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 (µτe) 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 µτ 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.
|Advisor:||Lynn, Kelvin G.|
|Commitee:||McCloy, John S., McCluskey, Matthew D., Yoo, Choong-Shik|
|School:||Washington State University|
|School Location:||United States -- Washington|
|Source:||DAI-B 79/11(E), Dissertation Abstracts International|
|Subjects:||Engineering, Materials science|
|Keywords:||ACRT, Bridgman, CdTe, CdZnTe, Excess Te, Te inclusions|
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