Temperature dependent polaronic contribution on conduction mechanism in ceria-based devices

Abstract

The role of temperature dependent polaron density in current conduction mechanism of CeO2-based devices is investigated where CeO2−x films were deposited at different Ar:O2 ratios at room temperature using rf sputtering. I–V measurements on metal–oxide–semiconductor (MOS) devices at different temperatures show a three order current change in unipolar and bipolar switching having triggering voltages ranging from ±0.7 V at 80–100 °C to ∼±1.0 V at 150 and 200 °C and are reproducible in repeat cycles. Temperature dependent x-ray photoelectron spectroscopy (XPS) and grazing incidence x-ray diffraction (GIXRD) studies indicate along with stoichiometry dependent polaron contribution, the change in lattice parameters of polycrystalline CeO2 film also contributes to the resistive switching properties of CeO2-based devices with temperature. Oxygen vacancy movements in the form of hopping of polarons between the nearest neighbours and next to nearest neighbour sites as well facilitate the transitions at elevated temperatures. As predicted in the theoretical model, it is experimentally verified here that the conduction path created at elevated temperature vanishes at relatively higher temperatures due to too frequent polaron hopping. It is further observed that the density of polarons also increases with temperature that in turn hinders the switching behaviour of the devices at elevated temperatures.