Boosting Piezoelectricity Under Illumination via the Bulk Photovoltaic Effect and the Schottky Barrier Effect in BiFeO3.

Piezoelectricity is a key functionality induced by conversion between mechanical and electrical energy. Enhancement of piezoelectricity in ferroelectrics often has been realized by complicated synthetical approaches to host unique structural boundaries, so-called morphotropic phase boundaries. While structural approaches have been well-known, enhancing piezoelectricity by external stimuli has yet to be clearly explored despite their advantages of offering not only simple and in-situ control without any prior processing requirement, but compatibility with other functionalities. Here, we show that light is a powerful control parameter to enhance the piezoelectric property of a BiFeO3 single crystal. Our series of PFM and C-AFM based measurements under illumination reveal a locally enhanced effective piezoelectric coefficient, dzz , eventually showing almost a seven-fold increase. We explain this phenomenon with theoretical models by introducing the two main underlying mechanisms attributed to the bulk photovoltaic effect and Schottky barrier effect, involving the role of open circuit voltage and photocharge carrier density. These results provide key insights to light-induced piezoelectricity enhancement, offering its potential for multifunctional optoelectronic devices. This article is protected by copyright. All rights reserved.