Finite-size versus interface-proximity effects in thin-film epitaxial $SrTiO_3$

De Souza, R. A.; Dittmann, R.; Gunkel, F.; Hoffmann-Eifert, S.

doi:10.1103/PhysRevB.89.241401

Journal Article

FZJ-2014-04651

Finite-size versus interface-proximity effects in thin-film epitaxial $SrTiO_3$

De Souza, R. A. (Corresponding Author) ; Gunkel, F.FZJ* ; Hoffmann-Eifert, S.FZJ* ; Dittmann, R.FZJ*

2014
APS College Park, Md.

Physical review / B 89(24), 241401 (2014) [10.1103/PhysRevB.89.241401]

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Please use a persistent id in citations: http://hdl.handle.net/2128/9120 doi:10.1103/PhysRevB.89.241401

Abstract: The equilibrium electrical conductivity of epitaxial SrTiO3 (STO) thin films was investigated as a function of temperature, 950≤ T/K ≤1100, and oxygen partial pressure, 10−23≤ pO2/bar ≤1. Compared with single-crystal STO, nanoscale thin-film STO exhibited with decreasing film thickness an increasingly enhanced electronic conductivity under highly reducing conditions, with a corresponding decrease in the activation enthalpy of conduction. This implies substantial modification of STO's point-defect thermodynamics for nanoscale film thicknesses. We argue, however, against such a finite-size effect and for an interface-proximity effect. Indeed, assuming trapping of oxygen vacancies at the STO surface and concomitant depletion of oxygen vacancies—and accumulation of electrons—in an equilibrium surface space-charge layer, we are able to predict quantitatively the conductivity as a function of temperature, oxygen partial pressure, and film thickness. Particularly complex behavior is predicted for ultrathin films that are consumed entirely by space charge.

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