Optical attenuation in defect-engineered silicon rib waveguides

The excess optical attenuation at wavelengths around $1550\mathrm{nm}$ induced by subamorphous dose ion implantation of silicon-on-insulator rib waveguides has been quantified. Optical attenuation is related to the introduction of lattice defects such as the silicon divacancy. After $2.8\mathrm{MeV}$ ${\mathrm{Si}}^{+}$ implantation at a dose of $2.5\times {10}^{14}{\mathrm{cm}}^{-2}$ , the attenuation is greater than $1000\mathrm{dB}{\mathrm{cm}}^{-1}$ . Using positron annihilation spectroscopy to determine the vacancy-type defect concentration, it is demonstrated that the absorption component of the excess attenuation can be predicted using a simple analytical expression. Additional losses are suggested to result from a defect induced change in the real part of the refractive index of the silicon waveguide. A processing strategy for ensuring that the absorption component dominates the excess attenuation is described, and it is shown that selective implantation of a relatively low dose of inert ions is an efficient method for the reduction of optical cross talk in silicon photonic circuits.