Sub‐Picosecond Non‐Equilibrium States in the Amorphous Phase of GeTe Phase‐Change Material Thin Films
Paloma Martinez, Valérie Blanchet, D. Descamps, Jean‐Baptiste Dory, C. Fourment, Irène Papagiannouli, S. Petit, Jean‐Yves Raty, Pierre Noé, J. Gaudin
Abstract
The sub-picosecond response of amorphous germanium telluride thin film to a femtosecond laser excitation is investigated using frequency-domain interferometry and ab initio molecular dynamics. The time-resolved measurement of the surface dynamics reveals a shrinkage of the film with a dielectric properties' response faster than 300 fs. The systematic ab initio molecular dynamics simulations in non-equilibrium conditions allow the atomic configurations to be retrieved for ionic temperature from 300 to 1100 K and width of the electron distribution from 0.001 to 1.0 eV. Local order of the structures is characterized by in-depth analysis of the angle distribution, phonon modes, and pair distribution function, which evidence a transition toward a new amorphous electronic excited state close in bonding/structure to the liquid state. The results shed a new light on the optically highly excited states in chalcogenide materials involved in both important processes: phase-change materials in memory devices and ovonic threshold switching phenomenon induced by a static field.