Effect of Growth Induced (Non)Stoichiometry on Interfacial Conductance inLaAlO3/SrTiO3

Abstract

We demonstrate a link between the growth process, the stoichiometry of LaAlO(3), and the interfacial electrical properties of LaAlO(3)/SrTiO(3) heterointerfaces. Varying the relative La:Al cation stoichiometry by a few atomic percent in films grown at 1×10(-3) Torr results in a 2 and 7 order-of-magnitude change in the 300 and 2 K sheet resistance, respectively, with highly conducting states occurring only in La-deficient or Al-excess films. Further reducing the growth pressure results in an increase of the carrier density and a dramatic change in mobility. We discuss the relative contributions of intrinsic and extrinsic effects in controlling the physical properties of this widely studied system.

Unraveling the enhanced Oxygen Vacancy Formation in Complex Oxides during Annealing and Growth

“…The interface conductivity is usually described by a sheet carrier concentration n S , thus this quantity is further used instead of n . A n S of 1 · 10 14  cm −2 is usually expected for interface conduction181921, while a n S clearly above this value corresponds to contribution from the bulk conduction of the reduced STO substrate67.…”

“…While there is no change of the sheet carrier concentration, when the cold cathode gauge is applied (≈6.1 · 10 16  cm −2 ), post-annealing without an applied cold cathode gauge results in a decrease of the sheet carrier concentration (≈1.6 · 10 16  cm −2 ). This value, however, still corresponds to a contribution from the bulk conduction of the reduced STO substrate67.…”

“…The oxygen pressure applied during the deposition of metal oxides plays a key role for the properties of the resulting thin films567891011. For the deposition of fully oxygenated thin films, a high oxygen pressure is necessary to either compensate or inhibit the oxygen ejection from the thin film induced by the high energetic species of the plasma plume.…”

“…LAO/STO is well known for showing interface conductivity between two otherwise insulating materials716181920212223. However, if the STO substrate is reduced during low oxygen pressure deposition a strong contribution of the bulk conduction of the STO is measurable67, while a deposition at high oxygen pressures can result in an undesirably high resistance1820. One of the central challenges of PLD processes is thus, the need of a low oxygen pressure to grow certain complex oxides and the accompanied undesired reduction of the thin film, the substrate or both.…”

“…Numerous examples can be found in literature for the reduction of STO substrates during pulsed laser depositions for physical oxygen pressures below 10 −5  mbar6711161718202122. This opposes the results of chemically controlled reducing atmosphere annealing experiments (H 2 /Ar/O 2 mixtures), for which the sample is, in opposite to vacuum annealing, under a physical pressure of 1 bar.…”