ACT/SGER: Evaluation of a Novel Approach for Improved Growth of CdZnTe

This project addresses crystal growth of CdZnTe, a material useful as a portable, low-cost, and sensitive means to monitor radioactive materials via the detection of emitted gamma rays. There are several technologies for gamma detectors, such as classical sodium iodide (NaI) scintillation devices and liquid-nitrogen-cooled Germanium detectors. However, gamma detectors based on cadmium zinc telluride (CdZnTe) offer unique advantages: 1. CdZnTe operates as a direct detector, thereby allowing for the design of small detection probes and portable devices. 2. CdZnTe devices work at room temperature, thus avoiding cooling technology. 3. Since CdZnTe detectors have a much better resolution compared to NaI detectors, they are the only room temperature detectors that allow hand-held and portable devices to provide a detection of radioactive signatures behind significant lead or steel shieldings. Low cost, large-area, single crystals with low compositional variation and homogeneous electrical properties are sought. Currently, the growth of large, single crystals of CdZnTe is accomplished by the Bridgman method and is notoriously difficult. These crystals typically exhibit rather poor crystalline perfection, significant concentrations of large defects, and poor uniformity of Zn concentration. The objective of this project is to apply large-scale numerical simulation to assess an alternative growth configuration for CdZnTe - a destabilizing vertical Bridgman configuration rather than the classical stabilizing configuration. While counter intuitive and exploratory, this new growth technique may allow for dramatic improvements in CdZnTe substrate quality and process yields, and provides new understanding of bulk crystal growth processes.

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The project addresses fundamental research issues associated with electronic/photonic materials having technological relevance. An important feature of the project is education and training, with emphasis on integration of research and education. The project aids in the development of the scientific workforce by exposing students to technical issues important for the security of the nation. Other broader impacts include relevance to the ACT program and potential advances in nuclear medical imaging devices, digital radiography, and high-resolution astrophysical imaging. Additionally, the understanding learned form this project will be applicable to the growth of other crystalline materials via the Bridgman method.

This award is supported jointly by the NSF and the Intelligence Community. The Approaches to Combat Terrorism (ACT) Program in the Directorate for Mathematics and Physical Sciences supports new concepts in basic research and workforce development with the potential to contribute to national security.