Improved High Z, Wide Band Gap Semiconductors through Modeling and Experiment

Nuclear Nonproliferation, first responders, and security personnel need to detect and identify radioactive threats. Gamma-ray spectrometers provide the information needed for these missions, however, most detectors are either too expensive or impractical for portable use. Unfortunately advances in new and emerging detector materials are slow due to the unguided “trial-and-error” processes typically used. The effort proposed here will develop a theoretical framework to understand these materials and guide the optimization process to dramatically reduce the time to bring new detectors to market. Phase I, we will initiate a joint modeling and experimental approach to investigate the effects of defects on performance and long term stability of thallium bromide (TlBr) and cesium lead bromide (CsPbBr3), both high Z, wide band gap semiconductors that show great promise in filling the need for better performance at a reduced cost. Phase I will focus on understanding and controlling defects. This effort will be carried out collaboration with Sandia National Laboratory, MIT and Northwestern University. The goal of Phase I is to develop the theoretical framework to understand the properties and factors limiting performance of room temperature semiconductor radiation detector materials, and guide the optimization process to dramatically reduce the time to bring new detectors to market. The Technical objectives of Phase I are: improve the existing Sandia Molecular Dynamics model applied to TlBr to investigate and understand the effects of defects on TlBr performance, perform simulations to assess the effect of strain hardening on the motion of dislocations and the associated vacancy migration, and approaches to mitigate it, experimentally validate the modeling by performing experiments guided by the model, identify issues in CsBr3 that can be addressed theoretically. Improved detectors will replace existing products and open new markets. The markets for this technology include Homeland Security, Military, Nuclear Power, Medical Imaging, and Scientific Research. A major benefit beyond commercial will be the availability of better detectors for the military, Customs and Border Patrol, security personnel, and first responders to more quickly and more accurately locate and identify threat nuclear sources and weapons.