Thesis
Characterization of Te secondary phases in cadmium zinc telluride using IR transmission microscopy
Washington State University
Master of Science (MS), Washington State University
2010
Handle:
https://hdl.handle.net/2376/103526
Abstract
CZT is considered a competitive room temperature semiconductor capable of detecting high-energy radiation such as X-rays and gamma-rays. However its maximum efficiency has yet to be attained due to extended defects such as twins, grain/multi boundaries, and other secondary phases present in a grown ingot. One of these secondary phases present in designed detectors is Te secondary phases, which is the focus of this study. Te secondary phases fall into two categories: Te precipitates and Te inclusions with average diameter of 1-75um. A fraction of a void may surround a visible Te inclusion. Otherwise observed isolated voids and Te inclusions seem present in most CZT detectors as well. These Te inclusions and voids serve as impurity sinks capable of trapping electrons. We have employed IR transmission microscopy to study Te inclusions. This study assumes that all lone Te inclusions and voids as well as inclusions surrounded by voids are simply "Te inclusions". We then found that Te inclusions with average diameter > 4um are major inhibitors of electron mobility-lifetime (MT) in a CZT detector. Te inclusions, however, are considered a litmus test which confirms favorable stiochiometry. A favorable stiochiometry can produce a better compensation scheme necessary in improving detectors' resistivity and MT value. This is because their shape, size, and distribution (SSD) make a reliable pattern for projected detector quality. While some CZT ingots grown at CMR with no count of Te inclusions have failed to produce grade radiation detectors, those with density ratio of Te inclusions with average diameter< 4um to that of all counted inclusions expressed in percent (Den< 4um /DenTotal %)> 99%, have recorded MT value close to 10-2 cm 2 /V. Based on this information, a correlation between Te inclusions' SSD and MT values of detectors within an ingot and on various ingots was established. The variation of volume % of these detectors was further established to strengthen the correlation in cases where (Den< 4um /DenTotal %)>matches and/or is relatively close. These correlations are only relevant if the crystal purity and high resistivity (>109 Ω.cm) are produced.
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Details
- Title
- Characterization of Te secondary phases in cadmium zinc telluride using IR transmission microscopy
- Creators
- W. Gitau Munge
- Contributors
- Kelvin G. Lynn (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Mechanical and Materials Engineering, School of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; Pullman, Wash. :
- Identifiers
- 99900525081601842
- Language
- English
- Resource Type
- Thesis