Relationship between resistive switching characteristics and band diagrams ofTi/Pr1−xCaxMnO3junctions

We investigated the Ca-composition dependence of the resistive switching (RS) characteristics and band diagrams in $\text{Ti}/{\text{Pr}}_{1\ensuremath{-}x}{\text{Ca}}_{x}{\text{MnO}}_{3}$ $[\text{PCMO}(x)]$ junctions and the impact of oxygen vacancies on the band diagrams. Hysteretic current-voltage characteristics, i.e., the RS effect, were observed for $\text{Ti}/\text{PCMO}(x)$ junctions with $x<0.8$, whereas junctions consisting of $n$-type semiconducting $\text{PCMO}(x)$ with $x>0.8$ showed almost no RS effect. The RS ratio ${R}_{\text{H}}/{R}_{\text{L}}$, where ${R}_{\text{H}}$ and ${R}_{\text{L}}$ are resistances of high- and low-resistance states, respectively, showed a clear $x$ dependence: ${R}_{\text{H}}/{R}_{\text{L}}$ increased with increasing $x$ and was maximized at $x\ensuremath{\sim}0.4$. Cross-sectional transmission electron microscope images of the switched $\text{Ti}/\text{PCMO}(x)$ junctions confirmed the formation of amorphous ${\text{TiO}}_{y}$ layers at the interfaces. Electron energy-loss measurements of the $\text{Mn-}L$ edge indicated that oxygen-deficient $\text{PCMO}(x)$ layers were formed at the interface due to the electrochemical migration of oxygen ions. Optical-absorption measurements of oxygen-deficient $\text{PCMO}(x)$ films revealed that the formation of oxygen vacancies increased the band gap of $\text{PCMO}(x)$. On the basis of the results, we propose a possible model involving the change in barrier height and/or width for the hole-carrier conduction at the $\text{PCMO}(x)$ interface induced by the electrochemical migration of oxygen vacancies as the mechanism of the RS effect.