Evidence of bulk photovoltaic effect and large tensor coefficient in ferroelectric BiFeO 3 thin films

We present a study on the bulk photovoltaic effect (BPVE) in ferroelectric thin films, in which the photocurrent is measured with symmetric electrodes in the plane perpendicular to the ferroelectric polarization to eliminate the effect of the depolarization field and interfacial energy barriers. We show evidence of a strong BPVE in epitaxial BiFeO${}_{3}$ (BFO) films as thin as 40 nm. By taking into account the nonuniform absorption of incident photons, we obtain the bulk photovoltaic tensor coefficient ${\ensuremath{\beta}}_{22}$ for BFO thin films. Remarkably, it is about five orders of magnitude larger than that of other typical ferroelectric materials for visible wavelengths. The results indicate that the BPVE in ferroelectric BFO thin films could be further explored for solar light photovoltaic applications.