A theoretical model with experimental verification is presented to enhance the quantum efficiency of a superconducting single-photon detector without increasing the length or thickness of the active element. The basic enhancement framework is based on: (1) Utilizing the plasmonic nature of a superconducting layer to increase the surface absorption of the input optical signal. (2) Enhancing the critical current of the nanowires by reducing the current crowding at the bend areas through optimally rounded-bend implementation. The experimental system quantum efficiency and fluctuation rates per second are assessed and compared to the proposed theoretical model. The model originated from an accurate description of the different liberation mechanisms of the nano-patterned superconducting films (vortex hopping and vortex-antivortex pairing). It is built complimentary to the existing, well-established models by considering the effects of quantum confinement on the singularities' energy states. The proposed model explains the dynamics of singularities for a wide range of temperatures and widths and describe an accurate count rate behavior for the structure. Furthermore, it explains the abnormal behaviors of the measured fluctuation rates occurring in wide nano-patterned superconducting structures below the critical temperature. In accordance to this model, it has been shown that for a typical strip width, not only is the vortex-antivortex liberation higher than the predicted rate, but also quantum tunneling is significant in certain conditions, and cannot be neglected as it has been in previous models. Also it is concluded that to satisfy both optical guiding and photon detection considerations of the design, the width and the thickness of the superconducting wires should be carefully determined in order to maintain the device sensitivity while crossing over from the current crowding to vortex-based detection mechanisms.

Fluorescence lifetime imaging (FLIM) has the potential to provide rapid screening and detection of diseases. However, time-resolved fluorescence measurements require high-performance detectors with single-photon sensitivity and sub-nanosecond time resolution. These systems should also be compact, reliable, inexpensive, and easily deployable for laboratory and clinical applications. It is with these applications in mind that the development of single photon avalanche diodes (SPAD) and time-to-digital converter (TDC) prototype integrated circuits (IC) in standard digital CMOS have been pursued in this thesis. SPAD and TDC ICs were designed and fabricated in 130 nm IBM CMOS technology and then intensively studied. Several different SPAD pixels were modeled and designed, and the electro-optical performance was characterized and comparatively studied. By repurposing existing design layers of a standard CMOS process, the fabricated SPAD pixel test structures achieved up to 20× improvement of dark count rate (DCR) compared to previous designs. Optical measurements also showed up to 10× improvement in the detection limits for low-level light. Detailed dark noise characterization was performed at various temperatures using free-running and time-gated modes of operation. Optimal operating conditions were found for minimal afterpulsing effects. The SPAD’s capability to accurately measure fast fluorescence decays was also demonstrated in a practical setting with the lifetime measurements of two fluorophores, Rhodamine 6G and Ruby crystal, which have fluorescence lifetimes of approximately 4 ns and 3 ms, respectively. A fast and accurate TDC prototype circuit for time-correlated single-photon counting (TCSPC) applications was designed, fabricated and characterized. With a coarse-fine delay line architecture, the TDC size was reduced without compromising its linearity and jitter performance. Extensive characterization of the fabricated SPAD and TDC ICs shows that the measured performance met the stated design goals. / Thesis / Doctor of Philosophy (PhD)

Superconducting nanowire single-photon detectors (SNSPDs) are nanodevices usually made from thin niobium nitride (NbN) films. Operated at liquid helium temperature, they can exhibit high detection efficiency with low dark-counts associated with a fast response time and a low timing jitter. Covering a broad detection range from ultraviolet to mid-infrared, SNSPDs are a very attractive alternative to silicon or gallium arsenide based semiconductor detectors for fiber based telecommunication when single-photon sensitivity and high counting rates are necessary. Efficient packaging and fiber coupling of a SNSPD is in itself a real challenge and is often a limiting factor in reaching high system quantum efficiency. Our approach makes use of a controlled expansion alloy which has been adequately heat treated to enhance its characteristics for cryogenic operation. This insures the integrity of the optical coupling at cryogenic temperatures while done at room temperature. It also provides a good attenuation for electromagnetic interference due to the high relative permeability of the nickel-iron alloy. The small form factor of this pigtailed optical fiber package makes it versatile and could be easily integrated with a commercial cryogen-free system or simply dipped into a standard helium transport Dewar. We report on our theoretical and experimental methodology to evaluate the optical coupling quality and present the optoelectronic characterization of two devices packaged in this way. Electrical simulation is studied to understand the speed limitation factor inherent to these devices and preliminary speed and jitter measurements are reported.

Superconducting nanowire single-photon detectors (SNSPDs) are nanodevices usually made from thin niobium nitride (NbN) films. Operated at liquid helium temperature, they can exhibit high detection efficiency with low dark-counts associated with a fast response time and a low timing jitter. Covering a broad detection range from ultraviolet to mid-infrared, SNSPDs are a very attractive alternative to silicon or gallium arsenide based semiconductor detectors for fiber based telecommunication when single-photon sensitivity and high counting rates are necessary. Efficient packaging and fiber coupling of a SNSPD is in itself a real challenge and is often a limiting factor in reaching high system quantum efficiency. Our approach makes use of a controlled expansion alloy which has been adequately heat treated to enhance its characteristics for cryogenic operation. This insures the integrity of the optical coupling at cryogenic temperatures while done at room temperature. It also provides a good attenuation for electromagnetic interference due to the high relative permeability of the nickel-iron alloy. The small form factor of this pigtailed optical fiber package makes it versatile and could be easily integrated with a commercial cryogen-free system or simply dipped into a standard helium transport Dewar. We report on our theoretical and experimental methodology to evaluate the optical coupling quality and present the optoelectronic characterization of two devices packaged in this way. Electrical simulation is studied to understand the speed limitation factor inherent to these devices and preliminary speed and jitter measurements are reported.

Ce manuscrit présente mon travail de thèse portant sur le détecteur de photons niques electron-bpmbarded CMOS (ebCMOS) à haute cadence de lecture (500 images/seconde). La première partie compare trois détecteurs ultra-sensibles et leurs méthodes d'amélioration de la sensibilité au photon : le CMOS bas bruit sCMOS), l'électron-multiplying CCD (emCCD) à multiplication du signal apr pixel et l'ebCMOS à amplification par application d'un champ électrique. La méthode de mesure de l'impact intra-pixel des photons sur le détecteur ebCMOS est présentée. La seconde partie compare la précision de localisation de ces trois détecteurs dans des conditions extrêmes de très bas flux de phtons (<10 photons/image). La limite théoriques est d'abord calculée à l'aide de la limite inférieure de Cramér-Rao pour ces jeux de paramètres significatifs. Une comparaison expérimentale des trois détecteurs est ensuite décrite. Le montage permet la création d'un ou plusieurs points d'accès contrôlés en position, nombre de photons et bruit de fond. Les résultats obtenus permettent une comparaison de l'efficacité, de la pureté et de la précision de localisation des sources. La dernière partie décrit deux expériences réalisées avec la caméra ebCMOS. La première consiste au suivi des nano-cristaux libres (D>10 µm2/s) au centre Nanoptec avec l''équipe de Christophe Dujardin. La seconde s'intéresse à la nage de bactéries en surface à l'Institu Joliot curie avec l'équipe de Laurence Lemelle. L'algorithme de suivi de sources ponctuelles au photon unique avec l'implémentation d'un filtre de Kalman est aussi décrit. / This manuscript presents my thesis on the high frame rate (500 frames/second) single-photon detector electron-bombraded CMOS (ebCMOS). The first section compares three ultra-sensitive detectors and their methods for improving photon sensitivity : the CMOS low noise (sCMOS), the electron-multiplying CCD (emCCD) with signal multiplication by pixel and the ebCMOS with amplification by applied electric field. The method developped to detected single photon impacts with intra-pixel resolution on the ebCMOS sensor is presented. The second section compares the localization accuracy of these detectors in extreme conditions of very low photon flux (<10 photons/ frame). First the theoretical limit is calculated using the Cramér-Rao lower bound for significant parameter sets. An experimental comparaison of the detectors is then described. The setup provides of one or more point sources controlled in position, signal and background noise. The results allow a comparison of the experimental effectiveness, purity and localization accuracy. The last section describes two experiments with the ebCMOS camera. The first aims to track hundreds of quantum dots simultaneously at the Nanoptec center with the team of Christophe Dujardin. The second focuses on the swimming of bacteria at the surface at the Jolio Curie Institute with the team of Laurence Lemelle. The point sources tracking algorithm using single photons and the Kalman filter implementation developed for these experiments is alson described.

Thomson scattering from free electrons in a high-intensity laser focus has been widely studied analytically, but not many measurements of this scattering have been made. We measure polarization-resolved nonlinear Thomson scattering from electrons in a high-intensity laser focus using a parabolic mirror. The weak scattering signal is distinguished from background noise using single-photon detectors and nanosecond time-resolution to distinguish a prompt scattering signal from noise photons. The azimuthal and longitudinal components of the fundamental, second, and third harmonics were measured. Our measurements reasonably match theoretical results, but also show some asymmetry in the emission patterns.

In this paper we perform a statistical analysis of dark counts in superconducting nanowire single photon detectors (SNSPDs) with the end goal of creating a quantum random number generator (QRNG) using these dark counts. We confirm that dark counts are Poissonian for low bias currents and that no afterpulsing is present. However, we also show that an increase in bias current causes the dark counts to violate the independence assumption. For the non-Poissonian dark counts we identify three seemingly similar effects and confirm that: (i) a single event is at times regarded as two by the flat-threshold discriminator in the time-tagging device; (ii) a reflection in the readout circuit incites a second detection event shortly after the arrival of a first one, creating a conditionality between dark counts; (iii) a damped oscillation in the effective bias current immediately after a detection event shows itself in the inter-arrival time probability distribution. Finally, we present and evaluate a method for generating random numbers using the Poissonian dark counts as an entropy source with promising results.

Este trabalho apresenta o desenvolvimento de dispositivos semicondutores utilizando óxidos de zinco e estanho. O primeiro dispositivo semicondutor estudado está relacionado ao desenvolvimento de sensores de pH a partir do efeito de campo, enquanto que o segundo consiste na utilização de ondas acústicas de superfície para o transporte de portadores voltados para o desenvolvimento de detectores de um único fóton. Primeiramente, esses materiais foram utilizados como membranas sensíveis a íons de hidrogênio. Para isso foram fabricados os dispositivos denominados EGFETs cujo princípio de funcionamento é semelhante ao ISFET. Foram desenvolvidos filmes de SnO2 obtidos a partir da rota Pechini e pela técncia Sol-gel com o objetivo de investigar a resposta elétrica do EGFET em função da concentração de íons de H+ . Os sensores fabricados pela técnica sol-gel não apresentaram respostas satisfatórias devido à presença de poros. Por outro lado, obtivemos uma sensibilidade de 33mV/pH para o EGFET desenvolvido a partir da rota Pechini com uma membrana calcinada à 400o C. Propusemos também a utilização do ZnO como um possível candidato a sensor de pH a partir do EGFET. A melhor resposta do EGFET (uma sensibilidade de 38mV/pH) foi alcançada com a utilização de filmes de ZnO aquecidos à temperatura de 150o C. Além dos dispositivos para a detecção de íons de H+ apresentamos uma nova abordagem para a detecção de um único fóton a partir da combinação de dispositivos utilizando ondas acústicas de superfície e os transistores de um único elétron. Basicamente os protótipos consistem em uma estrutura de várias camadas otimizadas para uma eficiente absorção de fótons, uma junção p-i-n utilizada para coleta de portadores, IDT para geração da SAW e guias metálicos para controle de portadores durante o transporte acústico. Os portadores são eficientemente transportados por uma distância de 100 mm com uma perda de 12 % para a melhor configuração. Nessas condições, a eficiência do dispositivo é de 75%. / This work presents the study and development of semiconductor devices base on tin and zinc oxides. The first device is related to the development of pH sensors based on field effect, while the second device uses surface acoustic waves for the transport of carriers related to a single photon detector device. Initially, the semiconductors were used as hydrogen ions sensing membranes. For that aim extended gate field effect transistors (EGFET) were developed. Their working principle is similar to the ion sensitive field effect transistor (ISFET). Through Pechini and sol-gel SnO2 thin films were obtained. The EGFET response to H+ ions was not optimal due to the presence of pores. Using Pechini, a response of 33mV/pH was obtained for the EGFET membrane calcinated at 400o C. The use of ZnO as sensing membrane was also investigated, and the best response was a sensibility of 38mV/pH) for a film heated up to 150o C. In addition to the EGFET structure, a new approach to a single photon detection is presented. This uses the combination of surface acoustic waves with a single electron transistor. Two prototypes were developed using a multi-layered structure optimized for photon absorption. Carriers are collected using a p-i-n structure. Inter-digital-transducers are used for surface acoustinc wave generation. Metallic guides are used to control the carriers during acoustic tranport. Carriers were efficiently transported over a length of 100 mm with a loss of 12 % for the best configuration. Under this optimized conditions, the efficiency of the device is 75%.

abstract: In this dissertation research, conventional and aberration-corrected (AC) transmission electron microscopy (TEM) techniques were used to evaluate the structural and compositional properties of thin-film semiconductor compounds/alloys grown by molecular beam epitaxy for infrared photo-detection. Imaging, diffraction and spectroscopy techniques were applied to TEM specimens in cross-section geometry to extract information about extended structural defects, chemical homogeneity and interface abruptness. The materials investigated included InAs1-xBix alloys grown on GaSb (001) substrates, InAs/InAs1-xSbx type-II superlattices grown on GaSb (001) substrates, and CdTe-based thin-film structures grown on InSb (001) substrates. The InAsBi dilute-bismide epitaxial films were grown on GaSb (001) substrates at relatively low growth temperatures. The films were mostly free of extended defects, as observed in diffraction-contrast images, but the incorporation of bismuth was not homogeneous, as manifested by the lateral Bi-composition modulation and Bi-rich surface droplets. Successful Bi incorporation into the InAs matrix was confirmed using lattice expansion measurements obtained from misfit strain analysis of high-resolution TEM (HREM) images. Analysis of averaged intensity line profiles in HREM and scanning TEM (STEM) images of the Ga-free InAs/InAs1-xSbx type-II strained superlattices indicated slight variations in layer thickness across the superlattice stack. The interface abruptness was evaluated using misfit strain analysis of AC-STEM images, electron energy-loss spectroscopy and 002 dark-field imaging. The compositional profiles of antimony across the superlattices were fitted to a segregation model and revealed a strong antimony segregation probability. The CdTe/MgxCd1-xTe double-heterostructures were grown with Cd overflux in a dual-chamber molecular beam epitaxy with an ultra-high vacuum transfer loadlock. Diffraction-contrast images showed that the growth temperature had a strong impact on the structural quality of the epilayers. Very abrupt CdTe/InSb interfaces were obtained for epilayers grown at the optimum temperature of 265 °C, and high-resolution imaging using AC-STEM revealed an interfacial transition region with a width of a few monolayers and smaller lattice spacing than either CdTe or InSb. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2017

Este trabalho apresenta o desenvolvimento de dispositivos semicondutores utilizando óxidos de zinco e estanho. O primeiro dispositivo semicondutor estudado está relacionado ao desenvolvimento de sensores de pH a partir do efeito de campo, enquanto que o segundo consiste na utilização de ondas acústicas de superfície para o transporte de portadores voltados para o desenvolvimento de detectores de um único fóton. Primeiramente, esses materiais foram utilizados como membranas sensíveis a íons de hidrogênio. Para isso foram fabricados os dispositivos denominados EGFETs cujo princípio de funcionamento é semelhante ao ISFET. Foram desenvolvidos filmes de SnO2 obtidos a partir da rota Pechini e pela técncia Sol-gel com o objetivo de investigar a resposta elétrica do EGFET em função da concentração de íons de H+ . Os sensores fabricados pela técnica sol-gel não apresentaram respostas satisfatórias devido à presença de poros. Por outro lado, obtivemos uma sensibilidade de 33mV/pH para o EGFET desenvolvido a partir da rota Pechini com uma membrana calcinada à 400o C. Propusemos também a utilização do ZnO como um possível candidato a sensor de pH a partir do EGFET. A melhor resposta do EGFET (uma sensibilidade de 38mV/pH) foi alcançada com a utilização de filmes de ZnO aquecidos à temperatura de 150o C. Além dos dispositivos para a detecção de íons de H+ apresentamos uma nova abordagem para a detecção de um único fóton a partir da combinação de dispositivos utilizando ondas acústicas de superfície e os transistores de um único elétron. Basicamente os protótipos consistem em uma estrutura de várias camadas otimizadas para uma eficiente absorção de fótons, uma junção p-i-n utilizada para coleta de portadores, IDT para geração da SAW e guias metálicos para controle de portadores durante o transporte acústico. Os portadores são eficientemente transportados por uma distância de 100 mm com uma perda de 12 % para a melhor configuração. Nessas condições, a eficiência do dispositivo é de 75%. / This work presents the study and development of semiconductor devices base on tin and zinc oxides. The first device is related to the development of pH sensors based on field effect, while the second device uses surface acoustic waves for the transport of carriers related to a single photon detector device. Initially, the semiconductors were used as hydrogen ions sensing membranes. For that aim extended gate field effect transistors (EGFET) were developed. Their working principle is similar to the ion sensitive field effect transistor (ISFET). Through Pechini and sol-gel SnO2 thin films were obtained. The EGFET response to H+ ions was not optimal due to the presence of pores. Using Pechini, a response of 33mV/pH was obtained for the EGFET membrane calcinated at 400o C. The use of ZnO as sensing membrane was also investigated, and the best response was a sensibility of 38mV/pH) for a film heated up to 150o C. In addition to the EGFET structure, a new approach to a single photon detection is presented. This uses the combination of surface acoustic waves with a single electron transistor. Two prototypes were developed using a multi-layered structure optimized for photon absorption. Carriers are collected using a p-i-n structure. Inter-digital-transducers are used for surface acoustinc wave generation. Metallic guides are used to control the carriers during acoustic tranport. Carriers were efficiently transported over a length of 100 mm with a loss of 12 % for the best configuration. Under this optimized conditions, the efficiency of the device is 75%.