Direct ab-initio molecular dynamic study of ultrafast phase change in Ag-alloyed Ge2Sb2Te5

摘要

We employed ab-initio molecular dynamics to directly simulate the effects of Ag alloying (less than 5% Ag concentration) on the phase change properties of Ge2Sb2Te5. 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 (sp3 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 Ag0.5Ge2Sb2Te5 is not less than that in Ge2Sb2Te5. Moreover, the smaller density difference and the larger energy difference between the two phases of Ag0.5Ge2Sb2Te5 (compared to Ge2Sb2Te5) suggest a smaller residual stress in devices due to phase transition and improved thermal stability for Ag0.5Ge2Sb2Te5. The potential viability of this material suggests the need for a wide exploration of alternative phase change memory materials.