Relationship between resistive switching characteristics and band diagrams of Ti/Pr1-xCaxMnO3 junctions

We investigated the Ca-composition dependence of the resistive switching (RS) characteristics and band diagrams in Ti/Pr1-xCaxMnO3 [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 Ti/PCMO(x) junctions with x < 0.8, whereas junctions consisting of n-type semiconducting PCMO(x) with x>0.8 showed almost no RS effect. The RS ratio R-H/R-L, where R-H and R-L are resistances of high- and low-resistance states, respectively, showed a clear x dependence: R-H/R-L increased with increasing x and was maximized at x similar to 0.4. Cross-sectional transmission electron microscope images of the switched Ti/PCMO(x) junctions confirmed the formation of amorphous TiOy layers at the interfaces. Electron energy-loss measurements of the Mn-L edge indicated that oxygen-deficient PCMO(x) layers were formed at the interface due to the electrochemical migration of oxygen ions. Optical-absorption measurements of oxygen-deficient PCMO(x) films revealed that the formation of oxygen vacancies increased the band gap of 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 PCMO(x) interface induced by the electrochemical migration of oxygen vacancies as the mechanism of the RS effect.