GaN microring waveguide resonators bonded to silicon substrate by a two-step polymer process.

Abstract

Using a polymer bonding technique, GaN microring waveguide resonators were fabricated on a Si substrate for future hybrid integration of GaN and Si photonic devices. The designed GaN microring consisted of a rib waveguide having a core of 510nm in thickness, 1000nm in width, and a clad of 240nm in thickness. A GaN crystalline layer of 1000nm in thickness was grown on a Si(111) substrate by metal organic chemical vapor deposition using a buffer layer of 300nm in thickness for the compensation of lattice constant mismatch between GaN and Si crystals. The GaN/Si wafer was bonded to a Si(100) wafer by a two-step polymer process to prevent it from trapping air bubbles. The bonded GaN layer was thinned from the backside by a fast atom beam etching to remove the buffer layer and to generate the rib waveguides. The transmission characteristics of the GaN microring waveguide resonators were measured. The losses of the straight waveguides were measured to be 4.0±1.7 dB/mm around a wavelength of 1.55μm. The microring radii ranged from 30 to 60μm, where the measured free-spectral ranges varied from 2.58 to 5.30nm. The quality factors of the microring waveguide resonators were from 1710 to 2820.