Giant bulk photovoltaic effect in thin ferroelectric ${\mathrm{BaTiO}}_3$ films

The voltage generated in a noncentrosymmetric crystal due to the bulk photovoltaic effect (BPE) can greatly exceed the energy gap, however, the light energy conversion efficiency is extremely low. Here we show that the BPE is remarkably enhanced in the case of thin films. The measurements of the BPE in heteroepitaxial single domain ferroelectric ${\mathrm{BaTiO}}_3$ thin films reveal the enhancement of both photoinduced electric field and conversion efficiencies of the BPE by more than 4 orders of magnitude. Besides the fundamental aspect, our results indicate the potential for the use of the BPE in photovoltaic applications.

Figure 1

(a) Isotropic and (b) anisotropic nonequilibrium carriers momentum distribution in centrosymmetric and noncentrosymmetric crystals corresponding to the classical and bulk photovoltaic effects, respectively.

Figure 2

Scheme of measurements of the bulk photovoltaic effect in thin-film ferroelectric ${\mathrm{BaTiO}}_3$ films (inset: optical microscopy view of the sample under investigation).

Figure 3

Time evolution of the photovoltaic current generated in a thin ferroelectric ${\mathrm{BaTiO}}_3$ film.

Figure 4

Photovoltaic current for different light intensities measured on a thin-film heteroepitaxial $\mathrm{Pt}/{\mathrm{BaTiO}}_3/\mathrm{Pt}$ sample for (a) $l=50$ nm and (b) $l=20$ nm: 1: dark current; 2: $I=1.5\times {10}^{-1}\mathrm{W}/{\mathrm{cm}}^2$; 3: $I=3\times {10}^{-1}\mathrm{W}/{\mathrm{cm}}^2$; 4: $I=4.5\times {10}^{-1}\mathrm{W}/{\mathrm{cm}}^2$; and 5: $I=7.5\times {10}^{-1}\mathrm{W}/{\mathrm{cm}}^2$.