Resistive switching suppression in metal/Nb:SrTiO$_3$ Schottky contacts prepared by room-temperature Pulsed Laser Deposition

Deepening the understanding of interface-type Resistive Switching (RS) in metal/oxide heterojunctions is a key step for the development of high-performance memristors and Schottky rectifiers. In this study, we address the role of metallization technique by fabricating prototypical metal/Nb-doped SrTiO$_3$ (M/NSTO) Schottky contacts via Pulsed Laser Deposition (PLD). Ultrathin Pt and Au electrodes are deposited by PLD onto single-crystal (001)-terminated NSTO substrates and interfacial transport is characterized by conventional macroscale methods and nanoscale Ballistic Electron Emission Microscopy. We show that PLD metallization gives Schottky contacts with highly reversible current-voltage characteristics under cyclic polarization. Room-temperature transport is governed by thermionic emission with Schottky barrier height $\phi_B$(Pt/NSTO)=0.71-0.75eV, $\phi_B$(Au/NSTO)=0.70-0.83eV and ideality factors as small as n(Pt/NSTO)=1.1 and n(Au/NSTO)=1.6. RS remains almost completely suppressed upon imposing broad variations of the Nb doping and of the external stimuli (polarization bias, working temperature, ambient air exposure). At the nanoscale, we find that both systems display high spatial homogeneity of $\phi_B$(<50meV), which is only partially affected by the NSTO mixed termination (|$\phi_B$ (M/SrO) - $\phi_B$ (M/TiO$_2$)|<35meV). Experimental evidences and theoretical arguments indicate that the PLD metallization mitigates interfacial layer effects responsible for RS. This occurs thanks either to a reduction of the interfacial layer thickness and to the creation of an effective barrier against the permeation of ambient gas species affecting charge trapping and redox reactions. This description allows to rationalize interfacial aging effects, observed upon several-months-exposure to ambient air, in terms of interfacial re-oxidation.
Comment: 31 pages, 7 figures