Optical excitation-induced ultrafast amorphization in the Y-Sb-Te alloy system: Insights from real-time time-dependent DFT with molecular dynamics calculations

Abstract

In general, shortening the laser pulse width can suppress thermal dissipation to allow for sub-picosecond phase change during amorphization, yet there is no consistent evidence for the mechanistic exploration of its ultrafast dynamics at the atomic scale. Herein, a real-time time-dependent density-functional theory molecular dynamic (rt-TDDFT-MD) in a photoexcited fashion is applied to disclose an undetected effect of the experimentally observed Y-Sb-Te amorphization process at elevated temperature. Varying the optical excitation from $2%$ to $8%$ of valence electrons during the amorphization process can result in a variety of structures ranging from entire crystalline to amorphied shapes, satisfying the amorphous state at 1.2 ps upon $8%$ excitation. We conclude that the low concentration of photoexcitation fails to conquer the potential barrier height of Y-Sb-Te for fully facilitating amorphization. The $8%$ of photoinduced Te-$p$ electrons enhances the massive occupation of Y-$d{t}_{2g}$ orbitals and creates a flatter potential energy surface, which forces Y-centered motifs to perform $d{t}_{2g}\text{\ensuremath{-}}\phantom{\rule{4.pt}{0ex}}\text{and}\phantom{\rule{4.pt}{0ex}}{e}_{g}$-directed transition in the signature bond angle of the rock salt lattice. Thus it can rapidly dissociate the Sb-Te bond and facilitate the ultrafast formation of the amorphous phase. The incorporation of optical interventions drives the lattice to manifest disordered states, as well as allowing for accurate manipulation of the electronic structure to further reduce the time consumed in the amorphization process. The present works pave the way for the design of PCMs-based optoelectronic and microelectronic devices with comprehensive ultrafast response.