Intrinsic space charge layers and field enhancement in ferroelectric nanojunctions

Conducting characteristics of topological defects in ferroelectric materials, such as charged domain walls, engendered a broad interest on their scientific merit and the possibility of novel applications utilizing domain engineering. At the same time, the problem of electron transport in ferroelectrics still remains full of unanswered questions and becomes yet more relevant over the growing interest in ferroelectric semiconductors and new improper ferroelectric materials. We have employed self-consistent phase-field modeling to investigate the physical properties of a local metal-ferroelectric (Pb(Zr_0.2Ti_0.8)O₃) junction in applied electric field. We revealed an up to 10-fold local enhancement of electric field realized by large polarization gradient and over-polarization effects due to inherent non-linear dielectric properties of Pb(Zr_0.2Ti_0.8)O₃. The effect is independent of bias polarity and maintains its strength prior, during and after ferroelectric switching. The observed field enhancement can be considered on similar grounds as increased doping level, giving rise to reduced switching bias and threshold voltages for charge injection, electrochemical and photoelectrochemical processes.