Direct ab-initio molecular dynamic study of ultrafast phase change in Ag-alloyed Ge$_{2}$Sb$_{2}$Te$_{5}$

TL;DR

This study uses ab-initio molecular dynamics to investigate how 5% Ag alloying affects the phase change properties of Ge2Sb2Te5, revealing preserved short-range order, improved chemical order, and potential benefits for phase change memory applications.

Contribution

It provides the first ab-initio simulation analysis of Ag alloying effects on Ge2Sb2Te5's phase change behavior, highlighting improved thermal stability and reduced residual stress.

Findings

Crystallization speed remains high with Ag alloying.

Reduced density and energy differences suggest lower residual stress.

Enhanced thermal stability of Ag-alloyed phase change material.

Abstract

We employed ab-initio molecular dynamics to directly simulate the effects of Ag alloying ($\sim5%$ Ag concentration) on the phase change properties of Ge$_{2}$Sb$_{2}$Te$_{5}$. The short range order is preserved, whereas a slight improvement in the chemical order is observed. A slight decrease in the fraction of tetrahedral Ge (sp$^{3}$ bonding) is reflected in the reduction of the optical band gap and in the increased dielectric constant. Simulations of the amorphous to crystalline phase change cycle revealed the fact that the crystallization speed in Ag$_{0.5}$Ge$_{2}$Sb$_{2}$Te$_{5}$ is no less than that in Ge$_{2}$Sb$_{2}$Te$_{5}$. Moreover, the smaller density difference and the larger energy difference between the two phases of Ag$_{0.5}$Ge$_{2}$Sb$_{2}$Te$_{5}$ (compared to Ge$_{2}$Sb$_{2}$Te$_{5}$) suggest a smaller residual stress in devices due to phase transition and improved thermal stability for Ag$_{0.5}$Ge$_{2}$Sb$_{2}$Te$_{5}$. The potential viability of this material suggests the need for a wide exploration of alternative phase change memory materials.