We investigated the structural, electrical, and optical properties as well as light-induced degradation characteristics of silicon films prepared by photochemical vapor deposition at various hydrogen dilution ratios. The protocrystalline silicon deposited before the onset of the microcrystalline regime was most stable against light soaking. However, the films deposited at the onset of the microcrystalline regime, known to have the most competent device quality and stability, were observed to be less stable. Such instability at the onset of the microcrystalline regime is correlated with the existence of the clustered phase hydrogen that indicates microvoids in the films. (C) 2003 American Institute of Physics.