Imaging the 3D Structure of Rare-Earth Dopant Defects and Clusters in SiC by Multislice Electron Ptychography

Rare earth ions hosted within wide-bandgap materials offer a promising platform for quantum information applications. Due to the significant size mismatch between rare earth dopants and the host lattice, ions such as samarium (Sm) tend to create complex defect structures and clusters. This complexity extends beyond single substitutions, interstitials, or vacancies and requires careful investigation. Dopant clustering, a well-known mechanism for defect deactivation in semiconductors, plays a critical role in altering material properties. Thus, understanding these dopants and their interactions at the atomic scale is essential for revealing activation mechanisms and refining doping strategies.
Here we employ multislice electron ptychography (MEP) to investigate the defect structures and clusters of Sm in silicon carbide (SiC), a wide-bandgap material that serves as a model system for exploring rare-earth-doped defect centers. Enabled by a new generation of high-dynamic range electron microscope detectors, MEP allows us to study the atomic distribution of dopants and defect structures with sub-Ångstrom lateral and nanometer-scale depth resolution, providing information not accessible through traditional TEM techniques. This technique has enabled us to visualize atomic-scale features, such as vibration envelopes and individual dopants, that are otherwise challenging to detect. Through MEP, we have cataloged a variety of defect structures and complex clusters of Sm in SiC along two different zone axes. We have observed that Sm dopants can form columns along silicon sites, displacing the neighboring carbons, while straining surrounding Si and C atoms, or grow to nanoparticles within the bulk, usually occupying interstitial positions and again introducing local strain. Furthermore, we present Density Functional Theory (DFT) calculations to provide insight into understanding the stability of our observed structures and the atomic-scale behavior of Sm dopants and defect formation mechanisms in SiC.