Circular GaN Membrane Gratings

This letter presents the fabrication and characterization of freestanding circular GaN gratings on a GaN-on-silicon platform. Optical modes propagate within the freestanding GaN membrane and their number decreases as the thickness of GaN membrane is reduced. Backside thinning of freestanding GaN membranes is used to obtain thinner GaN membranes that are helpful to reduce resonance modes and to broaden the reflectance interference fringes in the visible range. Strong coupling between the incident light and the circular grating is confirmed by angular-resolved reflectance measurement. The influences of the grating parameters on the reflectance spectra are investigated. This letter opens the way to fabricate single-layer GaN resonant gratings in the visible wavelength range.