Journal
JOURNAL OF APPLIED PHYSICS
Volume 118, Issue 11, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.4930575
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Funding
- Office of Naval Research [N00014-10-10489]
- Air Force Office of Scientific Research [FA9550-12-10494, FA9550-12-1-0441]
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-98CH10886]
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We report the formation of a quasi-two-dimensional electron gas (2-DEG) at the interface of gamma-Al2O3/TiO2-terminated SrTiO3 (STO) grown by atomic layer deposition (ALD). The ALD growth of Al2O3 on STO(001) single crystal substrates was performed at temperatures in the range of 200-345 degrees C. Trimethylaluminum and water were used as co-reactants. In situ reflection high energy electron diffraction, ex situ x-ray diffraction, and ex situ cross-sectional transmission electron microscopy were used to determine the crystallinity of the Al2O3 films. As-deposited Al2O3 films grown above 300 degrees C were crystalline with the gamma-Al2O3 phase. In situ x-ray photoelectron spectroscopy was used to characterize the Al2O3/STO interface, indicating that a Ti3+ feature in the Ti 2p spectrum of STO was formed after 2-3 ALD cycles of Al2O3 at 345 degrees C and even after the exposure to trimethylaluminum alone at 300 and 345 degrees C. The interface quasi-2-DEG is metallic and exhibits mobility values of similar to 4 and 3000 cm(2) V-1 s(-1) at room temperature and 15 K, respectively. The interfacial conductivity depended on the thickness of the Al2O3 layer. The Ti3+ signal originated from the near-interfacial region and vanished after annealing in an oxygen environment. (C) 2015 AIP Publishing LLC.
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