Transient birefringence and dichroism in ZnO studied with fs-time-resolved spectroscopic ellipsometry

O. Herrfurth, S. Richter, M. Rebarz, S. Espinoza, J. Zúñiga-Pérez, C. Deparis, J. Leveillee, A. Schleife, M. Grundmann, J. Andreasson, R. Schmidt-Grund

Research output: Contribution to journalArticlepeer-review

Abstract

The full transient dielectric-function (DF) tensor of ZnO after UV-laser excitation in the spectral range 1.4-3.6 eV is obtained by measuring an m-plane-oriented ZnO thin film with femtosecond (fs)-time-resolved spectroscopic ellipsometry. From the merits of the method, we can distinguish between changes in the real and the imaginary part of the DF as well as changes in birefringence and dichroism, respectively. We find pump-induced switching from positive to negative birefringence in almost the entire measured spectral range for about 1 ps. Simultaneously, weak dichroism in the spectral range below 3.0 eV hints at contributions of inter-valence-band transitions. Line-shape analysis of the DF above the band gap based on discrete exciton, exciton-continuum, and exciton-phonon-complex contributions shows a maximal dynamic increase in the transient exciton energy by 80 meV. The absorption coefficient below the band gap reveals an exponential line shape attributed to Urbach-rule absorption mediated by exciton-longitudinal-optic-phonon interaction. The transient DF is supported by first-principles calculations for 1020cm-3 excited electron-hole pairs in ideal bulk ZnO.

Original languageEnglish (US)
Article number013246
JournalPhysical Review Research
Volume3
Issue number1
DOIs
StatePublished - Mar 16 2021

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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