Electrode interface control of the Schottky diode-like behavior in epitaxial Pb(Zr_0.2Ti_0.8)O₃ thin films: A critical analysis

Metal-ferroelectric-metal structures based on epitaxial Pb(Zr_0.2Ti_0.8)O₃ thin films are prepared by pulsed laser deposition on single crystal SrTiO₃ substrates ((001) orientation) with buffer SrRuO₃ layer as bottom electrode. Pt, Cu, and SrRuO₃ are used as top contacts. The current-voltage (I–V) measurements reveal a strong influence of the top electrode interface on the magnitude of the leakage current and the shape of the I–V characteristics. The lowest current values are obtained for top Cu and the highest for top Pt. Diode-like behavior is obtained for top Cu and Pt, but the forward and reverse biases are opposite in sign. Contrary to the case of BiFeO₃ layers deposited on the same type of substrates, it was found that the diode-like behavior is not switchable with the polarization reversal although the polarization values are comparable. It is also shown that the metal-ferroelectric-metal (MFM) structure based on Pb(Zr,Ti)O₃ (PZT) can be simulated and modeled as a back-to-back connection of two Schottky diodes. The diode-like behavior of the MFM structure can be induced by a slight asymmetry of the potential barriers at the electrode interfaces behaving as Schottky contacts. The study ends with a critical discussion of the MFM structures based on PZT and BiFeO₃ (BFO) layers. It is shown that the switchable diode-like behavior is not uniquely determined by the polarization reversal and is not a general characteristic for MFM structures. Such behavior may be present only if the polarization induced band-bending at the interface is generating an accumulation layer at the interface. This could be possible in BiFeO₃ based MFM structures due to the lower band gap compared to Pb(Zr_0.2Ti_0.8)O₃ thin films.