The large ferroelectric diode current modulated by bipolar polarization in epitaxial (111) BiFeO3 thin film has been observed. With the survey of different current leakage models, it is found that the space-charge limited current dominates the conduction. For the intrinsic physical understanding, the rectification of diode currents near domain coercive fields is attributed to gradient distribution of the trap charges between top and bottom electrode/ferroelectric interfaces, and the distributed charges can be reversed upon polarization reversal. Moreover, the retention time of the On and Off diode currents is over 104 s with their ratio of around 5:1.

Articles you may be interested inChemical solution deposition derived (001)-oriented epitaxial BiFeO3 thin films with robust ferroelectric properties using stoichiometric precursors (invited)

We fabricated (00l) BiFeO3 (BFO) thin films in different growth modes on SrRuO3/SrTiO3 substrates using a pulsed laser deposition technique. X-ray diffraction patterns show an out-of-plane lattice constant of 4.03 Å and ferroelectric polarization of 82 µC/cm2 for the BFO thin film in a layer-by-layer growth mode (2D-BFO), larger than 3.96 Å and 51 µC/cm2 for the thin film in the 3D-island formation growth mode (3D-BFO). The 2D-BFO thin film at 300 K shows switchable on/off diode currents upon polarization flipping near a negative coercive voltage, which is nevertheless absent from the above 3D-BFO thin film. From a positive-up–negative-down pulse characterization technique, we measured domain switching current transients as well as polarization–voltage (Pf–Vf) hysteresis loops in both semiconducting thin films. Pf–Vf hysteresis loops after 1 µs-retention time show the preferred domain orientation pointing to bottom electrodes in a 3D-BFO thin film. The poor retention of the domains pointing to top electrodes can be improved considerably in a 2D-BFO thin film. From these measurements, we extracted domain switching time dependence of coercive voltage at temperatures of 78–300 K. From these dependences, we found coercive voltages in semiconducting ferroelectric thin films much higher than those in insulating thin films, disobeying the traditional Merz equation. Finally, an equivalent resistance model in description of free-carrier compensation of the front domain boundary charge is developed to interpret this difference. This equivalent resistance can be coincidently extracted either from domain switching time dependence of coercive voltage or from applied voltage dependence of domain switching current, which drops almost linearly with the temperature until down to 0 in a ferroelectric insulator at 78 K.

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