Passivated SiC Surfaces for Photonic and Quantum Applications: Balancing Chemical Stability and Surface Luminescence

ABSTRACT Silicon carbide (SiC) has emerged as a promising platform for photonic and quantum technologies, yet the role of surface passivation, particularly at low processing temperatures, remains insufficiently understood with respect to long‐term optical stability. Here, we present a systematic study of low‐temperature surface passivation strategies for 4H‐SiC, including atomic layer deposition of Al ₂ O ₃ and HfO _x , plasma‐enhanced chemical vapor deposition of SiN _x and SiO ₂ , as well as Ar and CF ₄ plasma treatments. Surface morphology, chemistry, wettability, and optical background were investigated using atomic force microscopy, X‐ray photoelectron spectroscopy, contact angle measurements, and spatially resolved photoluminescence (PL) imaging, with particular emphasis on environmental stability under ambient conditions. While CF ₄ plasma and ALD‐HfO _x yield chemically robust surfaces, they do not significantly suppress photoluminescence. In contrast, Ar plasma and PECVD‐SiN _x treatments produce smooth surfaces with strongly reduced and spatially homogeneous PL background, with SiN _x exhibiting the best overall performance. Notably, both Ar plasma‐ and SiN _x ‐passivated surfaces preserve their low PL background even after 1 year of ambient storage. These results demonstrate that optical surface quality is not directly correlated with chemical robustness and must be optimized independently. This work establishes design guidelines for passivation strategies in SiC‐based photonic and quantum devices.