Correlating the low-temperature photoluminescence with electron transport properties in cerium oxide thin film

Abstract

The complex interaction between the intrinsic and extrinsic state variables of strongly correlated insulator thin films is drawing interest as it shows memristive behavior that may be applicable to neuromorphic computing. Cerium oxide is an interesting material as its band structure is modified due to the formation of oxygen vacancy defects. The polaron formation that results from the reduction of the Ce4+ state to the Ce3+ state through oxygen vacancies is crucial for the electron transport in cerium oxide and is strongly influenced by temperature. In this work, we examined the relationship between the change in band structure and the associated conductivity at lower temperatures when ceria is exposed to light. Following light excitation, the creation of oxygen vacancies results in electron localization in the Ce 4f state, followed by the electron transition from 4f1 to 4f0, generating the PL spectra. With decreasing temperature, the lattice vibration decreases, and the splitting in the PL peak at a particular energy state validates the weaker electron–phonon interaction with an exciton trap. This reduces the carrier mobility of the film as observed from the resistance vs temperature curve of ceria under dark conditions. When excited by a particular energy of light, the electrons move more easily from the defect state to the conduction band, increasing conductivity at much lower temperatures than the conductivity under dark conditions.