Dynamics of Photogenerated Surface Charge on BiFeO₃ Films

We report on the spatial and temporal evolution of photoinduced charge generation and carrier separation in heteroepitaxial BiFeO(3) thin films deposited on Nb:SrTiO(3) as measured in ambient at room temperature with Kelvin probe and piezoresponse force microscopy. Contributions from the self-poled and ferroelectric polarization charge are identified from the time evolution of the correlated surface potential and ferroelectric polarization in films as grown and following poling, and at different stages and intensities of optical illumination. Variations in the surface potential with bias voltage, switching history, and illumination intensity indicate how both bulk ferroelectric photovoltaic and the domain wall offset potential mechanisms contribute to the photogenerated charge.