Effect of oxygen vacancies in theSrTiO3substrate on the electrical properties of theLaAlO3∕SrTiO3interface

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

“…The reduction of STO in PLD vacuum chambers, however, is not only observed during deposition, but also observed when annealing at physical oxygen pressures below ≈7 · 10 −7  mbar163233, which is in contradiction to the thermodynamic equilibrium measurements performed in chemically controlled gas mixtures or with oxygen pumps232526. To our knowledge, no work sufficiently explained this contradiction between physical oxygen pressure and chemically controlled oxygen pressure so far.…”

“…At the same time some oxides require a low oxygen pressure during deposition in order to guarantee a low valence state of the involved cations1213, or to obtain layer-by-layer growth, as high physical pressures result in 3D growth101415. Thus when aiming for high quality heterostructures or superlattices the competition of crystalline perfection and stoichiometry limits the choice of materials and the achievable interface quality101617. An example for the importance of the oxygen pressure during growth is the LaAlO 3 (LAO)/STO heterostructure.…”

“…An example for the importance of the oxygen pressure during growth is the LaAlO 3 (LAO)/STO heterostructure. 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.…”

“…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.…”

“…Being able to explain the reduction of STO during annealing, we disentangle the reduction of STO during depositions. We do so using LAO growth on STO due to its oxygen pressure sensitivity7162123. We are able to separate influences induced by the plume from influences of an insufficient supply of oxygen and influences of the measurement devices.…”