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Surface And Bulk Defects In Cadmium Zinc Telluride And Cadmium Manganese Telluride Crystals
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Book Synopsis Surface and Bulk Defects in Cadmium Zinc Telluride and Cadmium Manganese Telluride Crystals by : Oluseyi Stephen Babalola
Download or read book Surface and Bulk Defects in Cadmium Zinc Telluride and Cadmium Manganese Telluride Crystals written by Oluseyi Stephen Babalola and published by . This book was released on 2009 with total page 139 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Material Properties of Large-volume Cadmium Zinc Telluride Crystals and Their Relationship to Nuclear Detector Performance by :
Download or read book Material Properties of Large-volume Cadmium Zinc Telluride Crystals and Their Relationship to Nuclear Detector Performance written by and published by . This book was released on 1997 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: The material showing the greatest promise today for production of large-volume gamma-ray spectrometers operable at room temperature is cadmium zinc telluride (CZT). Unfortunately, because of deficiencies in the quality of the present material, high-resolution CZT spectrometers have thus far been limited to relatively small dimensions, which makes them inefficient at detecting high photon energies and ineffective for weak radiation signals except in near proximity. To exploit CZT fully, it will be necessary to make substantial improvements in the material quality. Improving the material involves advances in the purity, crystallinity, and control of the electrical compensation mechanism. Sandia National Laboratories, California, in close collaboration with US industry and academia, has initiated efforts to develop a detailed understanding of the underlying material problems limiting the performance of large volume gamma-ray spectrometers and to overcome them through appropriate corrections therein. A variety of analytical and numerical techniques are employed to quantify impurities, compositional and stoichiometric variations, crystallinity, strain, bulk and surface defect states, carrier mobilities and lifetimes, electric field distributions, and contact chemistry. Data from these measurements are correlated with spatial maps of the gamma-ray and alpha particle spectroscopic response to determine improvements in the material purification, crystal growth, detector fabrication, and surface passivation procedures. The results of several analytical techniques will be discussed. The intended accomplishment of this work is to develop a low-cost, high-efficiency CZT spectrometer with an active volume of 5 cm3 and energy resolution of 1--2% (at 662 keV), which would give the US a new field capability for screening radioactive substances.
Book Synopsis Material and Detector Properties of Cadmium Manganese Telluride (Cd1-xMnxTe) Crystals Grown by the Modified Floating-zone Method by :
Download or read book Material and Detector Properties of Cadmium Manganese Telluride (Cd1-xMnxTe) Crystals Grown by the Modified Floating-zone Method written by and published by . This book was released on 2014 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: We demonstrated the material- and radiation-detection properties of cadmium manganese telluride (Cd1-xMnxTe; x=0.06), a wide-band-gap semiconductor crystal grown by the modified floating-zone method. We investigated the presence of various bulk defects, such as Te inclusions, twins, and dislocations of several as-grown indium-doped Cd1-xMnxTe crystals using different techniques, viz., IR transmission microscopy, and chemical etching. We then fabricated four planar detectors from selected CdMnTe crystals, characterized their electrical properties, and tested their performance as room-temperature X- and gamma-ray detectors. Thus, our experimental results show that CMT crystals grown by the modified floating zone method apparently are free from Te inclusions. However, we still need to optimize our growth parameters to attain high-resistivity, large-volume single-crystal CdMnTe.
Book Synopsis Properties of Narrow Gap Cadmium-based Compounds by : Peter Capper
Download or read book Properties of Narrow Gap Cadmium-based Compounds written by Peter Capper and published by IET. This book was released on 1994 with total page 648 pages. Available in PDF, EPUB and Kindle. Book excerpt: This highly structured volume contains sections on growth and device aspects of mercury cadmium telluride (MCT).
Book Synopsis Large Volume Single Crystal Growth of Cadmium Zinc Telluride with Minimal Secondary Phases for Room Temperature Radiation Detector Application by : Santosh Kumar Swain
Download or read book Large Volume Single Crystal Growth of Cadmium Zinc Telluride with Minimal Secondary Phases for Room Temperature Radiation Detector Application written by Santosh Kumar Swain and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Two major aspects of Cadmium Zinc Telluride (CdZnTe) crystal growth for room temperature radiation detection application namely tellurium rich second phase defects and single crystal yield have been addressed. Various approaches were considered towards the minimization of these defects both during growth and post growth thermal treatment in cadmium environment. Since the issue of retrograde solubility in CdZnTe pseudo binary alloy system causes tellurium precipitation, different cooling mechanisms were also devised to achieve minimal secondary phases. Some important and encouraging results were obtained relative to the size and distribution of secondary phases upon growing the crystal with different growth rate and different cooling rate of the crystal after growth. Thermomigration of tellurium were also observed while post processing samples in a temperature gradient, in (Cd, Zn) atmosphere. Results indicated orders of magnitude reduction on secondary phases at the expense of sample resistivity.
Book Synopsis Crystal Properties as Influenced by Crystallographic Imperfection (Cadmium Telluride). by : Guenter H. Schwuttke
Download or read book Crystal Properties as Influenced by Crystallographic Imperfection (Cadmium Telluride). written by Guenter H. Schwuttke and published by . This book was released on 1973 with total page 83 pages. Available in PDF, EPUB and Kindle. Book excerpt: The report consists of two parts. Part 1 reports a chemical-mechanical approach for generating damage-free and highly specular surfaces on single crystal and polycrystalline cadmium telluride and zinc selenide. The polishing agent is a clear solution of potassium bromide, sodium hypochlorite, sodium carbonate and water. Polishing is achieved by forming a reaction product on the primary surface, removing the reaction product, and exposing a new and fresh primary surface for continuing chemical action. Large perfect surfaces are thus obtained. Part 2 is concerned with the application of transmission electron microscopy, x-ray topography, and precision lattice parameter measurements to the characterization of cadmium telluride. New specimen preparation techniques were developed making the application of such techniques to the characterization of cadmium telluride possible. The defect structure of cadmium telluride crystals is resolved. Major defects are dislocation and tellurium inclusions. Measurement of lattice parameter, x-ray density, and thermal coefficient of expansion of CdTe are reported. (Author).
Book Synopsis Bulk Uniformity of Cadmium Zinc Telluride (CZT) Crystals for Large Volume Co-Planar Gamma Spectrometers by :
Download or read book Bulk Uniformity of Cadmium Zinc Telluride (CZT) Crystals for Large Volume Co-Planar Gamma Spectrometers written by and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Global Modeling of Bulk Crystal Growth of Cadmium Zinc Telluride in Industrial VB/VGF Systems by : Arun Pandy
Download or read book Global Modeling of Bulk Crystal Growth of Cadmium Zinc Telluride in Industrial VB/VGF Systems written by Arun Pandy and published by . This book was released on 2004 with total page 762 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Simulation and Growth of Cadmium Zinc Telluride from Small Seeds by the Travelling Heater Method by : Jordan Douglas Roszmann
Download or read book Simulation and Growth of Cadmium Zinc Telluride from Small Seeds by the Travelling Heater Method written by Jordan Douglas Roszmann and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The semiconducting compounds CdTe and CdZnTe have important applications in high-energy radiation detectors and as substrates for infrared devices. The materials offer large band gaps, high resistivity, and excellent charge transport properties; however all of these properties rely on very precise control of the material composition. Growing bulk crystals by the travelling heater method (THM) offers excellent compositional control and fewer defects compared to gradient freezing, but it is also much slower and more expensive. A particular challenge is the current need to grow new crystals onto existing seeds of similar size and quality. Simulations and experiments are used in this work to investigate the feasibility of growing these materials by THM without the use of large seed crystals. A new fixed-grid, multiphase finite element model was developed based on the level set method and used to calculate the mass transport regime and interface shapes inside the growth ampoule. The diffusivity of CdTe in liquid tellurium was measured through dissolution experiments, which also served to validate the model. Simulations of tapered THM growth find conditions similar to untapered growth with interface shapes that are sensitive to strong thermosolutal convection. Favourable growth conditions are achievable only if convection can be controlled. In preliminary experiments, tapered GaSb crystals were successfully grown by THM and large CdTe grains were produced by gradient freezing. Beginning with this seed material, 25 mm diameter CdTe and CdZnTe crystals were grown on 10 mm diameter seeds, and 65 mm diameter CdTe on 25 mm seeds. Unseeded THM growth was also investigated, as well as ampoule rotation and a range of thermal conditions and ampoule surface coatings. Outward growth beyond one or two centimeters was achieved only at small diameters and included secondary grains and twin defects; however, limited outward growth of larger seeds and agreement between experimental and numerical results suggest that tapered growth may be achievable in the future. This would require active temperature control at the base of the crystal and reduction of convection through thermal design or by rotation of the ampoule or applied magnetic fields.
Book Synopsis Study on Thermal Annealing of Cadmium Zinc Telluride (CZT) Crystals by :
Download or read book Study on Thermal Annealing of Cadmium Zinc Telluride (CZT) Crystals written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Cadmium Zinc Telluride (CZT) has attracted increasing interest with its promising potential as a room-temperature nuclear-radiation-detector material. However, different defects in CZT crystals, especially Te inclusions and dislocations, can degrade the performance of CZT detectors. Post-growth annealing is a good approach potentially to eliminate the deleterious influence of these defects. At Brookhaven National Laboratory (BNL), we built up different facilities for investigating post-growth annealing of CZT. Here, we report our latest experimental results. Cd-vapor annealing reduces the density of Te inclusions, while large temperature gradient promotes the migration of small-size Te inclusions. Simultaneously, the annealing lowers the density of dislocations. However, only-Cd-vapor annealing decreases the resistivity, possibly reflecting the introduction of extra Cd in the lattice. Subsequent Te-vapor annealing is needed to ensure the recovery of the resistivity after removing the Te inclusions.
Book Synopsis Defect Characterization in 4% Cadmium Zinc Telluride Semiconductors by : Silvia I. Penkova
Download or read book Defect Characterization in 4% Cadmium Zinc Telluride Semiconductors written by Silvia I. Penkova and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis presents a characterization study of Cadmium Zinc Telluride with a 4% Zinc molar concentration using five different techniques. Three of the characterization methods - X-ray diffraction (XRD), transmission electron microscopy (TEM) and wet chemical etching - were used to study the atomic arrangement of the lattice and the type of defects in the material. On the other hand, the other two methods - photoluminescence (PL) and the Hall Effect - provided information about the electronic properties of the material and identified the electronic signatures of the defects present. This thesis study applied these five methods to 29 samples with the [111] and [211] crystal orientations. XRD was used to calculate the Zn concentration and the atomic spacing of the samples. TEM allowed to map the crystal structure using Kikuchi diffraction and to calculate the variation of the local lattice constant. This showed that the sample was under strain. A CBED imaging condition producing HOLZ lines allowed for qualitatively imaging the strain field in the crystal and contrast phase imaging showed stacking faults and dislocations present in the lattice. Next, wet chemical etching - using Nakagawa and Everson solutions - revealed several different types of etch pits were present on the material's surface and provided a value for the etch pit density (EPD). PL at room temperature was used to calculate the Zn concentration and to produce contour maps of the samples showing the variation in Zn. Low temperature PL was used to conduct intensity and thermal studies of the material providing information about the type of emission (donor-acceptor pair, free exciton or excitonic) and the activating energies. This information was used to assign the peaks seen in the PL spectrum at 8K. Lastly, the Hall Effect experiment was used to calculate the resistivity and the mobility of carriers, i.e., electrons and holes, of the samples. The last stage of the project was to seek correlations between the data obtained during the five characterization techniques. Correlations were noted between the XRD FWHM broadening and the EPD, the disturbances in the atomic lattice and the defect band broadening and a summary of all the values calculated during the project was provided. Overall this project provided a very thorough study of 4% CZT.
Book Synopsis Photoluminescence Characterization of Cadmium Zinc Telluride by : Mohamed Alshal
Download or read book Photoluminescence Characterization of Cadmium Zinc Telluride written by Mohamed Alshal and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The demand for wide bandgap semiconductors for radiation detector applications has significantly increased in recent years due to an ever-growing need for safeguard measures and medical imaging systems amongst other applications. The need for these devices to be portable and efficient, and to operate at room temperature is important for practical applications. For radiation detectors, the semiconductor materials are mainly required to have an optimal energy gap, high average atomic number, good electrical resistivity and charge transport properties as well as purity and homogeneity. Cadmium zinc telluride (CZT) distinctly stands out among the other choices of semiconductor materials for radiation detector applications, due to its attractive material properties and the room temperature operation possibility. A tremendous amount of research is being conducted to improve CZT technology and its implementation into more commercial systems. Applications of CZT detector technology in national security, high energy physics, nuclear spectroscopy, and medical imaging systems are of special interests. However, CZT devices still face challenges that need to be understood and overcome in order to have more efficient radiation detector systems. One such challenge lies in the understanding of the surfaces of CZT detectors and surface recombination effects on charge transport, charge collection efficiency, and detector performance. Another common issue is the degradation of CZT detectors due to the presence of defects which can act as traps for the charge carriers and cause incomplete charge collection from the detectors. Thus, a major challenge is that, the commercial CZT crystals have large concentrations of defects and impurities that need to be characterized, and their effects on the detector performance should be studied. Photoluminescence (PL) spectroscopy is a sensitive, non-contact and non-destructive method, suitable to characterize lower concentrations of point defects, such as substitutional impurities (donors, acceptors) and native defects in CZT crystals. A PL spectrum provides information regarding the defect nature of the crystal by determining the presence and the type of vacancies, interstitials, and impurities in the lattice. The main objective of this thesis is to address the presence of the defects in CZT crystals, identify their types, and study their roles in the performance of x-ray radiation detectors using PL spectroscopy. Additionally, using PL method and different excitation sources including UV excitation, this thesis studies the surface of CZT samples and investigates the PL signature of the surface oxide of the samples, in an effort to optimize the surface processing and thereby improve CZT detector performance.
Book Synopsis Surface Treatment and Protection Method for Cadmium Zinc Telluride Crystals by :
Download or read book Surface Treatment and Protection Method for Cadmium Zinc Telluride Crystals written by and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A method for treatment of the surface of a CdZnTe (CZT) crystal that provides a native dielectric coating to reduce surface leakage currents and thereby, improve the resolution of instruments incorporating detectors using CZT crystals. A two step process is disclosed, etching the surface of a CZT crystal with a solution of the conventional bromine/methanol etch treatment, and after attachment of electrical contacts, passivating the CZT crystal surface with a solution of 10 w/o NH.sub. 4 F and 10 w/o H.sub. 2 O.sub. 2 in water.
Book Synopsis Uniformity and Defects in Cadmium Zinc Telluride X-ray by : James E. Toney
Download or read book Uniformity and Defects in Cadmium Zinc Telluride X-ray written by James E. Toney and published by . This book was released on 1998 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Developments in Cadmium Zinc Telluride Crystal Growth, Sample Preparation and Characterisation [sic] Techniques by : Amlan Datta
Download or read book Developments in Cadmium Zinc Telluride Crystal Growth, Sample Preparation and Characterisation [sic] Techniques written by Amlan Datta and published by . This book was released on 2010 with total page 97 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Research and Development on Single Crystal High Resistivity Cadmium Telluride for Use as a Gamma-ray Spectrometer by : Kenneth R. Zanio
Download or read book Research and Development on Single Crystal High Resistivity Cadmium Telluride for Use as a Gamma-ray Spectrometer written by Kenneth R. Zanio and published by . This book was released on 1971 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Method for Surface Passivation and Protection of Cadmium Zinc Telluride Crystals by :
Download or read book Method for Surface Passivation and Protection of Cadmium Zinc Telluride Crystals written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A method for reducing the leakage current in CZT crystals, particularly Cd.sub. 1-x Zn.sub.x Te crystals (where x is greater than equal to zero and less than or equal to 0.5), and preferably Cd.sub.0.9 Zn.sub.0.1 Te crystals, thereby enhancing the ability of these crystal to spectrally resolve radiological emissions from a wide variety of radionuclides. Two processes are disclosed. The first method provides for depositing, via reactive sputtering, a silicon nitride hard-coat overlayer which provides significant reduction in surface leakage currents. The second method enhances the passivation by oxidizing the CZT surface with an oxygen plasma prior to silicon nitride deposition without breaking the vacuum state.
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