Nonstoichiometry, Structure, and Properties of BiFeO₃ Films

Abstract

We explore the effect of growth conditions on the cation and anion chemistry, electrical leakage, conduction mechanisms, and ferroelectric and dielectric behavior of BiFeO 3. Although it is possible to produce single-phase, coherently strained films in all cases, small variations in the pulsed-laser deposition growth process, specifically the laser repetition rate and target composition, result in films with chemistries ranging from 10% Bi-deficiency to 4% Bi-excess and films possessing Bi gradients as large a 6% across the film thickness. Corresponding variations and gradients in the O chemistry are also observed. As a result of the varying film chemistry, marked differences in surface and domain morphology are observed wherein Bi-deficiency stabilizes atomically smooth surfaces and ordered stripe domains. Subsequent investigation of the current−voltage response reveals large differences in leakage current density arising from changes in both the overall stoichiometry and gradients. In turn, the film stoichiometry drives variations in the dominant conduction mechanism including examples of Schottky, Poole−Frenkel, and modified Poole−Frenkel emission depending on the film chemistry. Finally, slightly Bi-excess films are found to exhibit the best low-frequency ferroelectric and dielectric response while increasing Bi-deficiency worsens the low-frequency ferroelectric performance and reduces the dielectric permittivity.

Formation of BiFeO3 from a Binary Oxide Superlattice Grown by Atomic Layer Deposition

“…However, there is little understanding of how the as‐grown amorphous films crystallize during post‐deposition heat treatment, which is required for ALD‐grown BFO films. In particular, for polycrystalline films both, composition and microstructure, have tremendous effects on the resulting properties …”

“…[24,25] However,t here is little understanding of how the as-grown amorphous films crystallize duringp ost-deposition heat treatment,w hich is requiredf or ALD-grown BFO films. In particular, for polycrystalline films both, composition [26] and microstructure, have tremendous effects on the resulting properties. [27] In this report, we provideadetailed investigation of the crystallization of Bi-Fe-Of ilms grown via as uperlattice approach.H erein, semi-amorphous Fe 2 O 3 -Bi 2 O 3 superlattices were studied by in situ X-ray diffraction (XRD) and X-ray reflectivity (XRR), in situ X-ray photoelectron spectroscopy (XPS), scanning transmission electronm icroscopy( STEM) and transmission electron microscopy (TEM) after annealing at selected temperatures (T).…”

Electronic Transport and Ferroelectric Switching in Ion‐Bombarded, Defect‐Engineered BiFeO3 Thin Films

“…Considerable effort in modern materials science has focused on the quest for multifunctional materials with novel or enhanced responses as a means to meet the needs of a diverse range of applications. Complex‐oxide ferroelectric thin films have been extensively studied due to the existence of spontaneous switchable polarization and strong coupling between their electrical, mechanical, thermal, and optical responses . Among complex‐oxide ferroelectrics, BiFeO 3 has attracted considerable attention due to its multiferroic nature (i.e., coexistence of a large spontaneous polarization and G‐type antiferromagnetism), and potential for strong magnetoelectric coupling .…”

“…Therefore, careful understanding of the interplay between defects and materials response, as well as establishing routes to control the type and concentration of defects, are crucial for fine‐tuning and optimization of the properties of BiFeO 3 thin films. For example, point defects often give rise to high leakage and losses via doping of the lattice with charge which can limit the application of BiFeO 3 thin films in electronic devices . In turn, developing routes to enhance the resistivity of BiFeO 3 remains an important materials challenge.…”

MOCVD Growth of Perovskite Multiferroic BiFeO3 Films: The Effect of Doping at the A and/or B Sites on the Structural, Morphological and Ferroelectric Properties

“…Considerable efforts have been devoted to the synthesis of BiFeO 3 at the nanoscale level and to the study of its ferroelectric properties, but for the above mentioned applications BiFeO 3 is required in thin film forms. Up to date, BiFeO 3 films have been deposited on various substrates using physical vapor deposition techniques such as pulsed laser deposition (PLD), molecular beam epitaxy and sputtering . Atomic layer deposition has been recently applied to the deposition of thin or ultrathin films of BiFeO 3 using a laminar layer approach, alternating deposition of the binary oxides followed by annealing at higher temperature .…”