Excitation and detection of coherent optical phonon modes in epitaxial cubic Ge2Sb2Te5thin films of different crystallographic orientation. Issue 1661 (13th February 2014)

• Record Type: Journal Article
• Authors: Al-Saigh, R.; Shalini, A.; Srivastava, G. P.; Hicken, R. J.; Calarco, R.
• Is Part Of: MRS proceedings. Issue 1661:(2014)
• Publication Date: 2014-02-13
• Subjects: optical, -- photoreflectance, -- Raman spectroscopy; Electrical engineering -- Congresses; Physics -- Congresses; Materials -- Research -- Congresses; Materials science -- Congresses; 620.11
• DOI: 10.1557/opl.2014.185
• Languages: English
• ISSNs: 0272-9172

Abstract

ABSTRACT: Optical pump-probe studies of cubic crystalline Ge2 Sb2 Te5 /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 T 2 mode in the pristine rock salt structure, is highly important in understanding the structure of the crystalline phase of Ge2 Sb2 Te5 that has important applications within data storage technology. A phonon of the same frequency has been observed in an epitaxial Ge2 Sb2 Te5 /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 T 2 mode of a (111) facet of the putative rock-salt structure.