  Wavelength-sized microdisk resonators were fabricated on a single crystalline
4H-silicon-carbide-oninsulator platform (4H-SiCOI). By carrying out
microphotoluminescence measurements at room temperature, we show that the
microdisk resonators support whispering-gallery modes (WGMs) with quality
factors up to $5.25 \times 10^3$ and mode volumes down to $2.69 \times(\lambda
/n)^3$ at the visible and near-infrared wavelengths. Moreover, the demonstrated
wavelength-sized microdisk resonators exhibit WGMs whose resonant wavelengths
compatible with the zero-phonon lines of spin defects in 4H-SiCOI, making them
a promising candidate for applications in cavity quantum electrodynamics and
integrated quantum photonic circuits.

Optics;Applied Physics