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HL: Fachverband Halbleiterphysik

HL 30: Ultrafast Phenomena II

HL 30.3: Talk

Wednesday, March 20, 2024, 10:30–10:45, EW 015

Transient core-hole screening investigated by time-resolved X-ray absorption spectroscopy at the Zn K-edge of ZnO — •Thomas C. Rossi¹, Lu Qiao², Keith Gilmore², Ronaldo Rodrigues Pelà², Claudia Draxl², and Renske M. van der Veen¹ — ¹Helmholtz Zentrum Berlin für Materialien und Energie GmbH, 14109 Berlin, Germany — ²Department Physics and IRIS Adlershof, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany

Understanding the ultrafast electronic and lattice response of photoexcited semiconductor materials at the atomic level is crucial for the realization and optimization of devices. Here, we report on the picosecond dynamics of atoms and photoexcited charge carriers above the optical band gap of ZnO in oriented nanorods and thin films by time-resolved X-ray absorption spectroscopy (TRXAS) at the Zn K-edge. The transient signal reveals the non-local screening of the core-hole potential by photogenerated electron-hole pairs, often overlooked in previous studies on photoexcited semiconductors. State-of-the-art calculations with the Bethe Salpeter equation are able to reproduce the spectral features and the non-linear effect of the core-hole screening on the transient with the excitation density. Theoretical predictions are made on the effect of the pump/probe polarization and efficiency of the non-local screening on the femtosecond timescale. This work highlights the simultaneous sensitivity of TRXAS to incoherent atomic motions and delocalized photoexcited carriers with chemical element sensitivity, which opens new perspectives for the study of photoexcited semiconductors in complex materials or in optoelectronic devices.

Keywords: ultrafast spectroscopy; X-ray absorption spectroscopy; zinc oxide; screening; Bethe Salpeter