Crystals of cadmium zinc telluride (CZT) typically exhibit significant populations of large (10 micron and above) tellurium-rich particles that are deleterious to the performance of semiconductor radiation detectors.  While it is well understood that melt growth of CZT can produce crystalline material that is supersaturated with tellurium, providing a thermodynamic basis for the existence of these second-phase particles, their formation mechanisms are not well understood.  

As an alternative to preventing particle formation during the growth process (which may not be possible), an interesting post-growth treatment may provide a means to higher-quality crystals.  Namely, these large, tellurium-enriched, secondary-phase particles can be induced to move away from a region of grown crystal and accumulate elsewhere, leaving higher-quality regions that contain far fewer particles. This accomplished by heating the sample to slightly above the eutectic temperature (the melting point of the second-phase particles) and engineering a temperature gradient across the sample. Under such conditions, the now-liquid particle dissolves on the hot side and re-solidifies on the cool side, with a net effect of migrating toward the hotter region.  This process is termed “temperature gradient zone melting,” or TGZM.

We will present the formulation and implementation of steady-state and dynamic models that employ the Galerkin finite element method and elliptic mesh generation techniques to solve for particle migration via TGZM.  Such an approach is particularly well suited for rigorous and accurate representation of geometrical and interfacial interactions in this system.  We will also present initial results to verify the model and identify the dominant physical interactions involved in this process.  We will also compare preliminary model results with data currently being taken on TGZM applied to CZT crystals in experiments at Brookhaven National Laboratories conducted by collaborators at Alabama A&M University.

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1. A Comprehensive Model of the Growth of Cadmium Zinc Telluride (CZT) by the Traveling Heater Method (THM)
2. Modeling the Migration of Tellurium-Rich, Second-Phase Particles in Cadmium Zinc Telluride (CZT) via Temperature Gradient Zone Melting (TGZM)
3. Modeling of Particle Engulfment during the Growth of Multicrystalline Silicon for Solar Cells
4. Combined interface attachment kinetics and transport phenomena in large scale solution growth systems
5. The Horizontal Ribbon Growth Process for Solar Silicon: Analysis of Stability and Segregation
6. Toward Controlling Interface Shape during Bridgman Crystal Growth: Past, Present, and Future
7. Analysis of Scintillator Crystal Production via the Edge-Defined Film-Fed Growth Method
8. Analysis of a Traveling Magnetic Field (TMF) on Bridgman Crystal Growth of Cadmium Zinc Telluride (CZT)
9. Analysis of the Nonlinear Behavior of Detached Bridgman Growth in Microgravity
10. Modeling of Particle Engulfment during the Growth of Multicrystalline Silicon for Solar Cells
11. A Comprehensive Model of the Growth of Cadmium Zinc Telluride (CZT) by the Traveling Heater Method (THM)
12. Modeling the Migration of Tellurium-Rich, Second-Phase Particles in Cadmium Zinc Telluride (CZT) via Temperature Gradient Zone Melting (TGZM)