Unravelling the role of oxygen vacancies on the current transport mechanisms in all-perovskite nickelate/titanate heterojunctions for nonvolatile memory applications

The micrometer-sized nickelate-titanate heterojunctions with LaNiO3 (LNO) electrode have been fabricated to investigate the dominant current transport mechanisms under positive and negative bias. The LNO/SmNiO3 (SNO)/Nb:SrTiO3 (NSTO) heterojunction exhibits a highly rectifying feature with a very low leakage in a broad temperature region (from 200 to 425 K), which is attributed to the formation of a Schottky-like barrier at the SNO/NSTO interface. In addition, it is found that the trap defects (i.e., oxygen vacancies) play an essential role in determining the current density (J)-voltage (V) characteristics irrespective of the voltage polarity. The leakage current at low electric fields (<0.25 MV/cm) is dominated by temperature-enhanced trap assisted tunneling process, which is caused by the interface oxygen vacancy induced states. Further analysis suggests that, at high fields (>1.2 MV/cm), the leakage is ascribed to the bulk-limited field enhanced thermal ionization of trapped carriers in the SNO film (i.e., Poole-Frenkel emission). Specially, the oxygen vacancy redistribution near the SNO/NSTO heterointerface driven by a high temperature (425 K) or high electrical field (>3.8 MV/cm) stress is emphasized to account for the transition from the Schottky contact limited to bulk-limited conduction mechanism (i.e., space charge limited conduction). This work will benefit the further analysis of the resistive switching phenomena in nickelate-based devices, showing a potential for nonvolatile memory applications.