Domain and Switching Control of the Bulk Photovoltaic Effect in Epitaxial BiFeO3 Thin Films

Abstract

Absence of inversion symmetry is the underlying origin of ferroelectricity, piezoelectricity, and the bulk photovoltaic (BPV) effect, as a result of which they are inextricably linked. However, till now, only the piezoelectric effects (inverse) have been commonly utilized for probing ferroelectric characteristics such as domain arrangements and resultant polarization orientation. The bulk photovoltaic effect, despite sharing same relation with the symmetry as piezoelectricity, has been mostly perceived as an outcome of ferroelectricity and not as a possible analytical method. In this work, we investigate the development of BPV characteristics, i.e. amplitude and angular dependency of short-circuit current, as the ferroelastic domain arrangement is varied by applying electric fields in planar devices of BiFeO3 films. A rather sensitive co-dependency was observed from measurements on sample with ordered and disordered domain arrangements. Analysis of the photovoltaic response manifested in a mathematical model to estimate the proportion of switched and un-switched regions. The results unravel the potential utility of BPV effect to trace the orientation of the polarization vectors (direction and amplitude) in areas much larger than that can be accommodated in probe-based techniques.

Anomalous circular bulk photovoltaic effect in BiFeO3 thin films with stripe-domain pattern

“…The measured values of the photovoltaic current (density) in y-direction are largely similar to the previously reported values 1 , 2 . The dependency on the light orientation θ match qualitatively the predicted sinusoidal response in Eq.…”

“…The re-discovery photovoltaic effect in ferroelectrics has far reaching implications that have been till now demonstrated. The obvious ones include the realization of junction free-photovoltaic modules 1 , and tracing polarization components, both in-plane 2 and out-of-plane 3 , via non-destructive methodologies. Generation of above bandgap open-circuit voltage ( V oc ) under suitable illumination is another outcome which has garnered immense attention 1 , 4 .…”

Bulk-Controlled Photovoltaic Effect in Nanometer-Thick Ferroelectric Pb(Zr0.2Ti0.8)O3 Thin Films and the Role of Domain Walls

“…The investigations conducted with thin film systems have attempted to realize similar scenarios by the use of planar electrodes, which are arranged tens of micrometers apart. 4,5 Although, the arrangement is certainly nonideal with inhomogeneous field distribution 19 sandwiching the material in-between the electrodes, that is, out-of-plane geometry. However, the inability to achieve a large thickness in thin films without the nucleation of dislocations, defects, and domain walls, 20,21 which can have a shunt-like character at room temperature, largely hampers the chances to focus on the BPV effect.…”

“…The generation of PV current without the prerequisite of a junction, as needed in a conventional solar cell, is indeed enticing and the related origin has been a subject of deliberation. The resulting PV effect is often referred to as the bulk photovoltaic (BPV) effect because the measured short-circuit current ( J SC ) and open-circuit voltage ( V OC ) are mostly determined by the overall conductivity of the material in between the electrodes, that is, the bulk of the sample is essential rather than just a junction. , While the manifestation of the BPV effect has been investigated and demonstrated in different ferroelectrics such as BiFeO 3 , − BaTiO 3 , − PbTiO 3 , , and KNbO 3 -based compounds, − the contributions from the unavoidable junction between the ferroelectric material and the electrodes cannot be neglected. − In this regard, the ferroelectric material has been assumed as a wide-band gap semiconductor, which in contact with a metallic electrode results in the formation of a Schottky junction at the interface. The built-in field within the interface is fully capable of keeping away the photo-generated charge carriers from recombination and thus resulting in a net PV current.…”

“…On the contrary, studies encompassing the BPV effect are mostly focused on the use of bulk samples in the form of single crystals predominantly in the monodomain state ,, The resulting large distance between the electrodes apparently allows highlighting the photocurrent generation within the bulk and minimize the contribution arising from junctions. The investigations conducted with thin film systems have attempted to realize similar scenarios by the use of planar electrodes, which are arranged tens of micrometers apart. , Although, the arrangement is certainly nonideal with inhomogeneous field distribution and nonuniform illumination. A more efficient measurement geometry will be sandwiching the material in-between the electrodes, that is, out-of-plane geometry.…”