Analysis of critical points in temperature dependent and time resolved ellipsometry spectra of Ge using digital filtering

ORAL

Abstract

We analyze critical points (CPs) in the dielectric function (DF) of Ge measured with static and time-resolved spectroscopic ellipsometry. Data were taken between 10 K and 718 K to investigate the temperature dependence of the direct band gap E0. To obtain lineshape parameters, the second energy derivatives of the DF are calculated using a linear filter technique based on Gaussian kernels introduced by Le et. al.1 which combines interpolation, noise reduction, and scale change. Taking into account excitonic effects, a Tanguy lineshape is fitted to the second derivatives of the DF. A red shift of energy and an increase in broadening with rising temperature are found and are fitted using a Bose-Einstein factor considering electron-phonon interaction.
The same analysis method is applied to the E1 and E1+Δ1 CPs of Ge dependent on photo-excited charge carrier density obtained from femtosecond pump-probe ellipsometry measurements.2 The CP parameters are determined as functions of delay time and a change of the CP energies suggests a laser heating of about 20 K to 40 K.

1V.L. Le, T.J. Kim, Y.D. Kim, D.E. Aspnes, J. Vac. Sci. & Technol. B 37, 052903 (2019)
2S. Espinoza, S. Richter, M. Rebarz, O. Herrfurth, R. Schmidt-Grund, J. Andreasson, S. Zollner, Appl. Phys. Lett. 115, 052105 (2019)

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Presenters

  • Carola Emminger

    • Department of Physics, New Mexico State University
    • Physics, New Mexico State University
    • New Mexico State University

Authors

  • Carola Emminger

    • Department of Physics, New Mexico State University
    • Physics, New Mexico State University
    • New Mexico State University

  • Farzin Abadizaman

    • Department of Physics, New Mexico State University

  • Nuwanjula Samarasingha Arachchige

    • New Mexico State University
    • Department of Physics, New Mexico State University
    • Physics, New Mexico State University

  • Jose Menendez

    • Department of Physics, Arizona State University
    • Physics, Arizona State University

  • Shirly Espinoza

    • ELI Beamlines, Institute of Physics of the Czech Academy of Sciences

  • Steffen Richter

    • Institutionen för fysik, Linköpings University

  • Mateusz Rebarz

    • ELI Beamlines, Institute of Physics of the Czech Academy of Sciences

  • Oliver Herrfurth

    • Felix Bloch Institute for Solid State Physics, Universität Leipzig

  • Martin Zahradník

    • ELI Beamlines, Institute of Physics of the Czech Academy of Sciences

  • Rüdiger Schmidt-Grund

    • Institut für Physik, Technische Universität Ilmenau

  • Jakob Andreasson

    • ELI beamlines
    • ELI Beamlines, Institute of Physics of the Czech Academy of Sciences

  • Stefan Zollner

    • Department of Physics, New Mexico State University
    • Physics, New Mexico State University