Ferroelectric domain scaling and electronic properties in ultrathin BiFeO3 films on vicinal substrates

TL;DR

This study demonstrates ferroelectric polarization and domain scaling in ultrathin BiFeO3 films on vicinal substrates, revealing domain behavior consistent with LLK law and analyzing electronic properties relevant for tunneling.

Contribution

It provides new insights into ferroelectric domain scaling and electronic properties of ultrathin BiFeO3 films using advanced microscopy and theoretical calculations.

Findings

Domain width scales with square root of thickness

Large effective barrier height of 3.6 eV in rhombohedral BFO

Lower barrier height of 0.38 eV in tetragonal BFO

Abstract

We report electrically switchable polarization and ferroelectric domain scaling over a thickness range of 5-100 nm in BiFeO3 films deposited on [110] vicinal substrates. The BiFeO3 films of variable thickness were deposited with SrRuO3 bottom layer using pulsed laser deposition technique. These films have fractal domain patterns and the domain width scales closely with the square root of film thickness, in accordance with the Landau-Lifschitz-Kittel (LLK) law. The Switching Spectroscopy Piezo-response Force Microscopy provides clear evidence for the ferroelectric switching behavior in all the films. Using Quasi-particle Self-consistent GW (QPGW) approximation we have investigated physical parameters relevant for direct tunneling behavior, namely the effective mass and effective barrier height of electrons. For rhombohedral BFO, we report a large effective barrier height value of 3.6 eV, which is in reasonable agreement with nanoscale transport measurements. QPGW investigations into the tetragonal BFO structure with P4mm symmetry revealed a barrier height of 0.38 eV, significantly lower compared to its rhombohedral counterpart. This difference has very significant implications on the transport properties of nearly tetragonal BFO phase.