Amorphous silicon-filled gaps may be formed having no or a low occurrence of voids in the amorphous silicon fill, while maintaining a smooth exposed silicon surface. A gap in a substrate may be filled with amorphous silicon by heating the substrate to a deposition temperature between 300 and 500° C. and providing a feed gas that comprises a first silicon reactant to deposit an amorphous silicon film into the gap with an hydrogen concentration between 0.1 and 10 at. %. The deposited silicon film may subsequently be annealed. After the anneal, any voids may be reduced in size and this reduction in size may occur to such an extent that the voids may be eliminated.