X‐Ray Photoelectron Spectroscopy Analysis of Ge–Se Chalcogenides

Ovonic threshold switch (OTS) is a promising selector technology for 3D high‐density memory applications, with Ge – Se alloys serving as a key material platform. While OTS behavior is believed to arise from electronic switching mechanisms, a full understanding of the underlying band structure and atomic structure across the entire Ge – Se compositional range remains incomplete—particularly in the Se‐rich ( x < 20 at%) and Ge‐dominant ( x > 50 at%) regimes. Here, the X ‐ ray photoelectron spectroscopy and valence band analysis is employed across the full Ge – Se compositional range (Ge x Se 1− x , x = 0 – 100 at%). Three structural regimes emerge: Se‐rich networks ( x < 40 at%) maintain 4:2 Ge:Se coordination, Ge‐rich regions ( x = 40 – 60 at%) show competing 3:3 Ge – Se and GeGe homopolar bonds, while the Ge‐dominant systems ( x ≥ 70 at%) exhibit >72% homopolar bonding. Valence band spectral fingerprints reveal Se ‐ chain disintegration and formation of different types of GeSe bonds as well as homopolar GeGe bonds. The results establish composition–structure relationships in chalcogenides, demonstrating that a controlled Ge incorporation optimizes the OTS performance through a defect‐mediated bond engineering.