Origin of charge density at LaAlO3-on-SrTiO3 heterointerfacespossibility of intrinsic doping Page: 3 of 14
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important subsidiary question is whether experimental conditions can be identified for which the
intrinsic limit can be achieved.
The high sheet conductivities and carrier densities found by Ohtomo and Hwang have
been linked in preliminary arguments by us and by others to possible oxygen vacancies (i.e.,
extrinsic doping) in the SrTiO3 substrate. We further suggested that these vacancies are a result
of high energy particle bombardment during the Pulsed Laser Deposition (PLD) process [6, 7]
used so far by all workers in the field to make these hetero-structures. In addition, we proposed
that the high mobility results from the thermal distribution of electrons away from the interface
(consistent with Poisson's equation) where the intrinsic (dopant free) high mobility of SrTiO3 is
available. As we shall see, because of the very large dielectric constant of SrTiO3 at low
temperatures, this distribution can reach a large distance into the SrTiO3.
In this Letter, we present a much more thorough study of the nature and origins of this
conducting layer that puts our initial proposal on much firmer ground. We also show that
annealing these interfaces at elevated temperatures in oxygen leads to a greatly reduced carrier
density that is close in magnitude to that expected on simple ground from an ideal interface.
More explicitly, transport, in situ UPS, Near Edge X-ray Absorption Spectroscopy (NEXAS) and
visible to vacuum UV-Spectroscopic Ellipsometry (vis-VUV-SE) measurements have been
performed on samples prepared under different oxidation conditions. From these experiments it
is clear that, over a wide range of growth conditions, the large sheet charge density observed at
these hetero-interfaces is due almost certainly to oxygen vacancies (donating electrons) in the
All of the films reported here were grown using Pulsed Laser Deposition (PLD) as
described previously . During growth, Reflection High Energy Electron Diffraction (RHEED)
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Siemons, W. Origin of charge density at LaAlO3-on-SrTiO3 heterointerfacespossibility of intrinsic doping, article, April 29, 2010; United States. (digital.library.unt.edu/ark:/67531/metadc926390/m1/3/: accessed November 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.