Flexoelectric Thin-Film Photodetectors

Abstract

The flexoelectric effect, which manifests itself as a strain-gradient-induced electrical polarization, has triggered great interest due to its ubiquitous existence in crystalline materials without the limitation of lattice symmetry. Here, we propose a flexoelectric photodetector based on a thin-film heterostructure. This prototypical device is demonstrated by epitaxial LaFeO 3 thin films grown on LaAlO 3 substrates. A giant strain gradient of the order of 10 6 /m is achieved in LaFeO 3 thin films, giving rise to an obvious flexoelectric polarization and generating a significant photovoltaic effect in the LaFeO 3 -based heterostructures with nanosecond response under light illumination. This work not only demonstrates a novel self-powered photodetector different from the traditional interface-type structures, such as the p−n and Schottky junctions but also opens an avenue to design practical flexoelectric devices for nanoelectronics applications.

Significant Modulation of Ferroelectric Photovoltaic Behavior by a Giant Macroscopic Flexoelectric Effect Induced by Strain‐Relaxed Epitaxy

“…[16][17][18] Because the FEPV effect originates from the non-centrosymmetry, the centrosymmetry breaking and consequent polarization emergence (or change) caused by the strain gradient, a phenomenon known as flexoelectricity, can modulate the FEPV effect and even induce the PV effect in otherwise centrosymmetric materials. [19,20] Modulation of the FEPV effect by flexoelectricity is of particularly interest, because it can either enhance the PV outputs or modify the switchability of the FEPV effect. For example, Chu et al [21] observed a significant strain gradient-induced enhancement of photocurrent at the morphotropic phase boundaries (MPBs) in mixed-phase BiFeO 3 (BFO) films.…”

Lattice-mediated bulk flexoelectricity from first principles

“…mk,q and n (β) q (r) (together with the corresponding phonon counterparts) according to Eq. (15). The additional contribution originates from the second terms [∆ Ĥβ k,q , |∆u β mk,q and ∆n β q (r)] on the rhs of Eqs.…”

“…Notable examples include the mechanical manipulation of the ferroelectric polarization; 5,8,10 the flexoelectronic effect, where a flexoelectric voltage is used to gate transistor-like operations; 11,13,14 or the flexo-photovoltaic effect, whereby a strain-gradient increases by orders of magnitude the photocurrent generated in a photovoltaic device. 9,15 Future technologies based on flexoelectricity depend on maturing our understanding of the effect at the very fundamental level. The first-principles theory and calculations of flexoelectricity have made impressive progress in recent years, providing quantitatively predictive support to the interpretation of the experiments.…”

Lattice-mediated bulk flexoelectricity from first principles

“…Recent experimental work, either directly on nanomaterials [5][6][7] or by using the highly localized strain fields generated with a nanoscopic tip on a macroscopic surface [8][9][10][11][12], has demonstrated the great potential of flexoelectricity at the nanoscale. Notable examples include the mechanical manipulation of the ferroelectric polarization [5,8,10]; the flexoelectronic effect, where a flexoelectric voltage is used to gate transistorlike operations [11,13,14]; or the flexophotovoltaic effect, whereby a strain gradient increases by orders of magnitude the photocurrent generated in a photovoltaic device [9,15].…”