Crystallization of Ge2Sb2Te5 thin films by nano- and femtosecond single laser pulse irradiation

Xinxing Sun, Martin Ehrhardt, Andriy Lotnyk, Pierre Lorenz, Erik Thelander, Jürgen W. Gerlach, T. Smausz, Ulrich Decker, Bernd Rauschenbach

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Abstract

The amorphous to crystalline phase transformation of Ge2Sb2Te5 (GST) films by UV nanosecond (ns) and femtosecond (fs) single laser pulse irradiation at the same wavelength is compared. Detailed structural information about the phase transformation is collected by x-ray diffraction and high resolution transmission electron microscopy (TEM). The threshold fluences to induce crystallization are determined for both pulse lengths. A large difference between ns and fs pulse irradiation was found regarding the grain size distribution and morphology of the crystallized films. For fs single pulse irradiated GST thin films, columnar grains with a diameter of 20 to 60 nm were obtained as evidenced by cross-sectional TEM analysis. The local atomic arrangement was investigated by high-resolution Cs-corrected scanning TEM. Neither tetrahedral nor off-octahedral positions of Ge-atoms could be observed in the largely defect-free grains. A high optical reflectivity contrast (∼25%) between amorphous and completely crystallized GST films was achieved by fs laser irradiation induced at fluences between 13 and 16 mJ/cm2 and by ns laser irradiation induced at fluences between 67 and 130 mJ/cm2. Finally, the fluence dependent increase of the reflectivity is discussed in terms of each photon involved into the crystallization process for ns and fs pulses, respectively.

Original languageEnglish
Article number28246
JournalScientific Reports
Volume6
DOIs
Publication statusPublished - Jun 13 2016

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crystallization
fluence
irradiation
thin films
pulses
lasers
transmission electron microscopy
phase transformations
reflectance
high resolution
x ray diffraction
grain size
scanning electron microscopy
thresholds
defects
photons
wavelengths
atoms

ASJC Scopus subject areas

  • General

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Sun, X., Ehrhardt, M., Lotnyk, A., Lorenz, P., Thelander, E., Gerlach, J. W., ... Rauschenbach, B. (2016). Crystallization of Ge2Sb2Te5 thin films by nano- and femtosecond single laser pulse irradiation. Scientific Reports, 6, [28246]. https://doi.org/10.1038/srep28246

Crystallization of Ge2Sb2Te5 thin films by nano- and femtosecond single laser pulse irradiation. / Sun, Xinxing; Ehrhardt, Martin; Lotnyk, Andriy; Lorenz, Pierre; Thelander, Erik; Gerlach, Jürgen W.; Smausz, T.; Decker, Ulrich; Rauschenbach, Bernd.

In: Scientific Reports, Vol. 6, 28246, 13.06.2016.

Research output: Contribution to journalArticle

Sun, X, Ehrhardt, M, Lotnyk, A, Lorenz, P, Thelander, E, Gerlach, JW, Smausz, T, Decker, U & Rauschenbach, B 2016, 'Crystallization of Ge2Sb2Te5 thin films by nano- and femtosecond single laser pulse irradiation', Scientific Reports, vol. 6, 28246. https://doi.org/10.1038/srep28246
Sun, Xinxing ; Ehrhardt, Martin ; Lotnyk, Andriy ; Lorenz, Pierre ; Thelander, Erik ; Gerlach, Jürgen W. ; Smausz, T. ; Decker, Ulrich ; Rauschenbach, Bernd. / Crystallization of Ge2Sb2Te5 thin films by nano- and femtosecond single laser pulse irradiation. In: Scientific Reports. 2016 ; Vol. 6.
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