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Polaron-Induced Midgap States in Ovonic Threshold Switching Material for 3D Phase-Change Memory Applications.
Huan-Ran Ding1, Tian-Yu Zhao1, Nian-Ke Chen1
1State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 130012 Changchun, China.
The Journal of Physical Chemistry Letters
|February 13, 2026
Summary
Ovonic threshold switching (OTS) selectors are key for 3D memory. This study reveals excited carriers form polarons, creating midgap states that enable OTS switching, guiding future material design.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Computational Materials Science
Background:
- Ovonic threshold switching (OTS) selectors are critical for mitigating sneak-path currents in 3D-crossbar phase-change memory arrays.
- The precise origin and evolution of midgap (defect) states in OTS amorphous materials, vital for the switching mechanism, are not fully understood, leading to ongoing debates.
Purpose of the Study:
- To investigate the electron-hole-pair excitation mechanism during the switching-on process in representative OTS materials (GeSe, GeS, SiGeAsTe).
- To elucidate the formation of midgap states and their role in the Ovonic threshold switching behavior.
Main Methods:
- First-principles calculations were employed to simulate the excited-state dynamics and carrier interactions.
- Analysis focused on electron-phonon coupling, polaron formation, and the electronic structure modifications leading to midgap states.
Main Results:
- Excited electron-hole pairs induce polaron formation via strong electron-phonon coupling in GeSe, GeS, and SiGeAsTe.
- These polarons introduce midgap states, facilitating the switching-on process through a positive feedback mechanism.
- The observed polarons and midgap states are primarily associated with the conduction band, linked to metavalent or hyperbonding characteristics of these chalcogenide materials.
Conclusions:
- The study clarifies that excited states and polaron formation are key to generating midgap states in OTS materials.
- These findings provide crucial insights into the Ovonic threshold switching mechanism and offer guidance for developing enhanced OTS materials for advanced 3D phase-change memory applications.
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