A freshly deposited B-doped, hydrogenated amorphous (a-Si:H) layer was exposed to H plasma under conditions of chemical transport. In situ spectroscopic ellipsometry measurements revealed that atomic H impinging on the film surface behaved differently before and after crystallization. Firstly, the plasma exposure increased H solubility in the a-Si:H network; leading to the formation of a H-rich sub-surface layer. Then, when the crystallization process began, the excess H started to leave the sample. This unusual evolution of excess H was attributed to the grown hydrogenated microcrystalline (μc-Si:H) layer, which gradually prevented the atomic H from the plasma reaching the μc-Si:H/a-Si:H interface. Consequently, H solubility, initially increased by the H plasma, recovered the initial value of untreated a-Si:H material. To support the theory that the out-diffusion was a consequence and not the cause of μc-Si:H layer growth, the combined diffusion and trapping equations, which governed H diffusion into the sample, were solved using appropriate approximations and a specific boundary condition which explained the lack of H injection during μc-Si:H layer growth.

Hydrogen Evolution During Deposition of Microcrystalline Silicon by Chemical Transport. N.Pham, P.Roca, I.Cabarrocas, A.Hadjadj, A.Beorchia, F.Kail, L.Chahed: Philosophical Magazine, 2008, 88[3], 297-311