Abstract
Phase change random access memory devices have evolved dramatically with the recent development of superlattice structure of Ge-Sb-Te material (GST-SL) in terms of its low power consumption. The phase change in GST-SL is mainly characterized by the displacement of Ge atoms. Here we examine a new phase change method, that is the manipulation of Ge-Te bonds using linearly-polarized femtosecond near-infrared optical pulses. As a result, we found that the p -polarized pump pulse is more effective in inducing the reversible and irreversible displacement of Ge atoms along [111] direction in the local structure. This structural change would be induced by the anisotropic carrier-phonon interaction along the [111] direction created by the p -polarized pulse.
Highlights
Optical manipulation of crystal structure is widely investigated in various kinds of materials
We found that the p-polarized pump pulse is more effective in inducing the reversible and irreversible displacement of Ge atoms along [111] direction in the local structure
We demonstrate ultrafast manipulation of atomic motion in GeTe/Sb2Te3 superlattice (GST-SL) [1] with rotating the polarization angle of a linearly-polarized femtosecond near-infrared optical pulse with the relatively lower fluence up to 78 μJ/cm2 and discuss about the driving force of the structural change
Summary
Optical manipulation of crystal structure is widely investigated in various kinds of materials. In GST-SL, reflectivity and conductivity changes are caused by displacement and coordination change of Ge atoms between tetrahedral position (reset-state) and octahedral position (set-state) [2, 3] followed by formation or dissolution of resonant bonding [4] From this point of view, selective excitation of specific bonding of Ge atoms can affect the dynamics of structural change. In order to realize the selective excitation, we observed ultrafast coherent atomic vibrational motion of Ge atoms employing coherent phonon spectroscopy as a function of the polarization angles of the pump pulse
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