The optical properties of semiconductors are inextricably linked to their electronic and vibrational properties. Electronic transitions from hydrogenic impurities and vibrational modes of mass defects lead to well-defined peaks in the infrared (IR) spectrum that provide information about the symmetry and chemical composition of the defects. Optical techniques such as photoluminescence (PL) provide researchers with a (mostly) nondestructive method for identifying defects. Light can also change defects, especially those that undergo large relaxation when their charge state changes. The DX center, for example, can absorb a photon and move to its shallow-donor site, leading to persistent photoconductivity (PPC) at low temperatures. In certain perovskite oxide semiconductors, substitutional hydrogen can be optically excited, causing the proton and electrons to leave. This leads to large room temperature PPC. Similar processes may cause photochromism, which is a change in sample color after exposure to light. We discovered a remarkable example of this effect in Cu-doped β-Ga₂O₃, an ultra-wide bandgap semiconductor.

Web-link: https://labs.wsu.edu/mccluskey/

Brief Bio: Matt McCluskey is Westinghouse Professor of Materials Science and Engineering, Department of Physics and Astronomy, Washington State University (WSU). He received his Physics Ph.D. from UC Berkeley in 1997, under the supervision of Professor Eugene Haller. His research, performed at the Lawrence Berkeley National Laboratory, focused on hydrogen in semiconductors. Prof. McCluskey did postdoctoral research at Xerox PARC, where he studied semiconductors used in blue lasers, under the supervision of Dr. Noble Johnson. In August 1998, he joined the WSU faculty as an assistant professor. He has a broad research background in high-pressure and materials physics. His group is also developing optical techniques such as confocal microscopy, which resulted in a startup company, Klar Scientific.