  Using metal-ferroelectric junctions as switchable diodes was proposed several
decades ago. This was shown to actually work in PbZr(1-x)TixO3 (PZT) by Blom et
al. [P.W. M. Blom et al., Phys. Rev. Lett. 73, 2107 (1994)], who reported
switching in the rectification direction and changes of the current of about 2
orders of magnitude upon switching the polarization direction of the
ferroelectric layer. This form of resistive switching enables the read out of a
ferroelectric memory state at higher speed compared to the capacitive design,
without destroying the information in each reading cycle. Recently, Jiang and
coworkers have shown that these Schottky barrier effects are enormous in
BiFeO3, giving thousand times more switched charge than found by in PZT [A.Q.
Jiang. et al., Adv. Mat. 23, 1277 (2011)]. Here, by performing local
conductivity measurements, we attribute this to a large change of the Schottky
barrier height between the as-grown, down-polarized domains and the
up-polarized domains. These measurements allow to estimate the relative effect
of polarization charges and screening charges on the conduction through the
ferroelectric.
