(285b) Analysis of a Traveling Magnetic Field (TMF) for Active Control of the Bridgman Growth of CZT Crystals

Large, single crystals of cadmium zinc telluride (CZT) are needed for portable, low-cost, and sensitive devices to monitor radioactive materials.  However, while CZT improvements are needed, the growth of these crystals is not well understood. We aim to advance the practice of crystal growth by applying physics-based, computational process models along with modern process control theory. Specifically, we are developing model-based control for the growth of cadmium zinc telluride crystals via the Bridgman method.

In this presentation, we describe a novel approach that may be employed to actively control features of CZT growth in Bridgman systems, namely the application of a traveling magnetic field (TMF).  The application of TMF produces Lorentz forces through the molten phase, and these forces can be tuned in magnitude and spatial orientation to profoundly impact melt flows.  In turn, these flows modify heat and mass transfer, influencing the shape of the melt-solid interface and segregation along the interface.  Since the applied TMF can be instantaneously changed, it provides for a potentially ideal control action, if its complicated effects can be predicted and understood. This is the immediate goal of our work; we discuss the mathematical formulation of our TMF analysis and, more importantly, our initial results on the effects of TMF applied to a prototypical CZT growth system.