Untwining polar contributions from light-polarization dependent photovoltaic response of LuMnO3-based ferroelectric capacitors

Narrow bandgap ferroelectrics are receiving a renewed interest for photovoltaic applications aiming at exploiting new functionalities arising from bulk photovoltaic effect (BPE). We report on the photovoltaic response of vertical capacitors of ferroelectric hexagonal LuMnO3 films sandwiched between semitransparent top electrodes (Pt, Co, Ti) and a common bottom (Pt) bottom electrode. Our results show that the presence of electrodes, other than their optical transmittance, crucially determines the imprint in the ferroelectric layer and ultimately the sensitivity of short circuit current density (Jsc) to the ferroelectric polarization direction. The use of ultrathin (7 nm) Pt top electrodes allowed to obtain a large Jsc (up to 100 mA/cm2) and an open circuit voltage of Voc ≈ 0.52 V, with a responsivity of 2 × 10−3 A/W. Yet, polarization back-switching due to imprint largely washes out the dependence of Jsc on the direction of the polarization and thus, at first sight, Jsc seemingly appears to be ruled by conventional photovoltaic response. However, a pioneering analysis of the light-polarization dependent photosensitivity, allowed to disentangle for the first time, a genuine contribution of BPE from a ubiquitous Fresnel-like contribution arising from interfaced optical media.