulse response, we have shown evidence of a negative influence of reverse bias on the long term settling time of the APD. This phenomenon limits the dynamic range of useful signals and contraints the DIAL system. Thanks to numerical simulation taking into account this behaviour, we derive numerically expected biases on DIAL measurements.

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Particle suspension is a phenomenon when solid particles get trapped in a liquid. This phenomenon is a common occurrence in the water treatment industry. It is typically measured continuously throughout the treatment process to ultimately ensure high water-quality. Cerlic Controls AB specializes in developing sensors for the water treatment industry and have been doing so since 1977. Cerlic Control's sensors are used within the various stages of water-purification. The type of sensor central to this project uses transmission of light to determine a concentration of suspended particles. This project describes the development-process for one of Cerlic Controls existing embedded systems. The embedded system is undergoing a modernization process where the electronics and software are updated to a more modern design. This report describes the improvements to the measurement range while maintaining the same or improved resolution. These improvements are mostly performed by modern electronics and more advanced signal processing techniques in comparison to the previous implementation. A large portion of the previous implementation's software was split over two embedded systems due to limitations in processing power. This modern version focuses on bringing these two systems into one. The sensor's microprocessor has been replaced with a more modern higher performance alternative which allows all computations to be performed in the sensor. Linearity and stability are key aspects defining system performance. Optical filters block a certain amount of light and are heavily used in verification of performance. Suspensions using activated carbon were also used to evaluate the measurement range. The results of the project were largely successful. An initial implementation was achieved with optimistic results, but further work must be done before the sensor is ready for use in industry.

VLSI miniaturization has created the need for high-density, low-cost, monolithically-integrated optical interconnects. High output power photodetectors are needed to directly drive load circuitry, which improves the noise performance and dynamic range of optical communications links by eliminating a post amplifier stage. Elimination of the post amplifier also reduces circuit cost and complexity. A new Si-Ge PIN waveguide photodiode with 31GHz bandwidth and 93% quantum efficiency at 1550nm has been developed by Yin et al., which was fabricated using standard CMOS processes on a Silicon substrate. This thesis demonstrates a method for improving the RF power extraction from these photodiodes by increasing the impedance of the load. An RF output power improvement of 5.5dB is obtained by increasing the load resistance from 50 ohms to 177 ohms with 15MHz modulation. The maximum obtainable RF power of all devices tested using 50 ohm and 100 ohm loads at 15MHz is 15.73dBm and 17.83dBm, respectively. The maximum obtainable RF power using a 177 ohm load for all devices tested is 17.67dBm, which is slightly smaller than that obtained with a 100 ohm load. A measurement procedure for RF power extraction at microwave frequencies is also described. Quarter-wavelength 70.71 ohm thin film coplanar waveguides are designed to transform 50 ohms to a higher impedance of 100 ohms for measurements of improved RF power extraction at 3GHz and 7GHz.

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