An apparatus, device, system, and method for controlling the index of refraction of at least one layer of amorphous silicon-based film deposited on a substrate are disclosed. The apparatus, device, system and method include providing at least one volume of each of N2, SiH4, and He, and depositing the at least one layer of amorphous silicon-based film on the substrate by vapor deposition. The device may include a waveguide that includes at least one layer of amorphous silicon-based film, wherein the at least one layer of amorphous silicon-based film is deposited by vapor deposition using an at least one volume of each of N2, SiH4, and He.