Structural and photo-luminescence properties of nanocrystalline silicon films deposited at low temperature by plasma-enhanced chemical vapor deposition

Nanocrystalline silicon (nc-Si) films were prepared by a plasma-enhanced chemical vapor deposition method at a deposition temperature below 220 °C with different dynamic pressures (P_g), hydrogen flow rates ([H₂]), and RF powers, using SiH₄/H₂/SiF₄ mixtures. We examined the photo-luminescence (PL) spectra and the structural properties. We observed two stronger and weaker PL spectra with a peak energies around E_PL = 1.8 and 2.2-2.3 eV, respectively, suggesting that the first band was related to nanostructure in the films, and another band was associated with SiO-related bonds. The nc-Si films with rather large PL intensity was obtained for high [H₂] and/or low pressure values, However, effects of [H₂] are likely to be different from those of P_g. The average grain size (δ) and the crystalline volume fraction (ρ) at first rapidly increase, and then slowly increase, with increasing P_g. Other parameters exhibited opposite behaviors from those of δ or ρ. These results were discussed in connection with the changes in the PL properties with varying the deposition conditions.