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

TL;DR

This study demonstrates the synthesis and detailed interfacial characterization of stable 2D electron gases in Si3N4/Al//KTaO3 heterostructures, revealing how Al layer thickness influences electronic properties through oxygen depletion effects.

Contribution

It provides new insights into the formation, stability, and tunability of 2DEGs in KTaO3-based heterostructures with detailed chemical and structural analysis.

Findings

Al layer fully oxidizes into AlOx, depleting oxygen from KTaO3

Thicker Al layers increase carrier density but decrease mobility

Oxygen depletion zone extends 3-5 nm into the substrate

Abstract

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 AlOx, 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.