Controlling the interfacial conductance in LaAlO3/SrTiO3 in 90∘ off-axis sputter deposition

Abstract

We report on the fabrication of conducting interfaces between ${\mathrm{LaAlO}}_{3}$ and ${\mathrm{SrTiO}}_{3}$ by ${90}^{\ensuremath{\circ}}$ 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 $1\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ at 3 K. By increasing the growth pressure, we observe an increase of the out-of-plane lattice constants of the ${\mathrm{LaAlO}}_{3}$ 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 shows that the control which is furnished by the Ar pressure makes sputtering as versatile a process as pulsed laser deposition, and emphasizes the key role of the cation stoichiometry of ${\mathrm{LaAlO}}_{3}$ in the formation of the conducting interface.