Polarity control of carrier injection at ferroelectric/metal interfaces for electrically switchable diode and photovoltaic effects

TL;DR

This paper demonstrates a ferroelectric diode effect in Pt/BiFeO3/SrRuO3 capacitors, showing how polarization control at interfaces modulates carrier injection and enables switchable diode and photovoltaic functionalities.

Contribution

It reveals the physical mechanism of polarization-controlled carrier injection at ferroelectric/metal interfaces, enabling electrically switchable diode and photovoltaic effects.

Findings

Diode polarity can be switched by ferroelectric polarization reversal.

Polarization affects the Schottky barrier and carrier injection.

Switchable diode behavior correlates with ferroelectric domain states.

Abstract

We investigated a switchable ferroelectric diode effect and its physical mechanism in Pt/BiFeO3/SrRuO3 thin-film capacitors. Our results of electrical measurements support that, near the Pt/BiFeO3 interface of as-grown samples, a defective layer (possibly, an oxygen-vacancy-rich layer) becomes formed and disturbs carrier injection. We therefore used an electrical training process to obtain ferroelectric control of the diode polarity where, by changing the polarization direction using an external bias, we could switch the transport characteristics between forward and reverse diodes. Our system is characterized with a rectangular polarization hysteresis loop, with which we confirmed that the diode polarity switching occurred at the ferroelectric coercive voltage. Moreover, we observed a simultaneous switching of the diode polarity and the associated photovoltaic response dependent on the ferroelectric domain configurations. Our detailed study suggests that the polarization charge can affect the Schottky barrier at the ferroelectric/metal interfaces, resulting in a modulation of the interfacial carrier injection. The amount of polarization-modulated carrier injection can affect the transition voltage value at which a space-charge-limited bulk current-voltage (J-V) behavior is changed from Ohmic (i.e., J ~ V) to nonlinear (i.e., J ~ V^n with n \geq 2). This combination of bulk conduction and polarization-modulated carrier injection explains the detailed physical mechanism underlying the switchable diode effect in ferroelectric capacitors.