Scavenging of oxygen vacancies at modulation-doped oxide interfaces: Evidence from oxygen isotope tracing

TL;DR

This study uses oxygen isotope tracing to demonstrate that redox reactions occur at oxide interfaces during 2DEG formation and that manganite buffer layers suppress oxygen exchange, leading to enhanced electron mobility.

Contribution

It provides direct evidence of oxygen exchange dynamics at oxide interfaces and shows how manganite buffers suppress these reactions to improve mobility.

Findings

Redox reactions occur at oxide interfaces even at room temperature.

Manganite buffer layers suppress oxygen exchange and carrier density.

Buffer layers enhance electron mobility by preventing substrate reduction.

Abstract

The introduction of manganite buffer layers, La7/8Sr1/8MnO3 (LSMO) in particular, at the metallic interface between SrTiO3 (STO) and another band insulator suppresses the carrier density of the interfacial two-dimensional electron gas (2DEG) and improves significantly the electron mobility. However, the mechanisms underlying the extreme mobility enhancement remain elusive. Herein, we used 18O isotope exchanged SrTi18O3 as substrates to create 2DEG at room temperature with and without the LSMO buffer layer. By mapping the oxygen profile across the interface between STO18 and disordered LaAlO3 or yttria-stabilized zirconia (YSZ), we provide unambiguous evidence that redox reactions occur at oxide interfaces even grown at room temperature. Moreover, the manganite buffer layer not only suppresses the carrier density but also strongly suppresses the oxygen exchange dynamics of the STO substrate, which likely prevents the reduction of STO during the formation of the 2DEG. The underlying mechanism on the enhanced electron mobility at buffered oxide interfaces is also discussed.