Dipole pinning effect on photovoltaic characteristics of ferroelectric BiFeO_3 films

摘要

Ferroelectric bismuth ferrite is an attractive candidate for switchable devices. The effect of dipole pinning due to the oxygen vacancy layer on the switching behavior of the BiFeO_3 thin film fabricated by the chemical solution deposition method was studied after annealing under air, O_2, and N_2 environment. The air annealed film showed well defined and dense grains leading to a lower leakage current and superior electrical properties compared to the other two films. The photovoltage and transient photocurrent measured under positive and negative poling elucidated the switching nature of the films. Though the air and O_2 annealed films showed a switchable photovoltaic response, the response was severely affected by oxygen vacancies in the N_2 annealed film. In addition, the open circuit voltage was found to be mostly dependent on the polarization of BiFeCO_3 rather than the Schottky barriers at the interface. This work provides an important insight into the effect of dipole pinning caused by oxygen vacancies on the switchable photovoltaic effect of BiFeO_3 thin films along with the importance of stoichiometric, defect free, and phase pure samples to facilitate meaningful practical applications.