Coherent gigahertz phonons in Ge2Sb2Te5 phase-change materials

Muneaki Hase, Paul Fons, Alexander V. Kolobov, Junji Tominaga

Research output: Contribution to journalArticle

Abstract

Using ≃ 40 fs ultrashort laser pulses, we investigate the picosecond acoustic response from a prototypical phase change material, thin Ge2Sb2Te5 (GST) films with various thicknesses. After excitation with a 1.53 eV-energy pulse with a fluence of ≃ 5 mJ cm?2, the time-resolved reflectivity change exhibits transient electronic response, followed by a combination of exponential-like strain and coherent acoustic phonons in the gigahertz (GHz) frequency range. The time-domain shape of the coherent acoustic pulse is well reproduced by the use of the strain model by Thomsen et al 1986 (Phys. Rev. B 34 4129). We found that the decay rate (the inverse of the relaxation time) of the acoustic phonon both in the amorphous and in the crystalline phases decreases as the film thickness increases. The thickness dependence of the acoustic phonon decay is well modeled based on both phonon-defect scattering and acoustic phonon attenuation at the GST/Si interface, and it is revealed that those scattering and attenuation are larger in crystalline GST films than those in amorphous GST films.

Original languageEnglish
Article number485402
JournalJournal of Physics Condensed Matter
Volume27
Issue number48
DOIs
Publication statusPublished - 2015 Nov 16
Externally publishedYes

Keywords

  • femtosecond laser
  • phase-change materials
  • phonon scattering

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics

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