3 results
Current Status of the Quality of 4H-SiC Substrates and Epilayers for Power Device Applications
- M. Dudley, H. Wang, Jianqiu Guo, Yu Yang, Balaji Raghothamachar, J. Zhang, B. Thomas, G. Chung, E. K. Sanchez, D. Hansen, S. G. Mueller
-
- Journal:
- MRS Advances / Volume 1 / Issue 2 / 2016
- Published online by Cambridge University Press:
- 26 January 2016, pp. 91-102
- Print publication:
- 2016
-
- Article
- Export citation
-
Interfacial dislocations (IDs) and half-loop arrays (HLAs) present in the epilayers of 4H-SiC crystal are known to have a deleterious effect on device performance. Synchrotron X-ray Topography studies carried out on n-type 4H-SiC offcut wafers before and after epitaxial growth show that in many cases BPD segments in the substrate are responsible for creating IDs and HLAs during CVD growth. This paper reviews the behaviors of BPDs in the substrate during the epitaxial growth in different cases: (1) screw-oriented BPD segments intersecting the surface replicate directly through the interface during the epitaxial growth and take part in stress relaxation process by creating IDs and HLAs (Matthews-Blakeslee model [1] ); (2) non-screw oriented BPD half loop intersecting the surface glides towards and replicates through the interface, while the intersection points convert to threading edge dislocations (TEDs) and pin the half loop, leaving straight screw segments in the epilayer and then create IDs and HLAs; (3) edge oriented short BPD segments well below the surface get dragged towards the interface during epitaxial growth, leaving two long screw segments in their wake, some of which replicate through the interface and create IDs and HLAs. The driving force for the BPDs to glide toward the interface is thermal stress and driving force for the relaxation process to occur is the lattice parameter difference at growth temperature which results from the doping concentration difference between the substrate and epilayer.
3 - Factors limiting reproductive success in the giant panda as revealed by a Biomedical Survey
-
- By Susie Ellis, Conservation International, Donald Lo Janssen, San Diego Zoo, Zoological Society of San Diego, Mark S. Edwards, San Diego Zoo, Zoological Society of San Diego, Jogayle Howard, National Zoological Park, Guangxin He, Chengdu Research Base of Giant Panda Breeding, Jianqiu Yu, Chengdu Research Base for Giant Panda Breeding, Guiquan Zhang, China Research and Conservation Center for the Giant Panda, Rongping Wei, China Conservation and Research Center for the Giant Panda, R. Eric Miller, Saint Louis Zoo, WildCare Institute, David E. Wildt, National Zoological Park
- Edited by David E. Wildt, Smithsonian National Zoological Park, Washington DC, Anju Zhang, Hemin Zhang, Wildlife Conservation and Research Center for Giant Pandas, Donald L. Janssen, Zoological Society of San Diego, Susie Ellis
-
- Book:
- Giant Pandas
- Published online:
- 09 August 2009
- Print publication:
- 27 July 2006, pp 37-58
-
- Chapter
- Export citation
-
Summary
INTRODUCTION
There is surprisingly little published information about giant panda biology, especially in the life sciences. This poor quantity (and quality) of data has been due primarily to too few individual animals available for study and a traditional hands-off policy towards hands-on research in such a rare and high-profile species. However, recent changes (see Chapter 2) have created important, new opportunities for giant panda investigations. People responsible for ensuring that the species survives now realise that giant pandas living in zoos and breeding centres are a valuable research resource (see Chapter 1). It also has been recognised that this population must be intensively managed if it is truly to support giant pandas that are surviving precariously in nature. The intended result will be an ever-increasing amount of new, scholarly information and sufficient panda numbers to continue educating the public, helping to raise conservation funding, serving as a hedge against extinction, and even as a source of animals for potential reintroductions. However, these laudable goals can only be achieved by first understanding and then rigorously managing the captive population so that it becomes demographically and genetically stable. This, in fact, has become the mantra of Chinese managers of the ex situ population: ‘to develop a self-sustaining, captive population of giant pandas that will assist supporting a long-term, viable population in the wild’ (see Chapter 2).
4 - Significant medical issues and biological reference values for giant pandas from the Biomedical Survey
-
- By Donald L. Janssen, San Diego Zoo, Zoological Society of San Diego, Mark S. Edwards, San Diego Zoo, Zoological Society of San Diego, Meg Sutherland-Smith, San Diego Zoo, Zoological Society of San Diego, Jianqiu Yu, Chengdu Research Base for Giant Panda Breeding, Desheng Li, China Conservation and Research Center for the Giant Panda, Guiquan Zhang, China Research and Conservation Center for the Giant Panda, Rongping Wei, China Conservation and Research Center for the Giant Panda, Cheng Lin Zhang, Beijing Zoo, R. Eric Miller, Saint Louis Zoo, WildCare Institute, Lyndsay G. Phillips, School of Veterinary Medicine, Daming Hu, China Conservation and Research Center for the Giant Panda, Chunxiang Tang, China Conservation and Research Center for the Giant Panda
- Edited by David E. Wildt, Smithsonian National Zoological Park, Washington DC, Anju Zhang, Hemin Zhang, Wildlife Conservation and Research Center for Giant Pandas, Donald L. Janssen, Zoological Society of San Diego, Susie Ellis
-
- Book:
- Giant Pandas
- Published online:
- 09 August 2009
- Print publication:
- 27 July 2006, pp 59-86
-
- Chapter
- Export citation
-
Summary
INTRODUCTION
The Giant Panda Biomedical Survey sought to establish a baseline of scientific information on giant pandas living in Chinese zoos and breeding centres as a first step towards establishing a self-sustaining captive population (Zheng et al., 1997; see also Chapter 2). To produce the most information that would allow an understanding of the health and reproductive status of the extant population, we chose an interdisciplinary approach to examine as many health and reproductive traits as possible. What was crucial was the trusting relationship that developed early in the process between the Chinese and American teams which led to a thorough understanding of giant panda biology – information that not only was fascinating from a scholarly perspective but also valuable to improving ex situ management.
This chapter provides detailed methods and medical findings following the assessment of more than 60% of the living Chinese population of giant pandas (as existed in 1996 when the need for a Biomedical Survey was recognised). The results in this chapter address issues ranging from disease conditions to reproductive compromise, all of which ultimately allowed classifying each animal as to its usefulness in achieving the goal of population self-sustainability. The practices and reference values described here will also be useful to those who are interested in closely studying and managing giant pandas in the future.