In some embodiments, a method of processing a substrate disposed atop a substrate support in a physical vapor deposition process chamber includes: (a) forming a plasma from a process gas within a processing region of the physical vapor deposition chamber, wherein the process gas comprises an inert gas and a hydrogen-containing gas to sputter silicon from a surface of a target within the processing region of the physical vapor deposition chamber; and (b) depositing an amorphous silicon layer atop a first layer on the substrate, wherein adjusting the flow rate of the hydrogen containing gas tunes the optical properties of the deposited amorphous silicon layer.