Quasi-two-dimensional electron gas at the interface of γ-Al2O3/SrTiO3 heterostructures grown by atomic layer deposition

Thong Q. Ngo, Nicholas J. Goble, Agham Posadas, Kristy J. Kormondy, Sirong Lu, Martin D. McDaniel, Jean Jordan-Sweet, David Smith, Xuan P A Gao, Alexander A. Demkov, John G. Ekerdt

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Abstract

We report the formation of a quasi-two-dimensional electron gas (2-DEG) at the interface of γ-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 °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 °C were crystalline with the γ-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 °C and even after the exposure to trimethylaluminum alone at 300 and 345 °C. The interface quasi-2-DEG is metallic and exhibits mobility values of ∼4 and 3000 cm2 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.

Original languageEnglish (US)
Article number115303
JournalJournal of Applied Physics
Volume118
Issue number11
DOIs
StatePublished - Sep 21 2015

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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    Ngo, T. Q., Goble, N. J., Posadas, A., Kormondy, K. J., Lu, S., McDaniel, M. D., Jordan-Sweet, J., Smith, D., Gao, X. P. A., Demkov, A. A., & Ekerdt, J. G. (2015). Quasi-two-dimensional electron gas at the interface of γ-Al2O3/SrTiO3 heterostructures grown by atomic layer deposition. Journal of Applied Physics, 118(11), [115303]. https://doi.org/10.1063/1.4930575