Frank-type stacking faults in 4H-SiC: A unified crystallographic, thermodynamic, electronic, and optical framework

Frank-type stacking faults (FSFs) are among the most important extended defects in 4H-SiC, yet their crystallographic classification, transformation mechanisms, electronic structures, and optical properties remain incompletely understood. Here, we present a comprehensive investigation of FSFs in 4H-SiC through the integration of high-angle annular dark-field high-resolution scanning transmission electron microscopy (HAADF HR-STEM), photoluminescence (PL) mapping and spectroscopy, and density functional theory (DFT) calculations. By rigorously applying Frank’s original crystallographic definition, we resolve long-standing ambiguities in the intrinsic/extrinsic classification of FSFs and demonstrate that the widely discussed (3,2) FSF is intrinsically classified despite involving an insertion-mediated formation process. Direct atomic-scale observations further reveal structural connectivity among the standard (5,2), (4,2), and (4,1) FSFs, providing experimental support for one possible crystallographic evolution pathway linking these faults. Investigations of non-standard FSFs show that identical Zhdanov notations can correspond to either intrinsic or extrinsic fault configurations depending on their crystallographic topology. DFT calculations establish, for the first time, comprehensive stacking-fault energies and electronic band structures for both standard and non-standard FSFs. While most FSFs exhibit conventional 3C-like quantum-well states, the (1,1) and (2,1) FSFs display distinct 2H-like electronic characteristics associated with dominant K-point split-off states. Finally, direct HR-STEM/PL correlation and first-principles calculations identify the characteristic PL emission wavelength of the standard (4,1) FSF as 459 nm, demonstrating that the long-accepted 424 nm assignment is inconsistent with both experimental and theoretical evidence. These results establish a unified crystallographic, thermodynamic, electronic, and optical framework for FSFs in 4H-SiC.