Single ferroelectric-domain photovoltaic switch based on lateral BiFeO3 cells

Abstract

The bistability of ferroelectric polarization states serves as a basis for solid-state memory. This phenomenon can also yield an interesting photovoltaic effect in such a way that the directional photocarrier motion follows the inherent potential gradient imposed by the ferroelectric polarization vectors. Here, we demonstrate a single-domain photovoltaic switch based on lateral BiFeO3 channels, in which such photovoltaic switching is achieved by a coherent single-domain reversal with a short electrical pulse. We then provide visual evidence for such operations with a series of spatially and spectrally resolved short-circuit photocurrent images. Specifically, we reveal that the sequential photovoltaic current images directly reflect the remanent polarization states of a single-domain channel. We also verify that, in multidomain channels, diffusive switching characteristics are determined not only by the internal polarization vector within the domain but also by oxygen vacancy accumulation at the domain walls. Ferroelectric materials, which usually consist of several domains, display an interesting property: they undergo a phase transition at a certain temperature, accompanied with a spontaneous polarization that can be switched through external electric fields. The existence of their two stable phases has proven useful in solid-state memory devices. Recently, switchable polarization in thin films of the ferroelectric material BiFeO3 has also been shown to display a diode effect (current directionality) and another very attractive property — photovoltaic behavior. However, its current generation under light irradiation arises from a different mechanism to that conventionally observed in semiconductors. Investigating the phenomenon through photocurrent imaging, a research group led by Moon-Ho Jo from Yonsei University in Korea found that the current generated depends on the domain structure of BiFeO3 and on the oxygen vacancy migration at the domain boundaries, which has exciting implications for future ferroelectric photovoltaic cell and optoelectronic device components. We demonstrate a single-domain photovoltaic switch based on lateral BiFeO3 channels, in which such photovoltaic switching is achieved by a coherent single-domain reversal with a short electrical pulse. We then provide visual evidence for such operations with a series of spatially and spectrally resolved short circuit photocurrent images. Specifically, it reveals that the sequential photovoltaic current images directly reflect the remanent polarization states of a single-domain channel. We also verify that, in multidomain channels, the diffusive switching characteristics is determined not only by the internal polarization vector within the domain but also by oxygen vacancy migration at the domain walls.