Modulation of phase change characteristics in Ag-incorporated Ge2Sb2Te5 owing to changes in structural distortion and bond strength

Abstract

Ag-Incorporated Ge₂Sb₂Te₅ (AGST) crystallizes faster and at a lower temperature than Ge₂Sb₂Te₅ (GST). Many researchers have reported that these improvements could be attributed to a minute structural change because of the incorporated Ag. In a detailed study, we investigated this small structural change and its relationship with the phase change characteristics. Using various structural measurement methods and chemical bonding measurement tools, we confirmed the fine structural change, electron density distribution, and bond strength in GST thin films incorporated with 0%, 1%, and 10% Ag. From the experimental results, we identified that as the amount of incorporated Ag increases, the Ge–Te short bond length decreases and a homo-polar Ge–Ge bond is induced. When Ag is incorporated into the Ge site, the nearest neighbor bond strength between Ge and Te becomes much weaker. At the atomic level, the incorporated Ag induces one strong bond with the nearest Te, while the other bonds with Te are weakened. Therefore, the change in bond strength modulates the bond length between Ge and Te. Specifically, the Ge–Te short bond becomes shorter, and the long bond becomes relatively longer. This structural change indicates that the AGST has stronger Peierls distortion characteristics than GST. Finally, the modulated Peierls distortion changes the phase transition characteristics, such as the increase in the transition speed and the decrease in the phase change temperature.