Ralph James of Savannah River National Laboratory

Cadmium zinc telluride (CZT) is the most promising semiconductor material today for production of X-ray and gamma detectors and imaging arrays operable at room temperature. The performance of CZT devices, the global capacity for growth of detector-grade crystals, and the size of the commercial market have progressed steadily over the past few years. Concurrently, the cost for CZT gamma-ray spectrometers has decreased. Unfortunately, because of deficiencies in the quality of the material, high-resolution CZT spectrometers are still limited to relatively small dimensions (< 1 cm3), which makes them inefficient at detecting high photon energies and somewhat ineffective for weak radiation signals except in near proximity. Despite the current constraints on efficiency of the devices, CZT detectors have been increasingly deployed in medical, space, environment, and national security applications for monitoring and imaging radiation in the energy range of 2-2000 keV. The detectors could be attractive for a much broader range of applications; however, increases in their efficiency are needed without sacrificing the ability to spectrally resolve X-ray and gamma energies. Achieving the goal of low-cost efficient CZT detectors requires progress in the following areas: growth of larger crystals, reductions in carrier trapping, increases in the electrical resistivity, better uniformity of device response, and improved device fabrication procedures. This talk will summarize the material factors limiting the performance of CZT gamma-ray detectors and discuss ways to overcome them through appropriate corrections in the crystal growth and device fabrication processes.

Ralph James of Savannah River National Laboratory

This study provides a technical roadmap to enable the pursuit of R&D on compound semiconductor radiation detectors more intensely by addressing materials challenges deemed as the greatest strategic value to multiple user communities. A Working Group (WG) composed of ~30 experts in the field of radiation detection and imaging was formed to assess past progress on the development of semiconductor radiation detectors, evaluate the current status of materials R&D, envision the future state of the most promising detector materials, identify knowledge gaps that must be addressed to achieve these future states, and prioritize the R&D needs based on maximizing the impact.  The scope of this presentation will be limited to X- and gamma-ray detectors, although recommendations to advance semiconductor neutron detectors, charged particle detectors, and photodetectors were also pursued. This presentation will be divided along three distinct phases: (1) An assessment and ranking of the most important accomplishments in the field, (2) Consensus opinions regarding the most promising candidate materials to increase detection efficiency, improve energy resolution, and lower cost, and (3) Top ten prioritized materials R&D directions (PRD#1 – PRD#10) to achieve the desired performance goals for the leading semiconductors. These PRDs are designed to improve crystal growth processes, purification, fabrication steps, robustness to operating conditions, detector stability, and manufacturing. Each represents significant R&D with well-defined outcomes, ideally leading to breakthroughs in the scalable growth, purification, and fabrication strategies needed to achieve monolithic detector-grade crystals of 50-100 cm3. Implementation of these priorities is expected to more fully unlock the potential of semiconductor detectors for a variety of uses. Additional details of these high-priority research directions will be given in the presentation.

Biography:

Ralph James received the M.S. and Ph.D. degrees in Applied Physics from Caltech. His R&D has focused on semiconductor materials, gamma-ray and neutron radiation detectors, nonproliferation, national security and nuclear medicine. He is a Fellow of the IEEE, SPIE, AAAS, Optica, MRS and APS. Dr. James has authored >740 scientific publications, served as editor of 36 books, and holds 27 patents. He has received numerous prestigious honors, including Discover Magazine Innovator of the Year, 7 R&D100 awards, IEEE Outstanding Radiation Instrumentation Award, IEEE Harold Wheeler Award, Room-Temperature Semiconductor Scientist Award, Battelle Innovation Award, Frost & Sullivan Invention of the Year, Long Technology Hall of Fame Inductee, ARCS Hall of Fame Inductee, Long Island Person of Year, among many others. He was also the President of SPIE and Chairman of the Council of Scientific Society Presidents representing over 70 scientific societies and 1.4 million scientists/engineers.