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.