Fabrication of GaN‐based ridge waveguides with very smooth and vertical sidewalls by combined plasma dry etching and wet chemical etching

GaN‐based ridge waveguides with very smooth and vertical sidewalls are fabricated by combined inductively coupled plasma (ICP) etching and wet chemical etching. The height of GaN waveguide is precisely controlled by ICP dry etching, while smooth and vertical sidewalls are realized by wet chemical etching. Compared with waveguides with rough sidewalls just after ICP etching, the propagation loss of waveguides with wet‐etched smooth sidewalls was reduced by about 2 dB mm−1 at 1.55 µm. Propagation loss can be further reduced by improving the quality of GaN epitaxial layers.