Nonlinear conductivity in SrTiO₃-based oxide heterostructures under strong electric fields

Ruslan Kalibek, Daria Sopyryaeva

2025

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DOI 10.54355/tbusphys/3.4.2025.0042
Data confidence 70 medium
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Abstract

This study explores the origin of nonlinear conductivity in epitaxial oxide heterostructures subjected to strong electric fields. We investigate vertical transport in Pt/SrTiO₃/Nb:SrTiO₃ and Pt/La₀.₇Sr₀.₃MnO₃/SrTiO₃/Nb:SrTiO₃ stacks with SrTiO₃ barrier thicknesses of 5, 10, and 20 nanometres. Heterostructures were grown by pulsed laser deposition and characterized structurally by X-ray diffraction, atomic force microscopy and cross-sectional transmission electron microscopy. Current–voltage measurements were performed over a wide voltage and temperature range, followed by model-based analysis to distinguish between Ohmic, space-charge-limited and trap-assisted conduction. Post-mortem electron microscopy was used to assess structural changes after strong-field stressing. All devices show a clear crossover from nearly linear conduction at low bias to a nonlinear regime at higher fields, with the threshold field increasing from about 110 kilovolts per centimetre for 5 nanometres to about 320 kilovolts per centimetre for 20 nanometres. Double-layer structures with La₀.₇Sr₀.₃MnO₃ exhibit systematically lower threshold fields (for example, about 140 kilovolts per centimetre for 10 nanometres) and stronger Poole–Frenkel-like response, indicating an enhanced role of interface-related trap states. Quantitative analysis of transformed current–voltage plots yields effective space-charge exponents between 1.6 and 2.1 and Poole–Frenkel slopes corresponding to activation energies of 50–120 millielectronvolts that decrease with increasing field. Electron microscopy confirms that the oxide remains structurally intact throughout the nonlinear regime and shows noticeable interface roughening only close to breakdown. These results demonstrate that nonlinear conduction in SrTiO₃-based heterostructures is governed by a field-induced crossover from bulk-limited, trap-assisted transport to increasingly interface-influenced conduction, and they define thickness and field windows where strong nonlinearity can be exploited without triggering irreversible structural damage.