Influence of stoichiometry on interfacial conductance in LaAlO$_3$/SrTiO$_3$ grown by 90$^o$ off-axis sputtering

TL;DR

This study investigates how varying the stoichiometry of LaAlO$_3$ during off-axis sputtering affects the interfacial conductance with SrTiO$_3$, revealing that cation ratio influences the transition from metallic to insulating interfaces.

Contribution

It demonstrates the critical role of La/Al stoichiometry controlled by growth pressure in determining the electrical properties of LaAlO$_3$/SrTiO$_3$ interfaces.

Findings

Higher growth pressure increases La/Al ratio and lattice constants.

Conductive interfaces become insulating at 0.10 mbar growth pressure.

Structural variations correlate with changes in interfacial conductance.

Abstract

We report on the fabrication of conducting interfaces between LaAlO$_3$ and SrTiO$_3$ by 90$^o$ off-axis sputtering in an Ar atmosphere. At a growth pressure of 0.04 mbar the interface is metallic, with a carrier density of the order of $10^{13}$ cm$^{-2}$ at 3 K. By increasing the growth pressure, we observe an increase of the out-of-plane lattice constants of the LaAlO$_3$ films while the in-plane lattice constants do not change. Also, the low-temperature sheet resistance increases with increasing growth pressure, leading to an insulating interface when the growth pressure reaches 0.10 mbar. We attribute the structural variations to an increase of the La/Al ratio, which also explains the transition from metallic behavior to insulating behavior of the interfaces. Our research emphasizes the key role of the cation stoichiometry of LaAlO$_3$ in the formation of the conducting interface, and also the control which is furnished by the Ar pressure in the growth process.