Type
Text
Type
Thesis
Advisor
Dudley, Michael | Venkatesh, T. A.. | Raghothamachar, Balaji
Date
2013-12-01
Keywords
characterization, defect, semiconducotr, wide bandgap, X-ray topography | Materials Science
Department
Department of Materials Science and Engineering.
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/76347
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
While the mature and well-established silicon technology, though after a long marvelous progress, exhibits some critical limitations with respect to its switching frequency, operation temperature, high power reliability and efficiency, a new generation of semiconductors, commonly referred to as " wide bandgap semiconductors" , has emerged as promising candidate substrate materials that bear the capabilities to overcome those performance limitations. The inherent superior properties of those novel materials help broaden the extensions of semiconductor devices applications beyond those have been made from conventional materials like silicon, indium phosphide, and gallium arsenide. Potential revolutionary improvements coming into the cost, size, weight and performance of numerous incredible applications in both military and commercial field have already occurred and could be foreseen continued in the near future by the development of wide bandgap semiconductors. As two important representatives in the class of wide bandgap semiconductors, silicon carbide (SiC) and aluminum nitride (AlN) are mainly studied in this thesis. New electronic devices based on SiC have demonstrated outstanding performance under extreme conditions such as high power, high temperature and high frequency. Due to the material's remarkable properties like high breakdown field, high efficiency power switching capability and high temperature reliability, no doubt it has huge potentiality in the applications of microelectronic systems. Besides the rather higher bandgap that also makes it ideal candidate for the substrates in high power electronic devices, AlN's unique property--its wide direct transition energy range in ultraviolet has benefits in the realization of ultraviolet opto-electronic devices. Though they have lots of advantages, the widespread commercial availability of these two materials remains retarded by the availability of large size commercial single crystal wafers of high quality at affordable price. Either for SiC or AlN, bulk crystal growth is no easy issue, for they cannot be manufactured in volume via the common liquid methods as utilized for Si wafer produce, due to the extreme conditions needed to melt them. Both of them are primarily grown in a unique way where vapor phase is involved, namely physical vapor transport (PVT) growth technique. Since devices based on substrates with fewer defects have been demonstrated to have better performance, it is of great importance to obtain highly effective characterization techniques in order to get a better understanding of defect behavior. By analyzing the generation as well as the propagation mechanism, optimized growth strategies might be provided to help reduce or even eliminate those defects. The major techniques introduced in this thesis is synchrotron white beam X-ray topography (SWBXT) and it is in comparison with another frequently used technique--chemical etching. Nomarski optical microscope is also used complimentarily. Two main topics covered in the thesis are: 1) Measurements of BPD densities in 4-inch 4H-SiC commercial wafers assessed using both KOH etching and topography methods are compared. The ratio of the BPD density calculated from topographic images to that from etch pits is estimated to be larger than 1/sinθ , where θ is the offcut angle of the wafer. Based on the orientations of the defects in the wafers, a theoretical model is proposed to explain this disparity and two main sources of errors in assessing the BPD density using chemical etching are discussed. 2) The defect categories and distributions have been studied for six AlN single crystal wafers grown by sublimation recondensation technique. Transmission geometry in SWBXT of 3×{11-20}&3×{1-100}six reflections are carried out to map defects. Grazing-incidence reflection topography has also been taken for some selected areas for detailed analysis. Nomarski optical microscopy is used to supplement topography. | While the mature and well-established silicon technology, though after a long marvelous progress, exhibits some critical limitations with respect to its switching frequency, operation temperature, high power reliability and efficiency, a new generation of semiconductors, commonly referred to as " wide bandgap semiconductors" , has emerged as promising candidate substrate materials that bear the capabilities to overcome those performance limitations. The inherent superior properties of those novel materials help broaden the extensions of semiconductor devices applications beyond those have been made from conventional materials like silicon, indium phosphide, and gallium arsenide. Potential revolutionary improvements coming into the cost, size, weight and performance of numerous incredible applications in both military and commercial field have already occurred and could be foreseen continued in the near future by the development of wide bandgap semiconductors. As two important representatives in the class of wide bandgap semiconductors, silicon carbide (SiC) and aluminum nitride (AlN) are mainly studied in this thesis. New electronic devices based on SiC have demonstrated outstanding performance under extreme conditions such as high power, high temperature and high frequency. Due to the material's remarkable properties like high breakdown field, high efficiency power switching capability and high temperature reliability, no doubt it has huge potentiality in the applications of microelectronic systems. Besides the rather higher bandgap that also makes it ideal candidate for the substrates in high power electronic devices, AlN's unique property--its wide direct transition energy range in ultraviolet has benefits in the realization of ultraviolet opto-electronic devices. Though they have lots of advantages, the widespread commercial availability of these two materials remains retarded by the availability of large size commercial single crystal wafers of high quality at affordable price. Either for SiC or AlN, bulk crystal growth is no easy issue, for they cannot be manufactured in volume via the common liquid methods as utilized for Si wafer produce, due to the extreme conditions needed to melt them. Both of them are primarily grown in a unique way where vapor phase is involved, namely physical vapor transport (PVT) growth technique. Since devices based on substrates with fewer defects have been demonstrated to have better performance, it is of great importance to obtain highly effective characterization techniques in order to get a better understanding of defect behavior. By analyzing the generation as well as the propagation mechanism, optimized growth strategies might be provided to help reduce or even eliminate those defects. The major techniques introduced in this thesis is synchrotron white beam X-ray topography (SWBXT) and it is in comparison with another frequently used technique--chemical etching. Nomarski optical microscope is also used complimentarily. Two main topics covered in the thesis are: 1) Measurements of BPD densities in 4-inch 4H-SiC commercial wafers assessed using both KOH etching and topography methods are compared. The ratio of the BPD density calculated from topographic images to that from etch pits is estimated to be larger than 1/sinθ , where θ is the offcut angle of the wafer. Based on the orientations of the defects in the wafers, a theoretical model is proposed to explain this disparity and two main sources of errors in assessing the BPD density using chemical etching are discussed. 2) The defect categories and distributions have been studied for six AlN single crystal wafers grown by sublimation recondensation technique. Transmission geometry in SWBXT of 3×{11-20}&3×{1-100}six reflections are carried out to map defects. Grazing-incidence reflection topography has also been taken for some selected areas for detailed analysis. Nomarski optical microscopy is used to supplement topography. | 55 pages
Recommended Citation
Sun, Shun, "Defects Analysis of Wide Bandgap Semiconductor Single Crystals via Synchrotron White Beam X-ray Topography" (2013). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 2271.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/2271