Switchable photovoltaic response in hexagonal LuMnO3 single crystals

Abstract

Hexagonal manganites, such as h-LuMnO3, are ferroelectric with its polar axis along the hexagonal axis and have a narrow electronic bandgap (≈ 1.5 eV). Using Pt electrodes, h-LuMnO3 single crystals display a strong rectification, characteristic of a Schottky diode, and a large photoresponse. It is found that the short circuit photocurrent Jsc along the polar axis is modulated (up to 25 %) by the direction of the ferroelectric polarization P, leading to a short circuit photocurrent loop that mimics the ferroelectric polarization, and by polarization backswitching. However, a non-switchable Jsc persists. Diffusion photocurrent is shown to dominate current-in-plane measurements and contributes to the non-switchable Jsc. This observation illustrates the dramatic role of the large optical absorption in hexagonal manganites. The accompanying optical dichroism shall challenge disentangling a genuine bulk photovoltaic response in h-LuMnO3 single crystal contributing to the non-switchable Jsc. Epitaxial thin films may offer a suitable alternative.

Bulk photovoltaic effect in hexagonal LuMnO3 single crystals

“…This difference is a signature of a switchable J drift,SW term, that at remanence and depending on the direction of ferroelectric polarization, affects the internal electric field in h-LMO and thus J sc . As already reported, polarizationmodulated Schottky barriers at h-LMO/electrode interfaces [24] allow us to modulate the photocurrent upon P switching. As observed, at remanence, J sc is modified by less than 10%, and thus the BPE coefficient extracted using Eqs.…”

“…The ferroelectric P(E ) loops of these crystals display a remanent room-temperature polarization of P r ≈ 7.3 μC/cm 2 and the reported I (V ) characteristics clearly indicate a photovoltaic response [24]. However, the conventional photoresponse and the bulk photovoltaic effect are intertwined, as shown in the following, and disentangling their relative contributions is challenging.…”

“…that give rise to a switchable J drift contribution (denoted here J drift,SW ) and a nonswitchable component respectively (denoted here J drift,NSW ) as discussed in Ref. [24]. The J drift,SW contribution can be evaluated by performing and comparing J sc measurements after prepolarizing the sample up or down.…”

“…with a duration of ≈ 50 s, which is long enough to saturate the polarization of the sample [P(E ) loops were measured at 1 kHz] [24]. After a dwell time τ d = 5 s, the short circuit photocurrent was recorded at various light polarization direction (ϕ) and incidence angle (θ ).…”

Bulk photovoltaic effect modulated by ferroelectric polarization back-switching

“…10,11 Discerning these different contributions to J sc (¼J BPE þ J E þ J D ), particularly J BPE and J E , requires knowing the ferroelectric polarization P state when J sc is measured. 12 This seemingly simple requirement, in practice, could be difficult to achieve. Indeed, the presence of E dep and E im may hinder, keeping the polarization at saturated state, 13,14 and at remanence, when J sc is measured, polarization back-switching may have occurred leading to a ferroelectric multidomain state or even reversing the overall polarization.…”