Polarization-switching Pathway Determined Electrical Transport Behaviors in Rhombohedral BiFeO3 Thin Films.

We investigated the polarization-switching pathway-dependent electrical transport behaviors in rhombohedral-phase BiFeO3 thin films with point contact geometry. By combining conducting-atomic force microscopy and piezoelectric force microscopy, we simultaneously obtained current-voltage curves and the corresponding domain patterns before and after the polarization switching. The results indicate that for the (001)-oriented film, the abrupt current (due to polarization reversing) increases with the enhanced switching voltage for 109° and 180° switching events. More importantly, the abrupt current can be further improved in (110)- and (111)-oriented thin films, which benefits from the stronger modulation of the interfacial Schottky barrier by the enhanced out-of-plane polarization magnitude. The current on-off ratio obtained in a ∼20 nm thick (111)-oriented BiFeO3 thin film at a readout voltage of ∼3 V exceeds (∼6 × 105)%, which is close to the result from a previous report on ultrathin tetragonal BiFeO3 thin films.