Quasi-two-dimensional electron gas at the interface of γ-Al<inf>2</inf>O<inf>3</inf>/SrTiO<inf>3</inf> 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

Research output: Contribution to journalArticle

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Abstract

We report the formation of a quasi-two-dimensional electron gas (2-DEG) at the interface of γ-Al<inf>2</inf>O<inf>3</inf>/TiO<inf>2</inf>-terminated SrTiO<inf>3</inf> (STO) grown by atomic layer deposition (ALD). The ALD growth of Al<inf>2</inf>O<inf>3</inf> 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 Al<inf>2</inf>O<inf>3</inf> films. As-deposited Al<inf>2</inf>O<inf>3</inf> films grown above 300 °C were crystalline with the γ-Al<inf>2</inf>O<inf>3</inf> phase. In situ x-ray photoelectron spectroscopy was used to characterize the Al<inf>2</inf>O<inf>3</inf>/STO interface, indicating that a Ti<sup>3+</sup> feature in the Ti 2p spectrum of STO was formed after 2-3 ALD cycles of Al<inf>2</inf>O<inf>3</inf> 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 cm<sup>2</sup> V<sup>-1</sup> s<sup>-1</sup> at room temperature and 15 K, respectively. The interfacial conductivity depended on the thickness of the Al<inf>2</inf>O<inf>3</inf> layer. The Ti<sup>3+</sup> 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

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atomic layer epitaxy
electron gas
high energy electrons
x ray spectroscopy
crystallinity
x ray diffraction
electron diffraction
photoelectron spectroscopy
conductivity
transmission electron microscopy
cycles
annealing
single crystals
room temperature
oxygen
water
temperature

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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Quasi-two-dimensional electron gas at the interface of γ-Al<inf>2</inf>O<inf>3</inf>/SrTiO<inf>3</inf> heterostructures grown by atomic layer deposition. / Ngo, Thong Q.; Goble, Nicholas J.; Posadas, Agham; Kormondy, Kristy J.; Lu, Sirong; McDaniel, Martin D.; Jordan-Sweet, Jean; Smith, David; Gao, Xuan P A; Demkov, Alexander A.; Ekerdt, John G.

In: Journal of Applied Physics, Vol. 118, No. 11, 115303, 21.09.2015.

Research output: Contribution to journalArticle

Ngo, TQ, Goble, NJ, Posadas, A, Kormondy, KJ, Lu, S, McDaniel, MD, Jordan-Sweet, J, Smith, D, Gao, XPA, Demkov, AA & Ekerdt, JG 2015, 'Quasi-two-dimensional electron gas at the interface of γ-Al<inf>2</inf>O<inf>3</inf>/SrTiO<inf>3</inf> heterostructures grown by atomic layer deposition', Journal of Applied Physics, vol. 118, no. 11, 115303. https://doi.org/10.1063/1.4930575
Ngo, Thong Q. ; Goble, Nicholas J. ; Posadas, Agham ; Kormondy, Kristy J. ; Lu, Sirong ; McDaniel, Martin D. ; Jordan-Sweet, Jean ; Smith, David ; Gao, Xuan P A ; Demkov, Alexander A. ; Ekerdt, John G. / Quasi-two-dimensional electron gas at the interface of γ-Al<inf>2</inf>O<inf>3</inf>/SrTiO<inf>3</inf> heterostructures grown by atomic layer deposition. In: Journal of Applied Physics. 2015 ; Vol. 118, No. 11.
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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.",
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AU - Posadas, Agham

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AU - Lu, Sirong

AU - McDaniel, Martin D.

AU - Jordan-Sweet, Jean

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AU - Demkov, Alexander A.

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N2 - 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.

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