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1
Valaparla, Sunil K. « Experimental study of the response of semiconductor detectors for EDXRF analysis ». To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
Texte intégral
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Barnett, Anna Megan. « Wide band gap compound semiconductor detectors for x-ray spectroscopy in harsh environments ». Thesis, University of Leicester, 2012. http://hdl.handle.net/2381/10375.
Texte intégralRésumé :
Novel photon counting Alo.8Gao.2As, GaAs and SiC X-ray photodiodes were investigated through experiments and Monte Carlo computer simulations for their suitability as spectroscopic soft (:S 25 keY) X-ray detectors in high temperature (up to 90 QC) environments. Photon counting Alo.8Gao.2As and GaAs non-avalanche p+-i-n+ mesa X-ray photodiodes were shown to operate at temperatures as high as 90 QC. The temperature dependences of their spectral resolutions (FWHM at 5.9 keY) are reported. Analyses of the noise sources contributing to the devices' measured performances are presented which suggest that efforts to improve the spectral resolutions would be well targeted at reducing the noise contributions from the packaging of the detectors. For the GaAs diodes, the X-ray characterisation of the devices was extended to higher energies (25 keY). Internal detector X-ray fluorescence was demonstrated and Monte Carlo computer simulations were compared with the experimental results. Prior to the research presented in this thesis, the only Alo.8Gao.2As photon counting X-ray avalanche photodiodes reported in the literature (Lees et al., 2008, Nucl. Instr. and Meth. A, Vol. 594, pp. 202-205) had shown anomalies in the obtained spectra. Through new experimental measurements and computer simulations, the anomaly is explained. A new method was developed which uses the phenomenon to extract measurements of the electron and hole ionisation coefficients of Alo.8Gao.2As at a typical operating field and the first report of their temperature dependence is made. Measurements characterising the X-ray spectroscopic performance of Semi-Transparent SiC Schottky Diodes over an energy range ~6 keY to 25 keY at temperatures up to 80 QC are presented and discussed, along with relative efficiency measurements and data showing the temperature dependence of the leakage current in such devices. The research presented in this thesis shows that Alo.8Gao.2As, GaAs and SiC X-ray detectors are promising devices for high temperature soft X-ray spectroscopy.
3
MAGALHAES, RODRIGO R. de. « Espectrometria de raios-x com diodos de Si ». reponame:Repositório Institucional do IPEN, 2000. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10807.
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
FAPESP:97/12485-4
4
Menezes, Tiago. « Room temperature CdZnTe X- and gamma-ray detectors for nuclear physics applications ». Thesis, University of Surrey, 2000. http://epubs.surrey.ac.uk/842705/.
Texte intégralRésumé :
Gamma-ray spectroscopy is undoubtedly the most effective tool for understanding the structure of the nucleus. In common with many other problems however, there is more information available that can be readily measured by standard experimental facilities. Therefore, this thesis investigates the potential for the use of a new detector material, CdZnTe, in nuclear physics applications. To evaluate the requirements of detection systems for nuclear physics applications, a y-ray spectroscopy experiment was performed to investigate neutron alignments in 100Mo, 104Ru and 108Pd using deep-inelastic reactions. This showed that a detector capable of detecting low energy (< 100 keV) X- rays without compromising y-ray detection efficiency could have significant benefit. A room temperature CdZnTe semiconductor detector could reasonably form part of a standard escape suppressed spectrometer. However, there is a substantially higher leakage current associated with room temperature semiconductor devices than standard cryogenically cooled semiconductor detectors. CdZnTe suffers from significant charge trapping, and therefore the rise time of the radiation induced pulses forms an important part of the signal analysis from such detectors. These two problems have implications on the design of preamplifier systems for CdZnTe detectors. For this reason, this thesis describes the design of optimised electronic systems for use with room-temperature operated CdZnTe detectors. Here, the focus is on the preamplifier design, and on practical ways of analysing noise performance of the preamplifier. A new preamplifier configuration with digital output has been developed, and a detailed signal-to-noise analysis performed. Such a circuit facilitates simultaneous measurement of both energy and pulse shape information.
5
Meng, Xiao. « InGaAs/InAlAs single photon avalanche diodes at 1550 nm and X-ray detectors using III-V semiconductor materials ». Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/11405/.
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Знаменщиков, Ярослав Володимирович, Ярослав Владимирович Знаменщиков, Yaroslav Volodymyrovych Znamenshchykov, Володимир Володимирович Косяк, Владимир Владимирович Косяк, Volodymyr Volodymyrovych Kosiak, Анатолій Сергійович Опанасюк, Анатолий Сергеевич Опанасюк, Anatolii Serhiiovych Opanasiuk et P. M. Fochuk. « Effect of Laser Annealing on the Properties of the Surface of Polycrystalline CdZnTe Thick Film ». Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42798.
Texte intégralRésumé :
In this work effect of laser annealing on properties of surface of CdxZn1-xTe (CZT) films was studied. CZT layers were deposited by co-evaporation of CdTe and ZnTe using close-spaced vacuum sublimation (CSVS) method. Structural properties and chemical composition of films were studied by X-ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS). The annealing of the sample was carried out with the
help of micro-Raman infrared laser of 785 nm wavelength at maximal 100x magnification. It was established that laser annealing of the surface substantially causes redistribution of Zn atoms. More detailed study of the sample by the scanning of surface with the micro-Raman method allows to determine trend in this process and to detect Te-rich zones. Improvement of the crystal quality near annealed area of the thick
film was achieved.
7
LE, DONNE ALESSIA. « Defects in silicon carbide : effect on electrical and optical properties ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2004. http://hdl.handle.net/10281/132184.
Texte intégralRésumé :
Nowadays semiconductor detectors are widely used for ionizing radiation spectrometry and imaging in many fields such as fundamental scientific research, material science, medical applications, security systems, archeometry and many industrial applications. The highest performance required to the detectors in terms of energy and spatial resolution, room temperature operation and radiation hardness have brought to an intense international research activity on several compound semiconductors in order to overcome the limits imposed by the conventional materials (Si and Ge).
The main problems arising on using compound semiconductors (GaAs, CdTe, CdZnTe, InP…) for radiation detectors are related to the crystal impurities and defects, which are responsible of charge thermal generation and trapping, and to the junction barrier height, which determines a component of the junction reverse current, which limit the signal to noise ratio and the maximum operating temperature.
In the last years, silicon carbide (SiC) has been investigated as material to fabricate radiation detectors, particularly due to its intrinsic properties, which make it potentially superior to the most common semiconductor materials. This is, in particular, related to its wide band gap, resulting in low leakage current, even at high operating temperature, and to high displacement energy, making SiC detectors less susceptible to bulk radiation damage effects. Moreover, it has recently been demonstrated that a metal-SiC junction shows extremely low current densities, even at room temperature, and this feature is very favourable for the realization of low-noise X-ray semiconductor detectors.
In this thesis work the results of a research activity on low-noise X-ray detectors based on SiC will be showed. The aim of this study was both to deeply understand the structural, electrical and optical properties of SiC materials available for the device realisation and, at the same time, to investigate the effects of irradiation on SiC properties. A fundamental understanding of defect creation, accumulation, and recovery in irradiated SiC is in fact needed to advance the device fabrication and evaluate their performance in high-radiation environments.
The first step of this work has been a wide-ranging characterization of as-grown SiC substrates and epilayers. Later on, the detectors have been irradiated with electrons and neutrons in order to preliminarily test their radiation hardness and the resulting damage has mainly been studied by Photoluminescence (PL) and the Deep Level Transient Spectroscopies (DLTS) and by monitoring the minority carrier diffusion length of the samples. To this purpose two different methods for the determination of the minority carriers diffusion length have been developed, the former based on a spectral response technique, the latter based on OBIC (Optical Beam Induced Current) mapping.
8
Spisni, Giacomo. « Radiation-sensitive OXide semiconductor Field Effect Transistor (ROXFET) : a novel thin-film device for real-time and remote ionizing radiation detection ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24394/.
Texte intégralRésumé :
Nowadays, ionizing radiation detectors find application in a wide range of contexts, spanning from industry to healthcare and security. In this background, the next generation of ionizing radiation sensors require devices that are accurate, light-weight, relatively inexpensive and capable to be read-out in real-time and remotely. In recent years, research groups at the University of Bologna and the NOVA University of Lisbon (Portugal) have developed Radiation-sensitive OXide-semiconductor Field-Effect Transistors (ROXFET) to be employed as fast, real-time x-ray dosimetry detection systems. The ROXFET operation relies on the principle that, upon exposure to radiation, excitons are generated in the dielectric and separated into hole and electron charge carriers. While electrons are able to diffuse out of the dielectric layer, hole charges get trapped and contribute to the field-effect in the semiconductor channel. Macroscopically, such contribution is observable as a shift in transistor threshold voltage toward negative values, which turns out to be proportional to the absorbed radiation dose. In laboratory tests, ROXFET devices proved to be sensitive in a wide energy range and capable of providing reliable information about their radiation exposure history. Furthermore, the design of ROXFET can be integrated on a flexible substrate and read in real-time as a passive radiofrequency tag. Aim of this thesis work was to contribute to the development of the ROXFET technology. To this end, I carried out multiple characterization tests on recently fabricated samples, revealing how they outperformed previously observed radiation sensitivities. Later on, I worked in a clean-room facility to fabricate new ROXFET experimental samples by leveraging the knowledge acquired from previous observations.
9
MOGUILINE, ERIC. « Evaluation et developpement de detecteurs semiconducteurs pour la spectroscopie d'absorption x ». Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10240.
Texte intégralRésumé :
Divers types de detecteurs en silicium ont ete developpes pour la spectroscopie d'absorption x: des photodiodes sont utilisees comme moniteurs d'intensite et de position ; des detecteurs a champ de derive ont ete concus pour l'analyse de la fluorescence x en dispersion d'energie. La premiere partie du memoire rappelle le principe de la spectroscopie d'absorption x et les aspects experimentaux essentiels sont decrits. Les problemes specifiques aux divers modes de detection sont analyses, ainsi que leur incidence sur les caracteristiques des detecteurs. La deuxieme partie concerne les photodiodes utilisees en mode d'integration de courant. Diodes et electrometres doivent posseder d'excellentes caracteristiques en termes de linearite, gamme dynamique et rapport signal sur bruit. Les faisceaux de rayons x sont modules pour permettre une detection synchrone digitale. Ce dispositif donne de remarquables performances illustrees par des spectres experimentaux. Une photodiode a division de courant permet aussi de mesurer des deplacements de faisceau avec une precision micrometrique. La troisieme partie est consacree a de nouveaux types de detecteurs a champ de derive. Avec une faible capacite electrique de l'electrode de lecture pour une grande surface active, ces detecteurs possedent une tres bonne resolution en energie pour un tres fort taux de comptage. Un nouveau concept de detecteur multivoie a ete etudie et mis en uvre avec des preamplificateurs a tres bas bruit. Un cryostat a ete developpe pour le montage de 4 detecteurs totalisant 32 voies. Un autre projet plus ambitieux vise l'integration d'un transistor jfet directement dans le substrat du detecteur. La resolution en energie mesuree devient alors excellente, meme a temperature ambiante et avec de courtes constantes de filtrage. Les premiers spectres exafs ont ete enregistres avec ce type de detecteur
10
PEREIRA, LILIAN N. « Uso de diodos epitaxiais de Si em dosimetria de fótons ». reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10581.
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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
11
Raspanti, Fabio. « Organic small molecules semiconductors as direct X-ray detectors ». Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15451/.
Texte intégralRésumé :
Organic small molecules semiconductors are promising in the field of direct ionizing radiation detection.
Unlike their inorganic counterpart, these molecules are easy to work with, since they are flexible, soluble and can be deposited on electronic devices with very simple processes, such as drop-casting and spin-casting. Moreover, these materials have good detection properties and very low working voltage.
To this day, organic semiconductors have mainly been used in indirect radiation detection, employed both in scintillator and as photodetectors. However, direct detection of ionizing radiation is a far more effective method, since it is performed within a single material and a single conversion, directly from photons to electrical signal; furthermore, it provides a higher signal-to-noise ratio and a faster response time.
In this experimental work, I fabricated four direct detectors based on transistors; two different organic solutions were drop-casted onto the transistors, creating a conduction channel between source and drain electrodes.
Both these solutions had chlorobenzene as a solvent, with DiF-TES-ADT and DiF-TEG-ADT as solutes, respectively, in a 0.5% concentration.
The purpose of this thesis is dual. Firstly, I want to study how the detectors’ sensitivity is influenced by semiconductor molecules with different Z-number; secondly, I want to test a new drop-casting method (SAC method) and compare it to results previously obtained with traditional deposition methods.
The results are very promising, with very high values of sensitivity obtained with low voltages.
12
SANTOS, ROBINSON A. dos. « Estudo da influência de impurezas e da qualidade das superfícies em cristais de brometo de tálio para aplicação como um detector de radiação ». reponame:Repositório Institucional do IPEN, 2016. http://repositorio.ipen.br:8080/xmlui/handle/123456789/26818.
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Neste trabalho, cristais de TlBr foram crescidos e purificados pelo método de Bridgman Repetido, a partir de sais comerciais de TlBr, e caracterizados para serem usados como detectores de radiação à temperatura ambiente. Para avaliar a eficiência de purificação, estudos da diminuição da concentração de impurezas foram feitos após cada crescimento, analisando as impurezas traço por Espectrometria de Massas com Plasma (ICP-MS). Um decréscimo significativo da concentração de impurezas em função do número de purificações foi observado. Os cristais crescidos apresentaram boa qualidade cristalina de acordo com os resultados de análise por Difração de Raios X (DRX), boa qualidade morfológica e estequiometria adequada de acordo com os resultados de análise por MEV(SE) e MEV(EDS). Um modelo matemático definido por equações diferenciais foi desenvolvido para avaliar as concentrações de impurezas no cristal de TlBr e suas segregações em função do número de crescimentos pelo método de Bridgman. Este modelo pode ser usado para calcular o coeficiente de migração das impurezas e mostrou ser útil para prever o número necessário de repetições de crescimento Bridgman para atingir nível de pureza adequado para assegurar a qualidade do cristal como detector de radiação. Os coeficientes se segregação obtidos são parâmetros importantes para análise microestrutural e análise de transporte de cargas nos cristais detectores. Para avaliar os cristais a serem usados como detectores de radiação, medidas de suas resistividades e resposta à incidência de radiação gama das fontes de 241Am (59,5keV) e 133Ba (81 keV) foram realizadas. Essa resposta foi dependente da pureza do cristal. Os detectores apresentaram um avanço significativo na eficiência de coleta de cargas em função da pureza.
Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
13
SANTOS, LUCAS R. dos. « Desenvolvimento de um protocolo de calibração utilizando espectrometria e simulação matemática, em feixes padrões de raios x ». reponame:Repositório Institucional do IPEN, 2017. http://repositorio.ipen.br:8080/xmlui/handle/123456789/28026.
Texte intégralRésumé :
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A calibração, por definição, é o processo pelo qual se estabelece uma relação entre valores de medição de um padrão, com as suas respectivas incertezas, e as indicações com as incertezas associadas do instrumento de medição a ser calibrado. Um protocolo de calibração descreve a metodologia a ser aplicada em um processo de calibração. O método escolhido para a obtenção deste protocolo foi o da espectrometria de feixe de raios X associada à simulação pelo método de Monte Carlo, fundamentado no fato de que ambos são considerados métodos absolutos na determinação de parâmetros de feixes de radiação. Neste trabalho foi utilizado o método de Monte Carlo utilizado para obter a função resposta do detector utilizada para a correção dos espectros obtidos do feixe primário de radiação X; deste modo foram calculadas as taxas de kerma destes feixes e comparadas aos valores obtidos com as câmaras de ionização padrão secundário do Laboratório de Calibração de Instrumentos do IPEN (LCI/IPEN). Foram obtidos os coeficientes de calibração para o sistema padrão com diferenças em relação ao fornecido pelo laboratório primário entre 1,3% e 15,3%. Os resultados obtidos indicaram a viabilidade do estabelecimento deste protocolo de calibração utilizando a espectrometria como padrão de referência, com incertezas relativas de 0,62% para k=1. As incertezas associadas ao método proposto foram satisfatórias, para um laboratório padrão secundário e comparáveis a um laboratório primário.
Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
14
Zanazzi, Enrico. « Characterization of X-ray detectors based on organic semiconducting single crystals ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8750/.
Texte intégralRésumé :
Negli anni recenti, lo sviluppo dell’elettronica organica ha condotto all’impiego di materiali organici alla base di numerosi dispositivi elettronici, quali i diodi ad emissione di luce, i transistor ad effetto di campo, le celle solari e i rivelatori di radiazione. Riguardo quest’ultimi, gli studi riportati in letteratura si riferiscono per la maggiore a dispositivi basati su materiali organici a film sottile, che tuttavia presentano problemi relativi ad instabilità e degradazione. Come verrà illustrato, l’impiego di singoli cristalli organici come materiali alla base di questi dispositivi permette il superamento delle principali limitazioni che caratterizzano i rivelatori basati su film sottili. In questa attività sperimentale, dispositivi basati su cristalli organici semiconduttori verranno caratterizzati in base alle principali figure di merito dei rivelatori. Tra i campioni testati, alcuni dispositivi basati su singoli cristalli di 6,13-bis (triisopropylsilylethynyl)-pentacene (TIPS-Pentacene) e 5,6,11,12-tetraphenyltetracene (Rubrene) hanno mostrato interessanti proprietà e sono stati quindi maggiormente studiati.
15
Kazemi, Shada. « Design, development and fabrication of a new generation semiconductor X-ray detector ». Thesis, University of Surrey, 2010. http://epubs.surrey.ac.uk/843693/.
Texte intégralRésumé :
X-ray detectors are used in a number of areas, namely in astronomy, microscopy, medical imaging diagnostic, biological science and material analysis. Demand is rising significantly within the industry for X-ray detectors that do not require a cooling system, e.g. pin-diode detectors. The elimination of the cooling system will facilitate the design of portable detectors. Development of this technology opens opportunities for the design of new instruments and the manufacture of more specialist detectors for customised applications. The rapid progress of the semiconductor industry has enabled the construction of more sophisticated electronic devices. This progress has also resulted in the creation of simulation tools, which enable researchers to simulate the processing of their devices. This method is more time and cost efficient as different models can be tested before actually investing in device processing in a laboratory. For this project we have used Silvaco simulation tools and packages to design nine different pin-diode X-ray detectors and evaluated their electrical performance before manufacturing them. Microfabrication technology has also been employed to make the pin-diode X-ray detectors that are capable of simultaneously detecting low X-ray energies (< 10 keV) and measure the radiation energies with high sensitivity, speed and resolution. The X- ray detectors have been manufactured using the University of Surrey's cleanroom and laboratories. This project is run as a Knowledge Transfer Partnership scheme in partnership with e2V Scientific Instruments (e2Vsi). To improve efficiency and productivity in industry, recent years have seen increased collaboration between industry and academia. New technologies have been commercialised with varying degrees of success and new applications have emerged, also benefiting academic research. e2Vsi is a manufacturing company specialising in the design, development and production of high resolution semiconductor X-ray detectors and the project objectives are therefore closely aligned with industry's needs.
16
Mariotti, Francesco. « Characterization of organic thin film devices for direct X-ray photoconversion ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/17048/.
Texte intégralRésumé :
The main purpose of this thesis is to present the fundamental characteristics of organic thin film devices for direct X-ray photoconversion. In the first part of this study will be presented the theoretical background of X-rays, X-rays detection and the theory organic devices.
In the second part will be considered in details the process of fabrication and characterization of organic devices projected for X-rays detection. The subjects of this thesis are some samples realized at the laboratories of the Department of Physics and Astronomy of Bologna: their fabrication and their
electrical and X-rays characterization will be analised in this work. These samples have been realized on 5 different ”substrates” in order to study their effect on the behaviour of the device. In the third and last part will be presented the characterization of a TIPGe device realized at the labora-
tories of the Department of Physics and Astronomy of Bologna, and tested at Skan-X Radiology Devices S.p.A. The collaboration with this company offered the
possibility to test the device with a complete different sets of parameters, in energy and dose range typical of dental medical applications. Moreover it was a constructive collaboration under the aspect of further developments of the device: physicists and experts from Skan-X Radiology Devices S.p.A. and from SkanRay S.p.A. defined the key points that organic
thin film devices for direct X-ray photoconversion should have to work as a X-rays detectors for radiographic imaging.
The encouraging results placed the bases for further analysis such as testing the device with other X-ray machine or/and trying to better understand the effect of the substrates on the behaviour of the device. In addition they represent the starting point for the beginning of the process of scaling of the device in order to move towards the fabrication of a prototype of X-rays detector for radiographic imaging
17
Pan, Lei. « Development of perovskite for X-ray detection and gamma-ray spectroscopy ». The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu161886103349645.
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Norlin, Börje. « Characterisation and application of photon counting X-ray detector systems ». Doctoral thesis, Mittuniversitetet, Institutionen för informationsteknologi och medier, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-38.
Texte intégralRésumé :
This thesis concerns the development and characterisation of X-ray imaging systems based on single photon processing. “Colour” X-ray imaging opens up new perspectives within the fields of medical X-ray diagnosis and also in industrial X-ray quality control. The difference in absorption for different “colours” can be used to discern materials in the object. For instance, this information might be used to identify diseases such as brittle-bone disease. The “colour” of the X-rays can be identified if the detector system can process each X-ray photon individually. Such a detector system is called a “single photon processing” system or, less precise, a “photon counting system”. With modern technology it is possible to construct photon counting detector systems that can resolve details to a level of approximately 50 µm. However with such small pixels a problem will occur. In a semiconductor detector each absorbed X-ray photon creates a cloud of charge which contributes to the image. For high photon energies the size of the charge cloud is comparable to 50 µm and might be distributed between several pixels in the image. Charge sharing is a key problem since, not only is the resolution degenerated, but it also destroys the “colour” information in the image. This thesis presents characterisation and simulations to provide a detailed understanding of the physical processes concerning charge sharing in detectors from the MEDIPIX collaboration. Charge summing schemes utilising pixel to pixel communications are proposed. Charge sharing can also be suppressed by introducing 3D-detector structures. In the next generation of the MEDIPIX system, Medipix3, charge summing will be implemented. This system, equipped with a 3D-silicon detector, or a thin planar high-Z detector of good quality, has the potential to become a commercial product for medical imaging. This would be beneficial to the public health within the entire European Union.Denna avhandling berör utveckling och karaktärisering av fotonräknande röntgensystem. ”Färgröntgen” öppnar nya perspektiv för medicinsk röntgendiagnostik och även för materialröntgen inom industrin. Skillnaden i absorption av olika ”färger” kan användas för att särskilja olika material i ett objekt. Färginformationen kan till exempel användas i sjukvården för att identifiera benskörhet. Färgen på röntgenfotonen kan identifieras om detektorsystemet kan detektera varje foton individuellt. Sådana detektorsystem kallas ”fotonräknande” system. Med modern teknik är det möjligt att konstruera fotonräknande detektorsystem som kan urskilja detaljer ner till en upplösning på circa 50 µm. Med så små pixlar kommer ett problem att uppstå. I en halvledardetektor ger varje absorberad foton upphov till ett laddningsmoln som bidrar till den erhållna bilden. För höga fotonenergier är storleken på laddningsmolnet jämförbar med 50 µm och molnet kan därför fördelas över flera pixlar i bilden. Laddningsdelning är ett centralt problem delvis på grund av att bildens upplösning försämras, men framför allt för att färginformationen i bilden förstörs. Denna avhandling presenterar karaktärisering och simulering för att ge en mer detaljerad förståelse för fysikaliska processer som bidrar till laddningsdelning i detektorer från MEDIPIX-projekter. Designstrategier för summering av laddning genom kommunikation från pixel till pixel föreslås. Laddningsdelning kan också begränsas genom att introducera detektorkonstruktioner i 3D-struktur. I nästa generation av MEDIPIX-systemet, Medipix3, kommer summering av laddning att vara implementerat. Detta system, utrustat med en 3D-detektor i kisel, eller en tunn plan detektor av högabsorberande material med god kvalitet, har potentialen att kunna kommersialiseras för medicinska röntgensystem. Detta skulle bidra till bättre folkhälsa inom hela Europeiska Unionen.
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Fang, Yuan. « Monte Carlo Transport Methods for Semiconductor X-ray Imaging Detectors ». Thesis, 2013. http://hdl.handle.net/10012/7650.
Texte intégralRésumé :
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.
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Pereira, Maria Elias Lopes. « Characterization of direct X-ray Detectors based on Organic Semiconductor thin films ». Master's thesis, 2018. http://hdl.handle.net/10362/130841.
Texte intégralRésumé :
The detection of ionizing radiation such as X-rays is a constantly growing area of research thanks to its numerous application fields, which span from astrophysics, to industrial and civil security or even medical imaging and diagnostics. In this project, conducted at the University of Bologna (UNIBO), department of physics, one of the most active groups of research in this area, four different molecules (TIPS, TIPGe, diF TES ADT and diF TEG ADT) were studied as the organic semiconductor thin film in a photoconductor. The devices were realized by drop-casting a solution processed of the molecules onto three different substrates (PET, PEN and glass), for a direct approach on the detection of this radi-ation. Different parameters such as resistivity, percentage of active area covered by the molecule, quan-tity and thickness of the crystals, were investigated for their influence on the performance of the X-Ray detector.
It was found that in the PET substrate there is a process of discharge that seems to be important to the performance of the detector and that seems to induce a decrease in the current of the diF TES ADT and diF TEG ADT based devices, making them unsuitable for any kind of application.
With the PEN substrate it is possible to achieve reliable and reproducible devices with high signal to noise ratios and acceptable sensitivities.
The glass substrate with the TIPGe would be the best one because it combines a high sensitivity with a reliable and reproducible device. Nevertheless, glass is not a flexible substrate and therefore is not suitable for many of the applications of interest, for example wearable health diagnostic applications like a personal dosimeter.
Finally, it was proved that the molecules with the germanium element show, as it was expected due to the higher atomic number of Ge compared to Si, the highest sensitivities. It was also discovered that this is also due to the high quality crystals achieved with these molecules.
Given the results obtained, this line of research seems to be fruitful, with very interesting practical applications expected.A deteção de radiação ionizante, como os raios-X, é uma área de pesquisa em constante crescimento, graças aos seus vastos campos de aplicação, que abrangem desde a astrofísica, centrais nucleares, segurança industrial e civil, até ao diagnóstico médico. Neste projeto, realizado na Universidade de Bolonha, no departamento de física, um dos grupos de investigação mais ativos nesta área, quatro mo-léculas diferentes (TIPS, TIPGe, diF TES ADT e diF TEG ADT) foram estudadas na forma de filme fino orgânico semicondutor num fotocondutor. Os dispositivos foram preparados através da deposição por drop-casting de uma solução destas moléculas em três substratos (PET, PEN e vidro), para uma abordagem direta na deteção desta radiação. A influência de diferentes parâmetros, como a resistividade, percentagem de área ativa coberta pela molécula, quantidade e espessura dos cristais, foi investigada quanto ao desempenho dos detetores de raios-X. Descobriu-se que, no substrato PET, há um processo de descarga que parece ser importante para o desempenho do detetor e que aparentemente induz uma diminuição na corrente dos dispositivos base-ados em diF TES ADT e diF TEG ADT, tornando-os inadequados para qualquer tipo de aplicação. Com o substrato PEN, é possível obter dispositivos fiáveis e reprodutíveis com baixo ruído e sensibilidades aceitáveis. O substrato de vidro com o TIPGe daria o melhor dispositivo porque combina uma alta sensibilidade com um dispositivo fiável e reprodutível. No entanto, não é um substrato flexível e, portanto, não é adequado para muitas das aplicações de interesse, como por exemplo, aplicações de diagnóstico de saúde, como a dosimetria pessoal. Finalmente, ficou provado que as moléculas com o elemento germânio apresentam, como esperado pelo seu número atómico mais elevado que o do silício, as mais altas sensibilidades. Descobriu-se, ainda, que isso também se deve aos cristais de alta qualidade obtidos nessas moléculas. Em função dos resultados obtidos, a linha de investigação parece profícua, esperando-se aplicações práticas muito interessantes.
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Dědič, Václav. « Vliv hlubokých hladin na transport náboje v CdTe a CdZnTe ». Doctoral thesis, 2014. http://www.nusl.cz/ntk/nusl-342278.
Texte intégralRésumé :
CdTe and CdZnTe are promising materials for room temperature semiconductor X-ray and gamma ray detectors. The accumulation of a space charge at deep energy levels due to a band bending at contacts with Schottky barriers and due to trapped photogenerated charge may result in time dependent change of charge collection efficiency in CdTe and CdZnTe detectors known as polarization effect. This thesis is mainly focused on a study of electric field profiles in detectors under dark and high photon flux conditions simulating detector operation using crossed polarizers technique exploiting the electro-optic (Pockels) effect. It also deals with a study of deep levels responsible for the polarization and influence of contact metals on charge accumulation. Several experimental results are supported by theoretical simulations. The measurements were performed on three sets of samples equipped with different contact metals (Au, In) cut from three different n-type CdTe and CdZnTe materials. Energy levels were detected using methods based on the Pockels effect and discharge current measurements. Detailed study of internal electric field profiles has revealed a fundamental influence of near midgap energy levels related to crystal defects and contact metals on the polarization in semiconductor detectors under high radiation...
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« Thickness dependence of electron transport in amorphous selenium for use in direct conversion flat panel X-ray detectors ». Thesis, 2013. http://hdl.handle.net/10388/ETD-2013-04-950.
Texte intégralRésumé :
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.
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Shafique, Umar. « Organic Semiconductor Detector for Large Area Digital Imaging ». Thesis, 2014. http://hdl.handle.net/10012/8428.
Texte intégralRésumé :
Organic semiconductor technology has gained attention in both the sensor and display markets due to its low cost and simple fabrication techniques. The ability to fabricate organic semiconductor devices such as photodetectors and transistors on a flexible, lightweight substrate makes them less fragile and ideal candidates for portable large-area imaging applications. The use of organic semiconductor technology in large-area medical imaging can bring about a new generation of flexible and lightweight indirect X-ray imagers. These imagers are immune to mechanical shock and should be ideal for portable intraoral X-ray radiology. In order to realize these organic flexible imagers and their use in large-area medical imaging, many challenges associated with the device performance and fabrication need to be overcome. Among these challenges, one of the greatest is to improve the dark current performance of the organic semiconductor photodetectors (key for imager performance) with a high-photo to-dark current ratio. Low dark current is needed to improve the sensitivity of the imager, whereas a large photo-to-dark current ratio reduces noise in the extracted image.
Numerous techniques have been reported to improve the dark current performance in vertical organic photodetector design; however, lateral photodetectors still lack research attention. This thesis presents a lateral multilayer photodetector design and a simplified technique to improve the dark current performance of lateral organic semiconductor photodetectors. Our technique allows us to apply a large bias voltage while maintaining a low dark current, high photo-to-dark current ratio, and improves detector speed; thus, the overall sensitivity of the detector is improved.
We further show the integration of an organic photodetector with an organic backplane readout circuit to form a flexible large-area imager. This imager can be used for large-area digital imaging applications such as in medical radiology.