  Color-center defects in silicon carbide promise opto-electronic quantum
applications in several fields, such as computing, sensing and communication.
In order to scale down and combine these functionalities with the existing
silicon device platforms, it is crucial to consider SiC integrated optics. In
recent years many examples of SiC photonic platforms have been shown, like
photonic crystal cavities, film-on-insulator waveguides and micro-ring
resonators. However, all these examples rely on separating thin films of SiC
from substrate wafers. This introduces significant surface roughness, strain
and defects in the material, which greatly affects the homogeneity of the
optical properties of color centers. Here we present and test a method for
fabricating monolithic single-crystal integrated-photonic devices in SiC:
tuning optical properties via charge carrier concentration. We fabricated
monolithic SiC n-i-n and p-i-n junctions where the intrinsic layer acts as
waveguide core, and demonstrate the waveguide functionality for these samples.
The propagation losses are below 14 dB/cm. These waveguide types allow for
addressing color-centers over a broad wavelength range with low strain-induced
inhomogeneity of the optical-transition frequencies. Furthermore, we expect
that our findings open the road to fabricating waveguides and devices based on
p-i-n junctions, which will allow for integrated electrostatic and radio
frequency (RF) control together with high-intensity optical control of defects
in silicon carbide.
