Influence of thermal growth of Au nanoparticles in the coupling efficiency of Au/SiO₂ nanocomposite grating coupler

The Au/SiO₂ nanocomposite grating coupler with a period of 600 nm was fabricated by implantation of 140 keV Au ions at a fluence of 6 × 10¹⁶ ions·cm⁻² in combination with subsequent electron-beam lithography and ion beam etching. The thermal evolution of Au nanoparticles and its influence on the vertical coupling efficiency of the prepared grating coupler has been investigated in detail. The results clearly show that the coupling efficiency of the nanocomposite grating coupler could be affected by the thermal evolution of Au nanoparticles, which increases in the annealing temperature range up to 800 °C, and then decreases at 900 °C and above. Theoretical calculation demonstrates that the change of the coupling efficiency should be closely related to the synergistic effect of the scattering effect and the variation in the volume fraction of Au nanoparticles due to the thermal growth. (paper)