Heterogeneity in microcrystalline-transition state: origin of Si-nucleation and microcrystallization at higher rf power from Ar-diluted SiH₄ plasma

Abstract

Using very high Ar-dilution to the SiH₄ plasma, good quality amorphous Si:H films could be obtained at very low rf power. The a-Si:H film, prepared at a very low deposition rate of ~10 Å/min, exhibited a σ_Ph~1×10^-4Scm^-1,σ_Ph/σ_D~10⁵, a notably wide optical gap of 2.10 eV and a very good stability against thermal annealing effects with reasonable light induced degradation. At higher rf power undoped µc-Si:H films were prepared with a high σ_D~1×10 ^-4Scm^-1, at a deposition rate of 30 Å/min from <1 sccm of SiH₄. Micrograins were identified with several well-defined crystallographic orientations. However, porosity in the grain boundary zone contributed a significant amount of adsorbed effects on the electrical properties. At very high powers, the growth of a columnar network structure was demonstrated. Long-range structural relaxation permitted by the non-rigid and heterogeneous network structure associated with the physical vapor deposition-like growth at the microcrystalline-transition state, has been identified as the origin of nucleation to the Si network and microcrystallization at higher power. It is proposed that Ar in the Ar-diluted plasma provides the energy required for nucleation and grain growth during microcrystallization, and plays an analogous role as atomic H does during chemical annealing in H₂-diluted plasma.