Scalable fabrication of hemispherical solid immersion lenses in silicon carbide through grayscale hard-mask lithography

Abstract

Grayscale lithography allows the creation of micrometer-scale features with spatially controlled height in a process that is fully compatible with standard lithography. Here, solid immersion lenses are demonstrated in silicon carbide using a fabrication protocol combining grayscale lithography and hard-mask techniques to allow nearly hemispherical lenses of 5μm radius to be etched into the substrate. Lens performance was benchmarked by studying the enhancement obtained in the optical collection efficiency for single quantum emitters hosted in silicon carbide. Enhancement by a factor of 4.4 ± 1.0 was measured for emitters not registered to the center of the lens, consistent with devices fabricated through other methods. The grayscale hard-mask technique is highly reproducible, scalable, and compatible with CMOS technology, and device aspect ratios can be tuned after resist patterning by controlling the chemistry of the subsequent dry etch. These results provide a reproducible, low-cost, high-throughput and industrially relevant alternative to focused ion beam milling for the creation of high-aspect-ratio, rounded microstructures for quantum technology, and microphotonic applications.

Quantum systems in silicon carbide for sensing applications

“…Most of the magnetometry in SiC is based on DC magnetometry. For DC magnetometry based on ODMR, the most common approach used so far, higher sensitivity can be achieved by simply improving the photon collection efficiency using, for example, waveguides [56,171], nanopillars [172,173] and solid immersion lenses [174,175]. Another approach for increasing the spin read-out contrast for magnetometry in SiC defects could be based on achieving strong coupling by using high-Q macroscopic microwave cavities [176,177].…”

Fabrication of Large-Area Silicon Spherical Microlens Arrays by Thermal Reflow and ICP Etching

“…The fabrication processes of microlens arrays include ultra-precision machining technologies [11][12][13][14][15], laser direct writing [16][17][18], grayscale lithography [19,20], nanoimprint lithography [21][22][23][24], and thermal reflow processes [25][26][27][28]. Ultra-precision machining technologies, such as single point diamond turning (SPDT), are capable of fabricating microstructures with complex morphology and excellent precision.…”

Precise Characterization of a Waveguide Fiber Interface in Silicon Carbide

“…Recently, the silicon monovacancies at hexagonal (V1) and cubic (V2) lattice sites in 4H-SiC attracted attention, since they implement optically active spin qubits in an industrial semiconductor material. Both, V1 and V2 centers show long spin coherence times, 1,2 and provide access to a nuclear spin qubit register based on 13 C and 29 Si species. 3,4 Both centers show robust optical properties with lifetime-limited linewidths up to temperatures of 20 K 5 for V2.…”

“…This scenario can in principle happen for polarized nuclear spins. However, it is very unlikely that 7 out of 8 emitters are coupled to nearby nuclear spins and at the same time polarized in one energy level, considering that the sample contains only a limited number of nuclei with a nonzero magnetic moment, 4.7% of 29 Si and 1.1% of 13 C atoms. Second, we exclude an electric field originating from point defects (such as carbon vacancies) or foreign atoms (such as nitrogen atoms) in the local environment, which could shift the ground state spin levels via the Stark effect.…”

“…However, all experiments were operated at low photon detection rates, 10–30 kilo-counts per second, which is partially attributed to strong coupling to a long-lived metastable state. − Additionally, as all emitters in solid matter, photon collection efficiencies are ultimately restricted by total internal reflection at small emission angles, which hinders photons from leaving the host crystal. To slightly reduce the effect of total internal reflection, emitters can be integrated into solid immersion lenses, , as well as subwavelength sized structures, such as nanocrystals, and membranes . Further improvements can be achieved with structures that provide light guiding features such as circular Bragg gratings, nanopillars, as well as 1D photonic waveguides .…”