Origin of charge density at LaAlO3-on-SrTiO3 heterointerfacespossibility of intrinsic doping Page: 4 of 14
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was used both to determine the amount of material deposited and to monitor the morphology of
the samples. RHEED intensity oscillations reveal that typically 120 laser pulses are required to
grow a monolayer of LaAlO3. We found that if atomic oxygen is introduced during deposition,
the growth proceeds in a multilayer fashion, as revealed by the damping of the RHEED
oscillations, and thus could complicate the transport properties. Therefore, in order to achieve
high degrees of oxidation without such degradation, atomic oxygen was only introduced after
deposition during sample cooling, or after taking the sample out of the system for
characterization and subsequently reintroducing it for a post oxidation treatment.
After deposition, the samples were moved in situ into an adjacent photoemission analysis
chamber (<5x10-10 Torr base pressure) where their electronic structure was studied. Electrical
transport properties were measured ex situ with a Quantum Design Physical Properties
Measurement System (PPMS) using the Van der Pauw geometry, taking appropriate precautions
to avoid photo-induced carriers. NEXAS and vis-VUV-SE are described elsewhere [g' 9j
In Table 1, we first summarize the results of transport measurements on two classes of
samples. The first was prepared under relatively low oxidation conditions (10-6 Torr, as
measured with a hot cathode ion gauge), resulting in a high number of carriers . The second
was deposited and cooled at higher oxidation conditions (2x10-5 Torr), resulting in a reduced
carrier density. Within each class, samples with LaAlO3 thicknesses of 1 and 5ML were studied,
the thinner samples being used for surface sensitive measurements. The transport data are very
much in line with what has been reported by us and others, and demonstrate directly that the
oxygen pressure during deposition clearly affects the transport properties of these hetero-
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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/m1/4/: accessed July 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.