Transient Structural Transition in Ovonic Threshold Switching Glass

Ovonic threshold switching (OTS), characterized by a rapid resistance drop in chalcogenide glass, has enabled the realization of memory and selectors. Despite over five decades of development, the challenges in characterizing the transient switching in amorphous materials upon reaching the threshold voltage have hindered the establishment of its underlying mechanism. This study uses femtosecond terahertz spectroscopy and ab initio simulation to elucidate the dynamics of the free‐carrier and IR‐active phonons involved in OTS. Specifically, in Te‐rich amorphous GeTe, the generation of transient phonons is observed within picoseconds, a phenomenon associated with an increased Born effective charge due to the alignment of Te‐centered bonds. The findings demonstrate a correlation between the enhancement of polarizability, due to orbital alignment during the disorder–order structural transition while maintaining a macroscopic amorphous structure, and the switching behavior. These results provide valuable insights into the enigmatic OTS phenomenon.