Breaking the optical loss barrier in amorphous silicon across the full visible spectrum via dopant-controlled chemical vapor deposition

The propagation of light in nanophotonic structures is governed by the refractive index and optical dispersion of constituent materials. However, the choice of dielectrics is often restricted within the transparency window. We introduce object-driven engineering of the process of silicon-based dielectric materials for metasurfaces: visibly transparent hydrogenated amorphous silicon (a-Si:H) with a high refractive index of 3.48 and oxygen-doped a-Si:H (a-SiO_x:H) exhibiting strong dispersion (Abbe number < 10). Both films are fabricated via chemical vapor deposition with precise control over atomic bonding and dopants, revealing the link between optical properties and the amorphous silicon network. We demonstrate the effectiveness of a-Si:H in metalenses with conversion efficiencies of 66.3, 92.0, and 97.0% at 450, 532, and 635 nanometers, respectively. In addition, a wavelength-decoupled a-SiO_x:H beam-splitter achieves a 3.67-fold steering intensity contrast between 450 and 635 nanometers. These materials broaden the dielectric design space and enhance the performance of nanophotonic devices across the visible spectrum.