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Analysis of Defect Structures in 4H Silicon Carbide Bulk Crystals, Epitaxial Layers and Power Devices.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Analysis of Defect Structures in 4H Silicon Carbide Bulk Crystals, Epitaxial Layers and Power Devices./
Author:	Guo, Jianqiu.
Description:	1 online resource (150 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 80-05, Section: B.
Contained By:	Dissertations Abstracts International80-05B.
Subject:	Engineering. -
Online resource:	click for full text (PQDT)
ISBN:	9780438637726

Analysis of Defect Structures in 4H Silicon Carbide Bulk Crystals, Epitaxial Layers and Power Devices.
Guo, Jianqiu.

Analysis of Defect Structures in 4H Silicon Carbide Bulk Crystals, Epitaxial Layers and Power Devices. - 1 online resource (150 pages)

Source: Dissertations Abstracts International, Volume: 80-05, Section: B.

Thesis (Ph.D.)--State University of New York at Stony Brook, 2018.

Includes bibliographical references

Over the past decades, the revolution in power electronics technology has been moving towards systems with higher efficiency and higher power density. As conventional silicon-based devices are approaching their performance limitations, 4H silicon carbide power devices, owing to their superior material advantages, have been steadily replacing silicon in many power applications. However, the current crystalline quality of silicon carbide bulk materials as well as epitaxial layers is still one of the biggest hurdles to its widespread use. Due to its intrinsic material properties, silicon carbide is hard to grow and process-many types of crystalline defects exist in significant numbers to impair device performance. It is therefore crucial to understand the origins of these defects, to investigate their behavior, and to evaluate their impact on device operation. Synchrotron x-ray topography is one of the best techniques to characterize and analyze different types of defects in single crystals including silicon carbide. It is a non-destructive imaging tool based on the unique, powerful, high-intensity X-rays from a synchrotron light source facility. Such technique allows the ex-situ and in-situ characterization of silicon carbide crystals (as-grown or during growth/processing), enabling the reconstruction of three-dimensional defects structures and visualization of their evolution during certain processes. Studies related to the dissertation can be categorized into three major parts: (a) investigation of defects nucleated in the bulk silicon carbide crystals grown by physical vapor transport method, (b) analysis on the formation mechanism of defects in silicon carbide homoepitaxial layers grown by chemical vapor deposition method, and (c) understanding the role of defects in silicon carbide power device operation. Each category includes one or more individual studies carried out during the years of my doctoral research. A condensed summary is given below for each study: 1) Threading mixed dislocations are mixed type growth dislocations with both axial and basal plane components and are commonly observed in silicon carbide bulk materials. In this study, the use of synchrotron x-ray topography to determine both the line directions and the Burgers vectors of such dislocations is demonstrated. The determination of dislocation line direction is done via synchrotron white beam x-ray topography and this method is based on the fact that the projected line directions of dislocations on different reflections are different. The determination of the absolute Burgers vectors is demonstrated as well, in which synchrotron monochromatic beam x-ray topography is combined with ray tracing simulation. This method utilizes the fact that the contrast from dislocations varies on topographic images as their Burgers vectors change. Results show that most of the threading dislocations that were previously regarded as pure screw dislocations are actually of mixed type. 2) While basal plane slip is the most frequently observed deformation mechanism in 4H silicon carbide crystals grown by PVT method, prismatic slip of dislocations has also been reported previously. In this study, an observation of three equivalent sets of prismatic dislocations was made in a commercial wafer using synchrotron white beam x-ray topography. Each set of prismatic dislocations is distributed non-uniformly depending on the distribution of resolved shear stress on each prismatic slip system. A thermal model is developed where the thermal stresses induced by radial temperature gradients during bulk growth are estimated. Result from the thermal modelling shows good correlation with the topographic observation, which confirms that radial thermal gradients play a key role in activating prismatic slip in 4H silicon carbide. 3) The presence of lattice strain in silicon carbide substrate crystals method can strongly influence the performance of related power devices that are fabricated on them. Information on the level and the variation of lattice strain in these wafer crystals is thus important. In this study, a non-destructive method-synchrotron double-crystal contour mapping is developed to map lattice strains in 4H silicon carbide wafers. The theory of this technique is reviewed followed by the demonstration on a commercial silicon carbide substrate material. Analysis of the strain maps shows that the lattice dilation/compression, rather than lattice tilt, is the major type of deformation in this wafer. Discussions are made regarding different modes of measurement and corresponding spatial resolution and sensitivity. 4) During silicon carbide homoepitaxy and post-growth annealing, the process of stress relaxation was previously reported to lead to the formation of interfacial dislocations. Such a relaxation process has been extensively studied for decades. Major models related to relaxation are reviewed. In this study, an in-situ characterization of relaxation process during high temperature treatment of a silicon carbide homoepitaxial wafer was made, where the formation of interfacial dislocation was dynamically observed. During the treatment, the wafer was heated locally to a temperature as high as the epitaxy growth temperature. (Abstract shortened by ProQuest.).

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9780438637726Subjects--Topical Terms:

561152
Engineering.
Subjects--Index Terms:

CharacterizationIndex Terms--Genre/Form:

554714
Electronic books.

Analysis of Defect Structures in 4H Silicon Carbide Bulk Crystals, Epitaxial Layers and Power Devices.
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504 $a Includes bibliographical references
520 $a Over the past decades, the revolution in power electronics technology has been moving towards systems with higher efficiency and higher power density. As conventional silicon-based devices are approaching their performance limitations, 4H silicon carbide power devices, owing to their superior material advantages, have been steadily replacing silicon in many power applications. However, the current crystalline quality of silicon carbide bulk materials as well as epitaxial layers is still one of the biggest hurdles to its widespread use. Due to its intrinsic material properties, silicon carbide is hard to grow and process-many types of crystalline defects exist in significant numbers to impair device performance. It is therefore crucial to understand the origins of these defects, to investigate their behavior, and to evaluate their impact on device operation. Synchrotron x-ray topography is one of the best techniques to characterize and analyze different types of defects in single crystals including silicon carbide. It is a non-destructive imaging tool based on the unique, powerful, high-intensity X-rays from a synchrotron light source facility. Such technique allows the ex-situ and in-situ characterization of silicon carbide crystals (as-grown or during growth/processing), enabling the reconstruction of three-dimensional defects structures and visualization of their evolution during certain processes. Studies related to the dissertation can be categorized into three major parts: (a) investigation of defects nucleated in the bulk silicon carbide crystals grown by physical vapor transport method, (b) analysis on the formation mechanism of defects in silicon carbide homoepitaxial layers grown by chemical vapor deposition method, and (c) understanding the role of defects in silicon carbide power device operation. Each category includes one or more individual studies carried out during the years of my doctoral research. A condensed summary is given below for each study: 1) Threading mixed dislocations are mixed type growth dislocations with both axial and basal plane components and are commonly observed in silicon carbide bulk materials. In this study, the use of synchrotron x-ray topography to determine both the line directions and the Burgers vectors of such dislocations is demonstrated. The determination of dislocation line direction is done via synchrotron white beam x-ray topography and this method is based on the fact that the projected line directions of dislocations on different reflections are different. The determination of the absolute Burgers vectors is demonstrated as well, in which synchrotron monochromatic beam x-ray topography is combined with ray tracing simulation. This method utilizes the fact that the contrast from dislocations varies on topographic images as their Burgers vectors change. Results show that most of the threading dislocations that were previously regarded as pure screw dislocations are actually of mixed type. 2) While basal plane slip is the most frequently observed deformation mechanism in 4H silicon carbide crystals grown by PVT method, prismatic slip of dislocations has also been reported previously. In this study, an observation of three equivalent sets of prismatic dislocations was made in a commercial wafer using synchrotron white beam x-ray topography. Each set of prismatic dislocations is distributed non-uniformly depending on the distribution of resolved shear stress on each prismatic slip system. A thermal model is developed where the thermal stresses induced by radial temperature gradients during bulk growth are estimated. Result from the thermal modelling shows good correlation with the topographic observation, which confirms that radial thermal gradients play a key role in activating prismatic slip in 4H silicon carbide. 3) The presence of lattice strain in silicon carbide substrate crystals method can strongly influence the performance of related power devices that are fabricated on them. Information on the level and the variation of lattice strain in these wafer crystals is thus important. In this study, a non-destructive method-synchrotron double-crystal contour mapping is developed to map lattice strains in 4H silicon carbide wafers. The theory of this technique is reviewed followed by the demonstration on a commercial silicon carbide substrate material. Analysis of the strain maps shows that the lattice dilation/compression, rather than lattice tilt, is the major type of deformation in this wafer. Discussions are made regarding different modes of measurement and corresponding spatial resolution and sensitivity. 4) During silicon carbide homoepitaxy and post-growth annealing, the process of stress relaxation was previously reported to lead to the formation of interfacial dislocations. Such a relaxation process has been extensively studied for decades. Major models related to relaxation are reviewed. In this study, an in-situ characterization of relaxation process during high temperature treatment of a silicon carbide homoepitaxial wafer was made, where the formation of interfacial dislocation was dynamically observed. During the treatment, the wafer was heated locally to a temperature as high as the epitaxy growth temperature. (Abstract shortened by ProQuest.).
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650 4 $a Materials science. $3 557839
653 $a Characterization
653 $a Crystal growth
653 $a Defect structures
653 $a Silicon carbide
653 $a Wide bandgap semiconductor
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