Scalable fabrication of Hemispherical Solid Immersion Lenses in Silicon Carbide by Greyscale Lithography

Microscale solid immersion lenses (SILs) can enable efficient extraction of single photons from single solid-state quantum emitters. In solid-state matrices, photon collection is limited by total internal reflection, which traps most of the emission into the high-index medium. By removing refraction at large angles, SILs can boost collection efficiency by a factor 10-20, as shown for example for the spin/photon interface associated with single nitrogen-vacancy (NV) centers in diamond. SILs are typically fabricated by Focused Ion Beam, a process which is inherently non-scalable, slow and expensive.

Here we discuss the fabrication of SIL structures in silicon carbide using a novel fabrication protocol based on grayscale lithography, which allows nearly hemispherical lenses of 5 μm radius to be etched into the substrate. The technique is fully scalable and compatible with industrial processing, and device aspect ratios and shapes can further be tuned after resist patterning by controlling the chemistry of the subsequent dry etch. We benchmark the performance of the structures in improving photon collection efficiency fromsingle silicon vacancy centers in SiC, showing an enhancement by a factor 4, on average, for lenses not registered non the emitters' positions. These results provide a low-cost, high-throughput and industrially-relevant alternative to Focused Ion Beam milling for the creation of rounded micrometre-scale structures.