Dr. Ralph B. James
Associate Laboratory Director
Science and Technology
Savannah River National Laboratory

ABSTRACT

Compound semiconductors are under investigation by many organizations for applications in the detection and imaging of X- and gamma-ray radiation. Such room-temperature-operating detectors are needed for a wide variety of medical and security uses. Among the different compound-semiconductor detectors available today, Cadmium Zinc Telluride (CdZnTe or CZT) is the most extensively studied one due to its band-gap, high atomic number, and excellent charge-carrier transport properties. A two-pronged approach to advance the technology is underway, (1) Identify and fix defects in the crystals by improving the growth and device fabrication processes, and (2) Use the best material for fabricating detectors and incorporating them into instruments for spectroscopy and imaging. We will report on the physical properties of CZT at the micro-scale level, and correlations of the crystal’s defects with device performance. A set of dedicated tools have been constructed for this R&D, including automated infrared transmission microscopy, X-ray micro-scale mapping using a synchrotron light source, X-ray transmission/refraction tomography, current deep level transient spectroscopy, and photoluminescence setups. This presentation will report some of our findings to understand the defects created during growth and surface processing, distinguish various crystal defects and their effects on carrier trapping, study the internal electrical field in detectors, clarify the effects of annealing on the detector’s properties, and deploy the detectors in instruments for detection of special nuclear materials and localization of cancerous tumors. If time permits, we will briefly describe some of our recent results on alternative semiconductor detectors also under study, e.g., CdMnTe, CdMgTe, CdTeSe and CdZnTeSe.
^*Collaborators: A. E. Bolotnikov, G. S. Camarda, Y. Cui, R Gul, V. Dedic, G. De Geronimo, J. Fried, A. Hossain, U. Roy, and G. Yang

Short Synopsis:

Dr. Ralph James serves as the Associate Laboratory Director for Science and Technology and the Chief Research Officer with DOE’s Savannah River National Laboratory. There, he manages the Laboratory’s cross-cutting S&T capabilities that provide a framework for addressing the needs of SRNL’s different business units and their customers. Previously, he served as the Associate Laboratory Director for the Energy, Environment and National Security with Brookhaven National Laboratory.  Dr. James’ R&D efforts have focused on basic and applied research devoted to semiconductor materials, radiation detectors, and imaging systems. He has co-authored more than 620 scientific publications, served as editor of 31 books, and holds 25 patents. The output of Dr. James’ research has impacted numerous applications in the fields of emerging materials, gamma-ray spectrometers, nuclear medicine, solar energy, astrophysics, and national security. He is a Fellow of the IEEE, SPIE, AAAS, OSA, MRS and APS, and he has received numerous prestigious international honors for his work on detectors and imaging, 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, Long Island Person of the Year in Science, 50 World’s Best Technologies Award, Battelle Innovation Award, Frost & Sullivan Invention of the Year, Long Technology Hall of Fame Inductee, among many others. Dr. James was also the President of SPIE, and served as Chairman of the Council of Scientific Society Presidents representing over 70 scientific societies and 1.4 million scientists and engineers across the globe.