Resistive switching induced by charge trapping/detrapping: a unified mechanism for colossal electroresistance in certain Nb:SrTiO3-based heterojunctions

SrTiO3 remains at the core of research on oxide electronics, owing to its fascinating properties and wide applications as a commercial substrate. Heterojunctions based on Nb-doped SrTiO3 (NSTO), including both metal/NSTO Schottky junctions (MSJs) and NSTO-based ferroelectric tunnel junctions (FTJs) have received considerable attention due to the colossal electroresistance (CER) effect. However, the mechanism underpinning the CER effect is still poorly understood. Here, we conduct a comparative study on the CER effects in Au/NSTO MSJs and Au/BaTiO3/NSTO FTJs. The two types of heterojunctions show many similarities in resistive switching characteristics, including hysteretic current-voltage curves with asymmetric shapes, absence of critical switching fields, switching times on the scale of similar to 1.0 mu s, and resistance relaxations of the Curie-von Schweidler type. These results suggest that the CER effects in the MSJs and FTJs may have a common origin, i.e., charge trapping/detrapping, as further revealed by scanning Kelvin probe microscopy. Using temperature-dependent current-voltage, capacitance-voltage, and photo-response measurements, we demonstrate that charge trapping/detrapping could modify both the Schottky barrier profile and the tunneling process, and in turn lead to different transport mechanisms in different voltage regimes. The charge trapping/detrapping-induced CER effect can be well described by a metal-insulator-semiconductor (MIS) model, which reproduces the hysteretic current-voltage curves fairly well over a large range of voltage sweeping and thus provides a unified framework for the CER effects in certain NSTO-based heterojunctions.