Effect of Fabrication Methods of Amorphous Silicon on the Ultrafast Dynamics of Dielectric Metasurfaces*

We demonstrate how various fabrication methods of amorphous silicon can drastically modify the ultrafast optical properties of dielectric metasurfaces. Silicon thin films were made using either electron beam evaporation or plasma-enhanced chemical vapor deposition. The fabricated samples were fully characterized optically and structurally via ellipsometry and X-ray diffraction respectively. Moreover, we use linear and ultrafast nonlinear spectroscopy to understand the effect of two-photon absorption, free carrier relaxation, and lattice heating on the overall optical response of our various samples. To confirm results of our ultrafast optical experiments, we modelled the dynamics using a differential model coupled to a full-field finite-difference time-domain electromagnetic solver that accurately reproduces our experimental observations.