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

摘要

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 similar to 10 Angstrom /min, exhibited a sigma (Ph) similar to 1 x 10(-4) S cm(-1), sigma (Ph)/sigma (D) similar to 10(5), 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 muc-Si:H films were prepared with a high sigma (D) similar to 1 x 10(-4) S cm(-1), at a deposition rate of 30 Angstrom /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 H-2-diluted plasma. (C) 2001 American Institute of Physics. References: 32