Vince Lordi, Keith Ray, Kyoung Kweon, Joel Varley, Daniel Åberg
Collaborators: Nicole Adelstein (San Francisco Statue University), Paul Erhart (Chalmers, Sweden), Cedric Rocha Leão (Univ. Fed. ABC, Brazil), Kuang-Jen Wu, Adam Conway, Lars Voss, Steve Payne (LLNL)
Efficient and accurate detection of high-energy radiation, particularly gamma and X rays, is important for national security, space imaging, medical imaging, scientific diagnostics, and other applications. Particularly for national security applications, where a large number of moderately inexpensive high-performance detectors are required, high energy-resolution is desired along with operation at room temperature. To achieve high performance in detectors using a semiconductor as the active material, the semiconductor must possess high carrier mobilities, long carrier lifetimes, high resistivity, a moderate band gap (approximately 1.4 to 2.2 eV), and high average atomic number. These requirements often conflict and also depend heavily on extrinsic properties of the crystals, such as the presence of various defects. Our work focuses on using ab initio methods to model the properties of defects in semiconductors at multiple scales to understand both fundamental and process limitations of materials for room-temperature gamma detection. We have applied these methods to a number of materials—including AlSb, GaTe, CdTe, CdZnTe, and TlBr—to assess process options for optimizing performance and achieving required specifications, and we work with experimental teams to validate and test predictions of optimal growth and process conditions.