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Proceedings Paper

Ultrafast dynamics of coherent optical phonons in GeTe/Sb2Te3 superlattices: thermal conductivity and coherent control
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Paper Abstract

We report on the evaluation of lattice thermal conductivity of GeTe/Sb2Te3 superlattice (SL) by using a coherent phonon spectroscopy at various lattice temperatures. The time-resolved transient reflectivity obtained in amorphous and crystalline GeTe/Sb2Te3 SL films exhibits the coherent A1 optical modes at terahertz (THz) frequencies with picoseconds dephasing time. The relaxation time and frequency of the coherent A1 modes are used to compute the lattice thermal conductivity based on the Debye theory, including scattering by grain boundary and point defect, umklapp process, and phonon resonant scattering. The results indicate that the thermal conductivity in the amorphous SL film is less temperature dependent, due to the dominant phonon-defect scattering, while in the crystalline SL it is temperature dependent because of the main contributions from umklapp and phonon resonant scatterings. We argue the higher thermal conductivity in the GeTe/Sb2Te3 SL films than that in the Ge2Sb2Te5 alloy films implies that the phase change in GeTe/Sb2Te3 SL is not purely promoted by thermal process, i.e., lattice heating, but rather by nonthermal process, i.e., coherent lattice excitation, because the thermal process generally requires lower thermal conductivity.

Paper Details

Date Published: 20 February 2012
PDF: 7 pages
Proc. SPIE 8260, Ultrafast Phenomena and Nanophotonics XVI, 82601G (20 February 2012); doi: 10.1117/12.908572
Show Author Affiliations
Muneaki Hase, Univ. of Tsukuba (Japan)
Junji Tominaga, National Institute of Advanced Industrial Science and Technology (Japan)

Published in SPIE Proceedings Vol. 8260:
Ultrafast Phenomena and Nanophotonics XVI
Markus Betz; Abdulhakem Y. Elezzabi; Jin-Joo Song; Kong-Thon Tsen, Editor(s)

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