Conducting interfaces between amorphous oxide layers and SrTiO3(110) and SrTiO3(111)

TL;DR

This study investigates the conduction properties of amorphous oxide interfaces with SrTiO3 substrates of different orientations, revealing that oxygen vacancy formation is primarily influenced by the oxygen affinity of the deposited metal ions rather than substrate orientation.

Contribution

It demonstrates that the critical thickness for conduction depends on the amorphous oxide composition and shows that oxygen vacancy formation is driven by metal ion oxygen affinity, not substrate orientation.

Findings

Critical thickness varies with amorphous oxide composition.

Oxygen vacancies are more abundant in amorphous interfaces.

Vacancy formation is linked to metal ion oxygen affinity.

Abstract

Interfaces between (110) and (111)SrTiO3 (STO) single crystalline substrates and amorphous oxide layers, LaAlO3 (a-LAO), Y:ZrO2 (a-YSZ), and SrTiO3 (a-STO) become conducting above a critical thickness tc. Here we show that tc for a-LAO is not depending on the substrate orientation, i.e. tc (a-LAO/(110)STO) ~ tc(a-LAO/(111)STO) interfaces, whereas it strongly depends on the composition of the amorphous oxide: tc(a-LAO/(110)STO) < tc(a-YSZ/(110)STO) < tc(a-STO/(110)STO). It is concluded that the formation of oxygen vacancies in amorphous-type interfaces is mainly determined by the oxygen affinity of the deposited metal ions, rather than orientational-dependent enthalpy vacancy formation and diffusion. Scanning transmission microscopy characterization of amorphous and crystalline LAO/STO(110) interfaces shows much higher amount of oxygen vacancies in the former, providing experimental evidence of the distinct mechanism of conduction in these interfaces.