Fabrication and Characterization of Nanopillar Arrays in 4H-SiC for Si Vacancy-based Quantum Sensing

Defect-based quantum sensing has emerged as a powerful technique for nanoscale magnetic field imaging. Among candidate materials, silicon carbide (4H-SiC) offers several advantages, including established CMOS-compatible fabrication methods and the ability to grow thin epilayers with spin coherent defects. A major challenge, however, lies in efficiently collecting photoluminescence (PL) from defects embedded within SiC, due to its high index of refraction. Additionally, for silicon vacancy centers ($V_{Si}$), resonant excitation and PL collection are weaker along the c-axis, which is typically normal to the surface. In this work, we investigate the integration of $V_{Si}$ centers into nanopillar arrays designed to enhance optical collection and excitation. We characterize the resulting structures through room-temperature PL measurements, as well as optically detected magnetic resonance (ODMR) measurements. Simulations performed in COMSOL are used to model the expected collection efficiencies. Experimentally, we observe more than an order-of-magnitude enhancement in PL intensity from defects incorporated into nanopillar arrays relative to bulk SiC, and little change in ODMR linewidth, demonstrating a promising approach for improving signal collection in SiC-based quantum sensors.