Submicron Embedded Air/GaN Diffraction Gratings for Photonic Applications

The integration of photonic elements with nitride optoelectronic structures allows control of emitted light properties, which is advantageous for achieving, e.g., a single wavelength lasing. Positioning of the photonic structures on the top surface of GaN-based devices is problematic, in particular, for deposition of a metal contact to p-type top layer. In this work, custom-shaped submicron air channels arranged periodically 150 nm below the sample surface, forming an air/GaN diffraction grating embedded within a volume of the structure is proposed and fabricated. The fabrication process includes selective area Si ion implantation, GaN regrowth using plasma-assisted molecular beam epitaxy, ultra-high-pressure annealing for efficient electrical activation of implanted Si without diffusion, and electrochemical etching for the removal of selectively doped material. Embedded air/GaN diffraction gratings with periodicity of 460 and 631 nm are shown. Width of air channels ranges from 46 to 320 nm. Angle and polarization resolved reflectivity measurements combined with theoretical modeling confirm the designed optical performance of the embedded diffraction gratings in the GaN volume. The presented design and fabrication of custom-shaped, fully integrated photonic structures buried below the surface paves the way for novel type constructions of optoelectronic devices, such as compact distributed feedback laser diodes.