On conditions leading to crossing of I–V curve in metal1|mixed-ionic–electronic-conductor|metal2 devices

• I–V relations and defects distributions in metal1|MIEC|metal2 devices are discussed.
• Crossing of I–V curves (at fixed temperature) is predicted for asymmetric devices.
• Asymmetries: in contact potential, material exchange or surroundings composition
• Crossing of I–V curves is predicted for asymmetric, periodic applied voltage, V.
• V asymmetries: in amplitudes for V > 0 and V < 0 or in scan rates for up and down V

Many experimental and some theoretical studies on two terminal devices in the form metal1|semiconductor|metal2 report on unusual I–V relations which exhibit hysteresis and crossing of the I–V curve under periodic applied voltage. It is believed that the semiconductors allow also for motion of ionic defects and they are thus, mixed-ionic–electronic-conductors (MIECs). The device simulated here is of the form metal1|MIEC|metal2 where the thin semiconductor layer is n-type and the donors are mobile. The applied voltage is periodic. It is limited so that the temperature is constant. The conduction electrons are coupled to the mobile donors via the Poisson equation thus the redistribution of donors under an applied voltage leads to dramatic changes in the device's resistance. The donors considered are native ones and the electrodes allow exchange of matter with the surroundings which affects the I–V relations. The results suggest that a necessary condition for I–V curve crossing is an asymmetry in the device or in the applied voltage.