High stability 2D electron gases formed in Si₃N₄/Al//KTaO₃ -(110) heterostructures: synthesis and in-depth interfacial characterization

The two-dimensional electron gas (2DEG) found in KTaO₃-based interfaces has garnered attention due to its remarkable electronic properties. In this study, we investigated the conducting system embedded at the Si₃N₄/Al//KTO(110) heterostructure. We demonstrate that the Al/KTO interface supports a conducting system, with the Si₃N₄ passivation layer acting as a barrier to oxygen diffusion, enabling ex-situ characterization. Our findings reveal that the mobility and carrier density of the system can be tuned by varying the Al layer thickness. Using scanning transmission electron microscopy, electron energy-loss spectroscopy, X-ray photoemission spectroscopy, and time-of-flight secondary ion mass spectrometry, we characterized the structural and chemical composition of the interface. We found that the Al layer fully oxidizes into AlO_x, drawing oxygen from the KTaO₃ substrate. The oxygen depletion zone extends 3–5 nm into the substrate and correlates to the Al thickness. Heterostructures with thicker Al layers exhibit higher carrier densities but lower mobilities, likely due to interactions with the oxygen vacancies that act as scattering centers. These findings highlight the importance of considering the effect and extent of the oxygen depletion zone when designing and modeling two-dimensional electron systems in complex oxides.