Silicon oxynitride waveguides for optoelectronic integrated circuits

Planar optical waveguides on p-type Si wafers have been fabricated by a photo-induced deposition process. Silicon oxynitride was deposited using a gaseous mixture of SiH₄ (2% in Ar), NH₃ and N₂O under 253.7 nm UV radiation. The oxynitride composition was varied by changing N₂O: (N₂O + NH₃) ratio while keeping N₂O + NH₃ and SiH₄ flow rates constant. The refractive index varied from 1.46 to 1.95. The optical energy gap increased from 4.8 to 5.7 as the flow rate ratio varied from 0 to 0.25. Si-N bond shifts to higher energy owing to the incorporation of oxygen. A planar waveguide structure was fabricated using thermally grown SiO₂ buffer layer of 1.1 μm thickness. The loss was estimated to be 1.1 dB/cm for TE₀ mode at 632.8nm. The accuracy of measurements is 0.02 dB/cm.