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Book Simulation and Growth of Cadmium Zinc Telluride from Small Seeds by the Travelling Heater Method

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 Directory of Graduate Research

Download or read book Directory of Graduate Research written by American Chemical Society. Committee on Professional Training and published by . This book was released on 2005 with total page 1932 pages. Available in PDF, EPUB and Kindle. Book excerpt: Faculties, publications and doctoral theses in departments or divisions of chemistry, chemical engineering, biochemistry and pharmaceutical and/or medicinal chemistry at universities in the United States and Canada.

Book Large Volume Single Crystal Growth of Cadmium Zinc Telluride with Minimal Secondary Phases for Room Temperature Radiation Detector Application

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 Dissertation Abstracts International

Download or read book Dissertation Abstracts International written by and published by . This book was released on 2004 with total page 740 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Strategies and Challenges to Improve Single Crystal Yield and Detector Properties of Cadmium Zinc Telluirde that Is Telluride Grown Via Accelerated Crucible Rotation

Download or read book Strategies and Challenges to Improve Single Crystal Yield and Detector Properties of Cadmium Zinc Telluirde that Is Telluride Grown Via Accelerated Crucible Rotation written by Saketh Kakkireni and published by . This book was released on 2020 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt: Solid-state radiation detection finds its applications in numerous fields ranging from nuclear medicine to astrophysics. Although Semiconductors offer better energy and spatial resolution than Scintillators, their market share is limited by the cost, availability and need for cryogenic cooling. Cadmium Zinc Telluride (CZT) is a compound semiconductor with attractive properties for compact device technology for detection of X-rays and Gamma-rays. Over the past few decades' numerous efforts are made to grow high-quality CZT, unfortunately to-date it's application is limited by large-scale production and cost. Poor thermo-physical properties of CZT coupled with no strong growth direction make it a challenge to achieve high yield of single crystalline material. Current industrial flux growth technique is inherently limited by slow growth rates and requires post-processing. The solution may be found in the Accelerated Crucible Rotation Technique (ACRT), where the crystal growth is achieved under a forced convective regime involving periodic rotation of the growth crucible. ACRT induced flow patterns can homogenize the melt thereby enabling faster growth rates and eliminate the need for post-processing. Our preliminary results, presented here, show that ACRT can reduce the production time by a factor of four. Additionally, the application of ACRT has provided the potential for scale up the growth process. Also discussed are challenges and future strategies in ACRT coupled CZT growth. Successful completion of this work will enable the use of CZT in the next generation imaging systems as well as provide a better foundation for understanding and implementing ACRT in other crystal growth systems. Successful seeding and superior detector resolutions are demonstrated.

Book Development of Traveling Heater Method to Grow Cadmium Telluride CdTe Cadmium Zinc Telluride CZT Crystals

Download or read book Development of Traveling Heater Method to Grow Cadmium Telluride CdTe Cadmium Zinc Telluride CZT Crystals written by Manchanahalli S. Rohan Rao and published by . This book was released on 2011 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Strategic Approaches Towards Solving Critical Challenges in Crystal Growth of Detector Grade Cd0 9Zn0 1Te Including Melt Mixing Techniques

Download or read book Strategic Approaches Towards Solving Critical Challenges in Crystal Growth of Detector Grade Cd0 9Zn0 1Te Including Melt Mixing Techniques written by Amlan Datta and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the last few decades Cadmium Zinc Telluride (CZT) has emerged as a novel material for radiation detection in homeland security as well as medical applications and as substrates for epitaxial growth of infrared detector, Mercury Cadmium Telluride. There are, however, several critical issues regarding the bulk growth of CZT which renders it unsuitable or cost ineffective for these applications. These challenges can be summarized as non-uniformity (due to Zinc and intentional dopant segregation), longer growth times (because of lower thermal conductivity of the melt), Tellurium (Te) secondary phases (SP), unstable growth interface (due to lower thermal conductivity and higher heat of fusion) and non-stoichiometric growth conditions. Systematic approaches towards solving these problems will be discussed along with the consequences and future research directions.

Book Implementation of Accelerated Crucible Rotation in Electrodynamic Gradient Freeze Method for Highly Non stoichiometric Melt Growth of Cadmium Zinc Telluride Detectors

Download or read book Implementation of Accelerated Crucible Rotation in Electrodynamic Gradient Freeze Method for Highly Non stoichiometric Melt Growth of Cadmium Zinc Telluride Detectors written by Jedidiah Jacob McCoy and published by . This book was released on 2018 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cadmium Zinc Telluride (CZT) is a semiconducting material well known in the high energy radiation detection community for its virtues as a solid state radiation detector. Its application is broad, spanning homeland security, nonproliferation, medical physics, and astrophysics. Unfortunately, difficulty in producing detector grade CZT in appreciable quantities has greatly limited its economic success. Several decades have been spent on overcoming this production issue, but with little success. At present, the traveling heater method (THM) is most widely used for industrial growth applications as it can produce detector grade material with acceptable yields. However, CZT growth rates in THM remain relatively slow, and post-growth processing is required resulting in long, economically disadvantaged timescales. On the other hand, melt growth techniques, such as vertical Bridgman (VB) and its modifications, are capable of much faster growth rates, but suffer from low yields and poor reproducibility. Additionally, electron mobility lifetime (microtaue) products from VB grown CZT have traditionally been an order of magnitude lower than THM grown CZT. Even so, because of its fast growth rate, VB is the ideal candidate to achieve economic success in CZT production if reproducible material yield and competitive microtau e products can be achieved. To accomplish this, the following set of issues inherent to melt growth of CZT must be addressed: inhomogeneity in Zn and dopant concentrations, the presence of second phase defects, low single crystal yield, and high impurity content. This dissertation will outline the development of a mode for bulk CZT production via VB method capable of overcoming these four melt growth issues. Accelerated Crucible Rotation (ACRT) was implemented during growth in order to homogenize the melt and adjust interface stability. A systematic study was conducted with computational guidance to optimize ACRT parameters. Melt stoichiometry was adjusted to enhance ACRT mixing as well as adjust maximum growth temperatures and improve overall purity. Temperature profile and material handling procedures were optimized as well. The developed method is capable of producing highly competitive detector grade CZT material with unprecedented yields on economically viable timescales.

Book Material Properties of Large volume Cadmium Zinc Telluride Crystals and Their Relationship to Nuclear Detector Performance

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 Annual Report

    Annual Report

    Book Details:
  • Author :
  • Publisher :
  • Release : 2013
  • ISBN :
  • Pages : 7 pages

Download or read book Annual Report written by and published by . This book was released on 2013 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of this project is to develop growth models of CZT crystals from the melt using vertical gradient freeze (VGF) or vertical Bridgman growth as a typical process. Further, the project will perform critical experiments including single crystal growth to validate the growth models and to provide detailed data for modeling and simulation. Ideally, the project will develop growth models that will provide, for the first time, choices for optimal CZT single crystal growth from the melt based on model input. The overarching goal that guides this research proposal is to produce large, single crystals of CZT with good yield and reproducible properties. In our view this depends on 1) understanding crystal growth processes, including annealing and cool-down processing, and 2) understanding the role of defects on detector response since it is not possible, yet, to produce defect-free materials. Models of defect structure and formation are addressed. Validated models and experiments on reducing defects in melt-grown crystals are used to guide our understanding of growth processes and in-furnace annealing plus cool-down.