(Invited) Aberration-Corrected STEM Characterization of Nitride Ferroelectrics

The new class of wide bandgap nitride ferroelectrics has emerged as potential materials for many optoelectronic and electronic applications due to their high remanent polarization and tunable coercive field. In addition, their coupling to plasmonic materials promises new levels of spectral emission tunability. The change in the ferroelectric polarization could modulate the carrier concentration at the ferroelectric/plasmonic heterointerface. The massive polarization is now available for the Al1-xBxN group of materials, promising new levels of accumulation and depletion of carriers at the heterointerface. With the polar orientation-induced changes in the free charge carriers, tunable optical responses in the plasmonic materials are expected. In this study, we demonstrate that aberration-corrected scanning transmission electron microscopy (STEM) and differential phase contrast (DPC) imaging are powerful tools for characterizing ferroelectric/plasmonic interfaces at the nanoscale. By measuring the phase shifts induced by the specimen’s electric field, this method provides enhanced sensitivity and direct visualization of subtle variations in the electrostatic potential inside the material. This technique is used to study the heterointerfaces of ferroelectric/substrate and ferroelectric/plasmonic matter to map electromagnetic fields at atomic resolution. Here, we present the pathway to directly visualize the atomic configurations to distinguish between the polarization orientations (i.e., “up” or “down” polarization), the polarization reversal, and the induced effect of the polarization switching on the local free carriers. Understanding the changes in the atomic configurations in the ferroelectric layer and near the heterointerfaces will push the limits of design toward more efficient optoelectronic devices.