Intelligent Heat Flow Control for (Cd,Zn)Te Crystal Growth

Improvement in the quality, size and cost of cadmium zinc telluride, (Cd,Zn)Te, substrates is necessary in order to realize the high performance benefits of HgCdTe based infrared devices. To meet this need we propose an innovative feedback control strategy for vertical Bridgman (VB) crystal growth. Using a computational heat flow model we will formulate a control algorithm that will be coupled with a novel means for manipulating the heat flow during crystal growth. The problem area we are addressing is the ability to actively control the crystal/melt interface shape in the VB configuration to maintain a flat or slightly convex (with respect to the liquid) profile. By doing so, it will be possible to grow crystals with larger diameters and lower defect densities since the potential for stacking faults, twinning and stresses due to radial thermal gradients will be reduced. To achieve the goal of high quality (Cd,Zn)Te growth we have assembled a team that combines state-of-the-art heat flow modeling capabilities, crystal growth experience, and thermal hardware design expertise. Our approach implements a logical developmental process that will lead to the production of improved (Cd,Zn)Te substrates. Anticipated Benefits: There is a constant need to establish more robust manufacturing processes in several areas of IR detector production. The goals presented in this proposed research relate directly to achieving better quality substrate materials which is fundamental to improving overall IR detector producibility and reliability.