Effect of doping on the amorphous to microcrystalline transition in a hydrogenated amorphous silicon under hydrogen plasma treatment

Just after their deposition, we have exposed intrinsic and doped hydrogenated amorphous silicon (a-Si:H) films to a hydrogen plasma. We have investigated, by in situ spectroscopic ellipsometry measurements, the structural evolution of the film during the amorphous to microcrystalline phase transition. To take into account the complex morphological development of microcrystalline silicon (μc-Si:H), the grown film is modeled by a graded layer with a linear index variation along the growth direction. By comparing the time evolution of the structural parameters of the deposited μc-Si:H layer, we have observed a particular behavior in the case of boron-doped a-Si:H. Despite a faster and deeper hydrogen diffusion from the beginning of hydrogen plasma exposure, and a later nucleation, a compact μc-Si:H layer is obtained. In the case of intrinsic and n -type a-Si:H the nucleation is faster and leads to a thin and very porous μc-Si:H layer. The particular behavior of the p -type material is attributed to the effects of boron, which, on the one hand, enhances the deposition of the Si precursors and, on the other hand, reduces the etching rate.