Surface and sub-surface processes which occurred during the growth of hydrogenated amorphous material were analyzed in order to understand how dangling-bond defects and weak bonds formed. It was found that the removal or addition of adsorbed SiH3 radicals gave a surface-defect density which decreased continuously with decreasing temperature; with no minimum near to 250C. It therefore could not be the process that defined defect densities in the bulk. The elimination of H, to create the bulk Si-Si network, occurred because the chemical potential of H caused the expulsion of H from the bulk. This H elimination was the rate-limiting step at lower temperatures, as its diffusion was slow. The difficulty of eliminating H led to the formation of weak bonds. The latter arose at higher deposition temperatures, via thermal disorder. The dangling-bond defects arose from weak bonds via the defect-pool process, and this process was assumed to continue down to temperatures, that were lower than normal, in the growth zone. Processes such as ion bombardment, which dehydrogenated the surface layers, could lower the weak-bond densities.

Deposition Mechanism of Hydrogenated Amorphous Silicon J.Robertson: Journal of Applied Physics, 2000, 87[5], 2608-17