Origin of interfacial conductivity at complex oxide heterointerfaces: possibility of electron transfer from water chemistry at surface oxygen vacancies

TL;DR

This study investigates the interfacial conductivity in various complex oxide heterointerfaces, revealing that water chemistry at surface oxygen vacancies universally influences electron transfer and conductivity tuning.

Contribution

It proposes that water chemistry at surface oxygen vacancies is a common mechanism governing interfacial conductivity across different oxide heterointerfaces.

Findings

Conductivity depends on annealing conditions.

Surface treatment with water universally tunes conductivity.

Water chemistry at oxygen vacancies supplies electrons.

Abstract

Variety of conducting heterointerfaces have been made between SrTiO3 substrates and thin capping layers of distinctly different oxide materials that can be classified into polar band insulators (e.g. LaAlO3), polar Mott insulators (e.g. LaTiO3), apparently non-polar band insulators (e.g. {\gamma}-Al2O3), and amorphous oxides (e.g. amorphous SrTiO3). A fundamental question to ask is if there is a common mechanism that governs interfacial conductivity in all these heterointerfaces. Here, we examined the conductivity of different kinds of heterointerfaces by annealing in oxygen and surface treatment with water. It was found that the conductivity of all the heterointerfaces show a strong dependence on annealing, and can be universally tuned by surface treatment whose effect is determined by the annealing condition. These observations, together with ambient-pressure X-ray photoelectron spectroscopy measurements, suggest that water chemistry at surface oxygen vacancies is a common mechanism that supplies electrons to the interface.