High Mobility inLaAlO3/SrTiO3Heterostructures: Origin, Dimensionality, and Perspectives

Abstract

We have investigated the dimensionality and origin of the magnetotransport properties of LaAlO3 films epitaxially grown on TiO2-terminated SrTiO3(001) substrates. High-mobility conduction is observed at low deposition oxygen pressures (P(O2)<10(-5) mbar) and has a three-dimensional character. However, at higher P(O2) the conduction is dramatically suppressed and nonmetallic behavior appears. Experimental data strongly support an interpretation of these properties based on the creation of oxygen vacancies in the SrTiO3 substrates during the growth of the LaAlO3 layer. When grown on SrTiO3 substrates at low P(O2), other oxides generate the same high mobility as LaAlO3 films. This opens interesting prospects for all-oxide electronics.

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

“…For this, we choose LAO grown on STO as it is a very p ox sensitive system. This system shows interface conduction, when the STO substrate is not reduced, and additional bulk conduction, when STO is reduced7162123. Thus LAO/STO has the advantage of a measurable sheet carrier concentration at room temperature even if the STO substrate is not reduced.…”

“…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.…”

“…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.…”