Effect of SrTiO3 oxygen vacancies on the conductivity of LaTiO3/SrTiO3 heterostructures

Bryce I. Edmondson, Shuhaog Liu, Sirong Lu, Hsin Wei Wu, Agham Posadas, David J. Smith, Xuan P.A. Gao, Alexander A. Demkov, John G. Ekerdt

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11 Scopus citations

Abstract

In this work, we report the formation of a conductive layer through oxygen vacancies in an underlying SrTiO3 (STO) layer due to the growth of LaTiO3 (LTO) and the resulting LTO thickness-dependent conductivity of the LTO/STO system. Crystalline LTO films were grown by molecular beam epitaxy on TiO2-terminated STO(001) single-crystal substrates and 8-unit-cell (u.c.) STO template layers grown on Ge(001), under partial pressures of molecular oxygen ranging from 10-10 to 10-7 Torr. Film crystallinity was studied by in situ reflection high-energy electron diffraction, ex situ X-ray diffraction, and ex situ transmission electron microscopy. Film composition and the existence of oxygen vacancies were confirmed by in situ X-ray photoelectron spectroscopy. LTO films grown on STO substrates at oxygen partial pressures of 10-10 Torr were optimally oxidized (1:1:3 La:Ti:O). However, LTO films grown on 8-u.c. templates of STO on Ge with oxygen partial pressures less than 10-7 Torr showed extensive reduction of the Ti oxide and desorption of Sr/SrO in the STO layer. LTO films began to over-oxidize when grown on STO single-crystal substrates at oxygen partial pressures greater than 10-10 Torr but were nearly optimally oxidized when grown on STO templates on Ge at oxygen partial pressures of 10-7 Torr. Electrical characterization showed a dependence of conductivity on the thickness of the LTO films, with sheet carrier densities reaching ∼5 × 1016 cm-2 for 20-u.c. (8-nm-thick) LTO/STO grown at 10-10 Torr of oxygen, suggesting that significant conduction occurred throughout the STO substrate due to the formation of oxygen vacancies.

Original languageEnglish (US)
Article number185303
JournalJournal of Applied Physics
Volume124
Issue number18
DOIs
StatePublished - Nov 14 2018

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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