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Excitation and detection of coherent optical phonon modes in epitaxial cubic Ge2Sb2Te5thin films of different crystallographic orientation

Published online by Cambridge University Press:  13 February 2014

R. Al-Saigh ,
A. Shalini ,
G. P. Srivastava ,
R. J. Hicken  and
R. Calarco
R. Al-Saigh
Affiliation:
School of Physics and Astronomy, University of Exeter, Exeter EX4 4QL, UK
A. Shalini
Affiliation:
School of Physics and Astronomy, University of Exeter, Exeter EX4 4QL, UK
G. P. Srivastava
Affiliation:
School of Physics and Astronomy, University of Exeter, Exeter EX4 4QL, UK
R. J. Hicken
Affiliation:
School of Physics and Astronomy, University of Exeter, Exeter EX4 4QL, UK
R. Calarco
Affiliation:
Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany
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Abstract

Optical pump-probe studies of cubic crystalline Ge2Sb2Te5/GaSb(001) have previously shown that the amplitude of a coherent optical phonon (COP) with frequency of 3.4 THz observed in the anisotropic reflectance (AR) signal exhibits a four-fold dependence upon the polarization of the probe beam. The appearance of the mode in the AR signal but not the reflectance (R) signal, and the dependence upon probe polarization, both suggest a three-dimensional mode character. Confirmation that this mode indeed has three-dimensional character, similar to the Raman inactive T2 mode in the pristine rock salt structure, is highly important in understanding the structure of the crystalline phase of Ge2Sb2Te5 that has important applications within data storage technology. A phonon of the same frequency has been observed in an epitaxial Ge2Sb2Te5/InAs(111) structure, suggesting that this phonon is indeed characteristic of epitaxial cubic GST. A theory, which considers the symmetry of the Raman tensor for a particular phonon mode, is used to predict the dependence of R and AR signal amplitude upon pump and probe polarization for the T2 mode of a (111) facet of the putative rock-salt structure.

Keywords

opticalphotoreflectanceRaman spectroscopy
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1661: Symposium UU – Phonon-Interaction-Based Materials Design—Theory, Experiments and Applications , 2014 , mrsf13-1661-uu08-07
Copyright
Copyright © Materials Research Society 2014 

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References

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