Skip to main content

Excitation and detection of coherent optical phonon modes in epitaxial cubic Ge2Sb2Te5 thin films of different crystallographic orientation


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.

This is a preview of subscription content, access via your institution.


  1. K. Makino, J. Tominaga, A. V. Kolobov, P. Fons and M. Hase, Appl. Phys. Lett. 101, 232101 (2012).

    Article  Google Scholar 

  2. M. Forst, T. Dekorsy, C. Trappe, M. Laurezis and H. Kurz, Appl. Phys. Lett. 77, 1964 (2000).

    Article  CAS  Google Scholar 

  3. M. Hase, Y. Miyamoto and J. Tominaga, Phys. Rev. B 79, 174112 (2009).

    Article  Google Scholar 

  4. D. Lencer, M. Salinga, and M. Wuttig, Adv.Mater. XX, 1 (2011).

    Google Scholar 

  5. A. Shalini, Y. Liu, U. Al-Jarah, G. P. Srivastava, C. D. Wright, F. Katmis, W. Braun and R. J. Hicken, Scientific Report 3, 2965 (2013).

    Article  CAS  Google Scholar 

  6. R. Merlin, Solid State Communications. 102, 207(1007).

    Article  Google Scholar 

  7. F. Kathmis {etet al.}, Cryst. Growth and Design, (2011).

    Google Scholar 

  8. A. Shalini, “Ultrafast Optical Studies of Phonons and Phase Transitions in Ge2Sb2Te5 thin films,” (Ph. D. thesis, University of Exeter, 2013).

    Google Scholar 

  9. T. Dekorsy, G. Cheon Cho and H. Kurz, Light Scattering in Solid. 76, 169 (2000).

    Article  CAS  Google Scholar 

  10. R. Loudon, Advances in Physics 50, 813 (2001).

    Article  Google Scholar 

Download references


RAS acknowledges financial support from King Saud University in the Kingdom of Saudi Arabia.

Author information

Authors and Affiliations


Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Al-Saigh, R., Shalini, A., Srivastava, G.P. et al. Excitation and detection of coherent optical phonon modes in epitaxial cubic Ge2Sb2Te5 thin films of different crystallographic orientation. MRS Online Proceedings Library 1661, 22–27 (2014).

Download citation

  • Published:

  • Issue Date:

  • DOI: