This thesis describes the development of a novel comprehensive Monte Carlo simulation code, ARTEMIS, for the investigation of electron-hole pair transport mechanisms in a-Se x-ray imaging detectors. ARTEMIS allows for modeling of spatiotemporal carrier transport in a-Se, combining an existing Monte Carlo simulation package, PENELOPE, for simulation of x-ray and secondary electron interactions and new routines for electron-hole pair transport with three-dimensional spatiotemporal signal output considering the effects of applied electric field. The detector Swank factor, an important imaging performance metric is calculated from simulated pulse-height spectra and shown to depend on incident x-ray energy and applied electric field. Simulation results are compared to experimental measurements and are found to agree within 2%. Clinical x-ray spectra are also used to study detector performance in terms of energy weighting and electronic noise. Simulation results show energy-weighting effects are taken into account in the ARTEMIS model, where the Swank factor and DQE have a higher dependence on the high-energy incident x rays due to increased carrier yield. Electronic noise is found to widen the pulse-height spectra and degrade the Swank factor. The effect of recombination algorithms and burst models are studied. A comparison of a first-hit algorithm and a nearest-neighbor approach shows no significant difference in the simulation output while achieving reduced simulation time. The examination of the initial generation of carriers in the burst shows that the recombination efficiency of carriers is dependent on the carrier density and electric field. Finally, the spatial resolution characteristics of a flat-panel a-Se detector are studied by using the ARTEMIS model for spatial output and image generation. The modulation transfer functions are calculated from simulated detector point response functions for monoenergetic and clinical radiation qualities.

Neste trabalho é apresentado o protótipo de um detector a gás sensível à posição em duas dimensões para aplicação com experimentos de espalhamento e difração de raios X. Partiu-se de um detector inicialmente desenvolvido para outras aplicações e mostrou-se as modificações necessárias no conceito original do dispositivo. As estratégias adotadas para determinar as adaptações essenciais foram: pesquisar na literatura sobre as características de um detector multifilar para raios X (escolha do gás, da pressão, da janela, etc.), uso de simulações, implementação das mudanças e realização de testes. Ferramentas computacionais foram usadas para estimar a resistência mecânica e a atenuação de fótons de raios X que ajudaram na determinação do material para a construção da janela de entrada. Simulações do detector foram construídas com o programa Garfield e serviram para o estudo do funcionamento do detector, além de determinar os parâmetros ótimos de operação do equipamento, como a distância entre os fios e diâmetro dos mesmos, além da diferença de potencial a ser aplicada, entre muitos outros parâmetros. Os resultados obtidos mostraram que o conceito do detector multifilar com as devidas adaptações permitem o funcionamento desse dispositivo para detecção de raios X. No entanto, dependendo da aplicação, pode ser necessário aprimorar a resolução do equipamento, a fim de ter uma melhor descrição dos dados coletados. São apontadas algumas ideias para esse aprimoramento. Apresentam-se também resultados interessantes obtidos com um detector de padrão microscópico chamado de triplo GEM. Esse dispositivo pertence ao laboratório de desenvolvimento de detectores a gás (GDD Group) do CERN e foi utilizado em um trabalho nessa instituição. Os resultados mostraram o potencial do equipamento para detecção de raios X. Os resultados e simulações apresentadas nesse trabalho confirmaram que as mudanças no conceito original do detector permitem seu uso na detecção de raios X. Além disso, foi possível obter várias indicações para uma maior otimização, que pode melhorar sua resolução e estabilidade. O conhecimento adquirido sobre o programa Garfield é fundamental nesse processo, uma vez que é possível propor mudanças e testá-las no computador. Essas melhorias podem ser empregadas em uma nova versão desse detector que será construído nos laboratórios do Instituto de Física da Universidade de São Paulo (IFUSP). Pode-se indicar ainda a possibilidade do uso de detectores GEM aplicados aos experimentos de espalhamento e difração de raios X. É necessário ressaltar que o grupo de Suaide et al. do departamento de Física Nuclear do IFUSP já trabalha com a tecnologia GEM, porém focada em outras aplicações. / This work presents the prototype of a 2D position sensitive gas detector for application in X-ray scattering and diffraction experiments. Starting from a detector initially developed for other applications and will show the required changes on the original concept of this device. The strategy used to determine the necessary adaptations were based on searching in the literature for the overall characteristics of a multi-wire X-ray detector (choice of gas, pressure, window, etc.), the use of simulations, implementation of the changes and finally operational tests. Computational tools were used to calculate the mechanical strength and attenuation of the X-ray photons that helped to determine the most appropriate material for the construction of the entrance window. Detector simulations were built with Garfield software and were used to study the overall properties of the detector, and to determine the optimum parameters for the equipment operation. Typical parameters are the distance between the wires, wire diameter, high voltage to be used, among several other parameters. The results obtained showed that the multi-wire detector concept with the implemented adaptations allowed the detection of X-rays. However, depending on the application, it may be necessary improve the resolution of the equipment, in order to have a better description of the collected data. Several ideas are suggested for this improvement. It is also presented interesting results obtained with a microscopic pattern detector called triple GEM. This device belongs to the Gas Detectors Development group (GDD group) at CERN and was used in my training at this institution. The results showed the potential of the equipment for detection of X-rays. The results and simulations presented in this work, confirmed that the changes in the concept of the original detector permitted it use on X-ray detection applications. Also, it was possible to obtain several indications for further optimization, which may improve its resolution and stability. The acquired knowledge on the software Garfield is essential on this process since it is possible to propose changes and test it in the computer. Such improvements may be use in a new version of this detector which will be built at the laboratories of the Institute of Physics (University of São Paulo - IFUSP). We also indicate the possibility of use of GEM detectors for X-ray scattering and diffraction experiments. It is necessary to emphasize that the group of Professor Alexandre Suaide and collaborators at Nuclear Physics department (IFUSP) already work with the GEM technology, but focused on other applications.

No description available.

Neste trabalho é apresentado o protótipo de um detector a gás sensível à posição em duas dimensões para aplicação com experimentos de espalhamento e difração de raios X. Partiu-se de um detector inicialmente desenvolvido para outras aplicações e mostrou-se as modificações necessárias no conceito original do dispositivo. As estratégias adotadas para determinar as adaptações essenciais foram: pesquisar na literatura sobre as características de um detector multifilar para raios X (escolha do gás, da pressão, da janela, etc.), uso de simulações, implementação das mudanças e realização de testes. Ferramentas computacionais foram usadas para estimar a resistência mecânica e a atenuação de fótons de raios X que ajudaram na determinação do material para a construção da janela de entrada. Simulações do detector foram construídas com o programa Garfield e serviram para o estudo do funcionamento do detector, além de determinar os parâmetros ótimos de operação do equipamento, como a distância entre os fios e diâmetro dos mesmos, além da diferença de potencial a ser aplicada, entre muitos outros parâmetros. Os resultados obtidos mostraram que o conceito do detector multifilar com as devidas adaptações permitem o funcionamento desse dispositivo para detecção de raios X. No entanto, dependendo da aplicação, pode ser necessário aprimorar a resolução do equipamento, a fim de ter uma melhor descrição dos dados coletados. São apontadas algumas ideias para esse aprimoramento. Apresentam-se também resultados interessantes obtidos com um detector de padrão microscópico chamado de triplo GEM. Esse dispositivo pertence ao laboratório de desenvolvimento de detectores a gás (GDD Group) do CERN e foi utilizado em um trabalho nessa instituição. Os resultados mostraram o potencial do equipamento para detecção de raios X. Os resultados e simulações apresentadas nesse trabalho confirmaram que as mudanças no conceito original do detector permitem seu uso na detecção de raios X. Além disso, foi possível obter várias indicações para uma maior otimização, que pode melhorar sua resolução e estabilidade. O conhecimento adquirido sobre o programa Garfield é fundamental nesse processo, uma vez que é possível propor mudanças e testá-las no computador. Essas melhorias podem ser empregadas em uma nova versão desse detector que será construído nos laboratórios do Instituto de Física da Universidade de São Paulo (IFUSP). Pode-se indicar ainda a possibilidade do uso de detectores GEM aplicados aos experimentos de espalhamento e difração de raios X. É necessário ressaltar que o grupo de Suaide et al. do departamento de Física Nuclear do IFUSP já trabalha com a tecnologia GEM, porém focada em outras aplicações. / This work presents the prototype of a 2D position sensitive gas detector for application in X-ray scattering and diffraction experiments. Starting from a detector initially developed for other applications and will show the required changes on the original concept of this device. The strategy used to determine the necessary adaptations were based on searching in the literature for the overall characteristics of a multi-wire X-ray detector (choice of gas, pressure, window, etc.), the use of simulations, implementation of the changes and finally operational tests. Computational tools were used to calculate the mechanical strength and attenuation of the X-ray photons that helped to determine the most appropriate material for the construction of the entrance window. Detector simulations were built with Garfield software and were used to study the overall properties of the detector, and to determine the optimum parameters for the equipment operation. Typical parameters are the distance between the wires, wire diameter, high voltage to be used, among several other parameters. The results obtained showed that the multi-wire detector concept with the implemented adaptations allowed the detection of X-rays. However, depending on the application, it may be necessary improve the resolution of the equipment, in order to have a better description of the collected data. Several ideas are suggested for this improvement. It is also presented interesting results obtained with a microscopic pattern detector called triple GEM. This device belongs to the Gas Detectors Development group (GDD group) at CERN and was used in my training at this institution. The results showed the potential of the equipment for detection of X-rays. The results and simulations presented in this work, confirmed that the changes in the concept of the original detector permitted it use on X-ray detection applications. Also, it was possible to obtain several indications for further optimization, which may improve its resolution and stability. The acquired knowledge on the software Garfield is essential on this process since it is possible to propose changes and test it in the computer. Such improvements may be use in a new version of this detector which will be built at the laboratories of the Institute of Physics (University of São Paulo - IFUSP). We also indicate the possibility of use of GEM detectors for X-ray scattering and diffraction experiments. It is necessary to emphasize that the group of Professor Alexandre Suaide and collaborators at Nuclear Physics department (IFUSP) already work with the GEM technology, but focused on other applications.

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.

Abstract Amorphous Selenium (a-Se) was first commercialized for use as a photoconductor in xerography during the middle of the twentieth century. Since then the hole transport properties of a-Se have been studied extensively, however the study of electron transport remains relatively limited. Flat panel digital X-ray detectors using a-Se as a photoconductor have been developed and are being used in mammographic screening. The charge transport properties of the photoconductor layer will in part determine the performance of the flat panel detector. X-ray absorption causes electron-hole pair generation in the bulk of the photoconductor, requiring both electrons and holes to drift across the sample and be collected. If these carriers are lost in the many localized trapping states as they cross the sample, they will not contribute to the image signal resulting in unnecessary radiation exposure to the patient. Eleven a-Se samples were deposited at the University of Saskatchewan varying in thickness from 13 μm to 501 μm. Pure a-Se was chosen to ensure uniformity across the thickness of the samples, that is, to ensure the composition of the film did not change across the thickness. Time of flight transient photoconductivity experiments (TOF) and interrupted field time of flight (IFTOF) measurements were performed to measure the electron drift mobility and lifetime respectively. The product of electron drift mobility μ and lifetime τ, hence the carrier range (μτ) at a given applied electric field. The electron range is an important parameter as this places limits on the practical thickness of the photoconducting layer in a detector. This study also includes an investigation into the effect of the definition of transit time on the calculated drift mobility and analysis of the dispersive transport properties of a-Se. It was observed that as sample thickness (L) increased, electron drift mobility (μ) decreased. In addition electron lifetime (τ) decreased dramatically in samples thinner than 50 μm. Electron range (μτ) was 2.26 × 〖10〗^(-6) cm^2/V in the 147μm sample and 5.46 × 〖10〗^(-8) cm^2/V in the 13 μm sample, a difference of almost two orders of magnitude. The comparison of the half current method and inflection point methods to calculate the transit time of the same TOF curve, shows that the calculated mobility can vary by as much as 24%. This illustrates clearly that it is important to use the same point on the TOF curve to define the transit time. Charge packet dispersion (spread) in the time domain in pure a-Se samples was proportional to L^m where L is the photoconductor thickness and m ~ 1.3, measured at both 1 V/μm and 4 V/μm.

Pesquisadores em todo o mundo buscam métodos alternativos que minimizem o tempo de deposição de filmes finos semicondutores cotados como promissores candidatos em aplicações médicas como detectores de raios-X em radiografias digitais. O iodeto de chumbo (PbI2) é considerado, entre outros, como um bom candidato para a fabricação de detectores usados à temperatura ambiente. Outros pesquisadores fabricaram protótipos de detectores usando esse material. Seus experimentos mostraram alta resolução e sensibilidade para imagens em tempo real, mostrando que o material possui potencialidade para aplicações médicas futuramente. Não obstante, uma das desvantagens de seus métodos é o longo tempo necessário para a deposição na fabricação de filmes finos. Este trabalho apresenta uma nova metodologia usada para a deposição de filmes finos de iodeto de chumbo (PbI2). O método alternativo de crescimento dos filmes é chamado de spray pyrolysis. A técnica possui uma vantagem intrínseca pelo fato de a deposição ser facilmente expandida para grandes áreas de substrato que é desejado nas linhas de produção industrial. O pó de iodeto de chumbo foi dissolvido em água deionizada a 100ºC (água em ebulição) onde a solubilidade é maior que à temperatura ambiente. Após a dissolução do pó, a solução foi resfriada até a temperatura ambiente e filtrada para a remoção do excesso de cristais formados. Os filmes foram depositados a partir de solução aquosa sobre substrato de vidro em diferentes temperaturas (de 150 a 270ºC). O tempo total de deposição foi de 2,5 horas levando a uma espessura de . Em adição foram investigadas as propriedades estruturais (Difração de raios-X e espalhamento Raman), eletrônicas (condutividade elétrica no escuro em função da temperatura) e da superfície (por AFM) obtidas com os filmes produzidos. Com o intuito de aumentar o tamanho dos grãos cristalinos após a deposição dos filmes, as amostras originais foram submetidas a tratamento térmico a 350ºC durante 3 horas em atmosfera ambiente e posteriormente em atmosfera controlada (N2). No primeiro caso foi observada a influência do oxigênio com dopante da amostra. Foram analisadas as dimensões dos grãos cristalinos (relativo ao pico principal – 001) para diferentes temperaturas de deposição e de tratamento térmico, bem como a energia de ativação no transporte elétrico. Obteve-se um valor de energia de ativação de aproximadamente 0,50 eV para filmes depositados a 200ºC. Para outras temperaturas de deposição entre 150 e 250ºC foi obtido um mínimo e máximo de energia de ativação de 0,45 e 0,66 eV, respectivamente. Em resumo, as propriedades estruturais e eletrônicas são discutidas e relacionadas com o método de deposição e tratamento térmico. Acreditamos que filmes finos com interessantes propriedades estruturais e eletrônicas podem ser produzidos por spray pyrolysis com baixo tempo de deposição. / Researchers in the whole world search alternative methods that minimize the time of deposition of thin films of promising semiconductor candidates for medical applications, such as X-rays detectors for digital radiography. Lead iodide (PbI2) has been among those as a good candidate for the fabrication of room temperature detectors. Other authors have fabricated prototype detectors using this material. Their experiments show high resolution and sensitivity for real time imaging, thus showing the material potentiality for medical applications in the future. Nevertheless, one of the drawbacks of their methods is the long deposition time needed for the fabrication of the thin films. In this work we present a new experimental methodology used for the deposition of thin films of lead iodide (PbI2). The alternative growth method is called spray pyrolysis. Note that an intrinsic advantage of the technique is the fact that it can be easily expanded for large area substrates as desired by the industrial fabrication line. Lead iodide powder was dissolved in deionized water at 100ºC (boiling water) where its solubility is higher than at room temperature. After the dissolution of the powder, the solution is cooled down to ambient temperature and filtered for the removal of the excess of formed crystals. The films were deposited from aqueous solutions on glass substrates sitting at different temperatures (from 150 to 270ºC). The total deposition time is about 2.5 hours leading to a film thickness of . In addition we also investigate the structural (X-ray diffraction and Raman scattering), electronic (dark conductivity as a function of temperature) and atomic force microscopy (AFM) properties of the obtained films. In order to induce crystalline grain growth after the deposition of the films, the original samples were also submitted to thermal treatment at 350ºC during 3 hours either in ambient or under controlled atmosphere (N2). The influence of oxygen doping was only observed in the first case. We analyze the variation of the size of the crystals (relative to the main peak - 001) and the activation energies for electric transport. The activation energy for films deposited at 200ºC is about 0.50 eV. For other deposition temperatures, varying from 150 to 250ºC, it was experimentally measured a minimum and maximum value of activation energy of 0.45 and 0.66 eV, respectively. In summary, the electronic and structural properties are correlated and discussed based on the deposition method, and thermal treatments. It is the present authors belief that thin films with interesting structural and electronic properties can be produced by spray pyrolysis with short deposition time.

Pesquisadores em todo o mundo buscam métodos alternativos que minimizem o tempo de deposição de filmes finos semicondutores cotados como promissores candidatos em aplicações médicas como detectores de raios-X em radiografias digitais. O iodeto de chumbo (PbI2) é considerado, entre outros, como um bom candidato para a fabricação de detectores usados à temperatura ambiente. Outros pesquisadores fabricaram protótipos de detectores usando esse material. Seus experimentos mostraram alta resolução e sensibilidade para imagens em tempo real, mostrando que o material possui potencialidade para aplicações médicas futuramente. Não obstante, uma das desvantagens de seus métodos é o longo tempo necessário para a deposição na fabricação de filmes finos. Este trabalho apresenta uma nova metodologia usada para a deposição de filmes finos de iodeto de chumbo (PbI2). O método alternativo de crescimento dos filmes é chamado de spray pyrolysis. A técnica possui uma vantagem intrínseca pelo fato de a deposição ser facilmente expandida para grandes áreas de substrato que é desejado nas linhas de produção industrial. O pó de iodeto de chumbo foi dissolvido em água deionizada a 100ºC (água em ebulição) onde a solubilidade é maior que à temperatura ambiente. Após a dissolução do pó, a solução foi resfriada até a temperatura ambiente e filtrada para a remoção do excesso de cristais formados. Os filmes foram depositados a partir de solução aquosa sobre substrato de vidro em diferentes temperaturas (de 150 a 270ºC). O tempo total de deposição foi de 2,5 horas levando a uma espessura de . Em adição foram investigadas as propriedades estruturais (Difração de raios-X e espalhamento Raman), eletrônicas (condutividade elétrica no escuro em função da temperatura) e da superfície (por AFM) obtidas com os filmes produzidos. Com o intuito de aumentar o tamanho dos grãos cristalinos após a deposição dos filmes, as amostras originais foram submetidas a tratamento térmico a 350ºC durante 3 horas em atmosfera ambiente e posteriormente em atmosfera controlada (N2). No primeiro caso foi observada a influência do oxigênio com dopante da amostra. Foram analisadas as dimensões dos grãos cristalinos (relativo ao pico principal – 001) para diferentes temperaturas de deposição e de tratamento térmico, bem como a energia de ativação no transporte elétrico. Obteve-se um valor de energia de ativação de aproximadamente 0,50 eV para filmes depositados a 200ºC. Para outras temperaturas de deposição entre 150 e 250ºC foi obtido um mínimo e máximo de energia de ativação de 0,45 e 0,66 eV, respectivamente. Em resumo, as propriedades estruturais e eletrônicas são discutidas e relacionadas com o método de deposição e tratamento térmico. Acreditamos que filmes finos com interessantes propriedades estruturais e eletrônicas podem ser produzidos por spray pyrolysis com baixo tempo de deposição. / Researchers in the whole world search alternative methods that minimize the time of deposition of thin films of promising semiconductor candidates for medical applications, such as X-rays detectors for digital radiography. Lead iodide (PbI2) has been among those as a good candidate for the fabrication of room temperature detectors. Other authors have fabricated prototype detectors using this material. Their experiments show high resolution and sensitivity for real time imaging, thus showing the material potentiality for medical applications in the future. Nevertheless, one of the drawbacks of their methods is the long deposition time needed for the fabrication of the thin films. In this work we present a new experimental methodology used for the deposition of thin films of lead iodide (PbI2). The alternative growth method is called spray pyrolysis. Note that an intrinsic advantage of the technique is the fact that it can be easily expanded for large area substrates as desired by the industrial fabrication line. Lead iodide powder was dissolved in deionized water at 100ºC (boiling water) where its solubility is higher than at room temperature. After the dissolution of the powder, the solution is cooled down to ambient temperature and filtered for the removal of the excess of formed crystals. The films were deposited from aqueous solutions on glass substrates sitting at different temperatures (from 150 to 270ºC). The total deposition time is about 2.5 hours leading to a film thickness of . In addition we also investigate the structural (X-ray diffraction and Raman scattering), electronic (dark conductivity as a function of temperature) and atomic force microscopy (AFM) properties of the obtained films. In order to induce crystalline grain growth after the deposition of the films, the original samples were also submitted to thermal treatment at 350ºC during 3 hours either in ambient or under controlled atmosphere (N2). The influence of oxygen doping was only observed in the first case. We analyze the variation of the size of the crystals (relative to the main peak - 001) and the activation energies for electric transport. The activation energy for films deposited at 200ºC is about 0.50 eV. For other deposition temperatures, varying from 150 to 250ºC, it was experimentally measured a minimum and maximum value of activation energy of 0.45 and 0.66 eV, respectively. In summary, the electronic and structural properties are correlated and discussed based on the deposition method, and thermal treatments. It is the present authors belief that thin films with interesting structural and electronic properties can be produced by spray pyrolysis with short deposition time.

Two-dimensional transition metal dichalcogenides (TMDCs) aroused significant interest in the last years as semiconductor materials for application in the field of electronics, due to their tunable bandgap, good carrier mobility, and strong light absorption. Among TMDCs, two-dimensional molybdenum disulfide (2D-MoS2) has been the most investigated for electronic and optoelectronic applications, like transistors and photodetectors. 2D-MoS2 can particularly benefit from the excellent light matter interaction properties in the UV-VIS spectrum combined with good charge carrier transport properties. The literature reports photodetectors based on 2D-MoS2 fabricated with different techniques, including exfoliation, chemical vapor deposition (CVD) and wet chemical synthesis. However, it is still challenging to scale the proposed devices to the industrial level, due to the lack of a versatile fabrication process that ensures both reproducibility and scalability. A possible solution to this could rise from wet chemical synthesis. In the first part of this work, I discuss the development and optimization of a fabrication method for MoS2 thin films based on a sol-gel process which allows for scalable productions. This route allowed the fabrication of large area (~cm2) MoS2 thin films of 200 nm thickness on technological relevant substrates (i.e., glass, gold, silicon). The films displayed good uniformity, although the crystallinity was affected by residual impurities. The films produced with this technique were employed for the fabrication of photodetectors, displaying responsivity of few mA/W in the NUV-VIS-NIR spectrum. However, the performance of the device was affected by a still limited quality of the MoS2 films obtained with the current method that require further optimization. Further studies will overcome the current limitations and solutions to be investigated in future works are proposed. The second part of this work focuses on expanding the detection capability of 2D-MoS2 (currently limited to the UV-VIS-NIR spectrum), by exploring for the first time X-rays sensing, taking advantage of the X-ray cross section of MoS2 associated with the high atomic number Z of Mo. A detector based on an exfoliated MoS2 monolayer (1L-MoS2) was fabricated and characterized for the purpose. The detector showed direct detection of ~10^2 keV X-rays down to dose rates of 0.08 mGy/s, with X-ray sensitivity is in the range 10^8-10^9 µC ⋅Gy-1·cm-3, outperforming most of the reported organic and inorganic materials. A strategy to improve the device response was also studied by adding a scintillator film, which resulted in a three-fold increase of the signal. These results suggest to consider 2D-MoS2 for in-vivo dosimetry applications.

Ces travaux de doctorat proposent d’apporter une contribution à l’identification et à la compréhension des phénomènes limitant les performances de détecteurs de rayon X à base de CdTe:Cl développés pour des applications en radiographie. En effet, des inhomogénéités spatiales non-stables dans le temps sont observées dans la réponse de ces capteurs. Les défauts des cristaux utilisés pour la détection ont été caractérisés. Notamment, les dislocations révélées par attaque chimique et par topographie X présentent des arrangements en mur à la surface des échantillons, ces défauts sont majoritairement traversant dans toute l’épaisseur du cristal. Il a ensuite été montré que ces murs de dislocations sont responsables des inhomogénéités de photo-courant sous irradiation par des rayons X et de courant de fuite d’un détecteur à base de CdTe:Cl. De plus, les niveaux pièges dans le gap du CdTe ont été investigués par des méthodes de spectroscopie optique à basse température : les images de cathodoluminescence mettent en évidence le caractère non-radiatif des murs de dislocations, mais ne montrent pas l’apparition de la luminescence Y au niveau de ces défauts, normalement attribuée aux dislocations dans la littérature. Enfin, l’influence des murs de dislocations sur les propriétés de transport des porteurs de charge a été étudiée par la méthode « Ion Beam Induced Current » (IBIC) montrant qu’ils entraînent une diminution de la valeur du produit mobilité-temps de vie des électrons et des trous / In the present Ph.D. thesis, we investigate microstructural defects in a chlorine-doped cadmium telluride crystal (CdTe:Cl), to understand the relationship between defects and performance of CdTe-based radiation detectors. Characterization tools, such as diffraction topography and chemical etching, are used for bulk and surface investigations of the distribution of dislocations. Dislocations are arranged into walls. Most of them appear to cross the whole thickness of the sample. Very good correlation is observed between areas with variations of dark-current and photo-current, and positions of the dislocation walls revealed at the surface of the sample. Then spectroscopic analysis of these defects was performed at low temperatures. It highlighted that dislocation walls induce non-radiative recombination, but it didn’t show any Y luminescence usually attributed to dislocations in the literature. Ion Beam Induced Current (IBIC) measurements were used to evaluate the influence of dislocation walls on charge carrier transport properties. This experiment shows that they reduce the mobility-Iifetime product of the charge carriers. A very clear correlation was, in fact, established between the distribution of the dislocation network and the linear defects revealed by their lower CIE on the device