(460e) An Analysis of Zinc Distribution During the EDG Growth of Cadmium Zinc Telluride

The availability of large, single crystals of cadmium zinc telluride (CZT) with uniform properties is key to improving the performance of gamma radiation detectors fabricated from them. However, this goal has proven to be elusive.  In this presentation, we discuss the many challenges of growing better CZT crystals and how computational modeling may favorably impact these challenges.  Our thesis is that crystal growth modeling is a powerful tool to complement experiments and characterization.  It provides an important approach to close the loop between materials discovery, device research, systems performance, and producibility. 

Specifically, we discuss heat transfer, interface shape, and zinc segregation during the electrodynamic gradient-freeze (EDG) growth of cadmium zinc telluride (CZT) using finite element models for this system.  A realistic multi-scale model has been developed to describe CZT growth in a pyrolytic boron nitride (PBN) crucible for the EDG growth system employed by the Pacific Northwest National Laboratory (PNNL).  This approach has yielded great insight into system heat transfer, melt convection, and interface shape from prior calculations.  Here, we discuss model extensions to conduct fully transient computations needed to predict the segregation of species during growth.  For the first time, detailed zinc segregation analyses are performed for this system.  Due to the small thermal gradients and strong coupling of convection with the thermal field, several different cellular flow structures evolve in time in the melt.  The transient evolution between these flow states produces markedly non-uniform segregation patterns that are unlike the simple behavior of more classical Bridgman growth systems.  This behavior is discussed and compared with available experimental data on zinc segregation in CZT grown by Bridgman methods.

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This work has been supported in part by the Department of Energy, National Nuclear Security Administration, under Award Numbers DE-FG52-06NA27498 and DE-FG52-08NA28768, the content of which does not necessarily reflect the position or policy of the United States Government, and no official endorsement should be inferred.