Ovonic Threshold Switching Induced by Reversal of Peierls-Like Distortion in GeSe₂ Glass

The ovonic threshold switching (OTS) effect, observed in chalcogenide glasses (CGs), involves a reversible transition from a high-resistive state (OFF state) to a conductive state (ON state) under an electric field. However, direct observation of the dynamic process of the OTS effect is challenging, leading to debate about the mechanism of the OTS effect. In this work, the OTS effect in GeSe₂ glass is studied using ab initio molecular dynamics (AIMD) with electric fields. Before applying an electric field, the glass is in the OFF state. After applying electric fields of different strength, mid-gap states appear and band tail states get wider. Atomic chains composed of Se atoms and a small number of Ge atoms, which contribute to some mid-gap states, are formed by reversal of Peierls-like distortion. These atomic chains result in chain-like molecular orbitals. The percolation of the metastable channel through a reversal of the Peierls-like distortion process on the atomic chains can be considered the cause of the transition to the ON state in GeSe₂ glass. Upon removing the electric field, the glass returns to the OFF state. This study provides insight into the conduction mechanism of CGs.