Fundamental chemical and physical considerations indicate that the basic mechanism that limits high growth rates of a-Si and alloy film is not just radical diffusion on the surface, but rather the elimination of excess hydrogen from the surface and subsurface. The elimination of H through the cross-linking of neighboring hydrogen atoms bonded to adjacent Si atoms at the surface, as postulated in the standard model of growth, is not thermodynamically likely. Rather, the elimination of excess H is facilitated both by H ions and radicals, and by bombardment by inert ions. The absence of efficient elimination results in voids and clustered H at the surfaces of voids, leading to excess Staebler-Wronksi de gradation. Therefore, to improve the quality of hot-wire materials and devices, efficient H, and perhaps inert ion bombardment, needs to be included during growth.