Measuring Photoexcited Electron and Hole Dynamics in ZnTe and Modeling Excited State Core-Valence Effects in Transient Extreme Ultraviolet Reflection Spectroscopy
Transient extreme ultraviolet (XUV) spectroscopy is becoming a valuable tool for characterizing solar energy materials because it can separate photoexcited electron and hole dynamics with element specificity. Here, we use surface-sensitive femtosecond XUV reflection spectroscopy to separately measure photoexcited electron, hole, and band gap dynamics of ZnTe, a promising photocathode for CO₂ reduction. We develop an ab initio theoretical framework based on density functional theory and the Bethe–Salpeter equation to robustly assign the complex transient XUV spectra to the material's electronic states. Applying this framework, we identify the relaxation pathways and quantify their time scales in photoexcited ZnTe, including subpicosecond hot electron and hole thermalization, surface carrier diffusion, ultrafast band gap renormalization, and evidence of acoustic phonon oscillations.
© 2023 American Chemical Society. This material is based on work performed by the Liquid Sunlight Alliance, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub, under Grant DE-SC0021266. The computations presented here were conducted in the Resnick High Performance Computing Center, a facility supported by the Resnick Sustainability Institute at the California Institute of Technology. Ground state optical absorption and XPS data were collected at the Molecular Materials Research Center in the Beckman Institute of the California Institute of Technology. I.M.K. and J.L.M. acknowledge support by the National Science Foundation Graduate Research Fellowship Program under Grant 1745301. Author Contributions. H.L. and J.M.M. contributed equally to this work. The authors declare no competing financial interest.
Supplemental Material - jz2c03894_si_001.pdf