Towards high deposition rates of a-Si:H: The limiting factors

In the last few years, considerable progress has been made in the understanding of a-Si-H growth processes. Deposition rate and surface temperature have been found to be the main factors governing film quality. Many models have been proposed to describe their influence on the growth and give guides for further improvement of a-Si:H quality. Owing to the complexity of the plasma, these models usually take into account only certain aspects of the deposition, thus restricting their applicability to a small parameter space. By taking into account all plasma processes, we come to the conclusion that overall, the main limiting factor for low defect density a-Si:H deposition at high rates is plasma polymerization, but not powder formation. Moreover, when this limitation is overcome, the deposition of a-Si:H by RF glow discharge can be considered as a process out of equilibrium in which a-Si:H films are obtained in a metastable state governed by the plasma conditions. From this point of view, light-induced degradation can be considered as a supply of energy which causes the sample to attain another metastable state.