Characteristics of intrinsic protocrystalline silicon films prepared by photo-CVD method

We investigated the light-soaked behaviors of hydrogen diluted amorphous silicon films and solar cells using the films as active layers. The films were fabricated at various hydrogen dilution ratios by using a mercury-sensitized photo-chemical vapor deposition system. We found a moderate hydrogen dilution ratio where the stable phase protocrystalline silicon, a transient material prepared just before onset of microcrystalline regime, can be obtained. We observed that the films prepared at the onset of microcrystalline regime is unstable in spite of the facts that the films have: i) more blue-shifted amorphous TO phonon bands; ii) nano-sized crystalline silicon grains; and iii) lower broadening parameters (C) in comparison with protocrystalline silicon. We claim two new facts from our experiments: i) the relatively high stability of the protocystalline silicon is attributed to the densest amorphous silicon network structure; ii) the decreased stability at the onset of microcrystallization is due to clustered hydrogen bonds accompanied by high atomic hydrogen content.