Densities of states of a large set of samples have been measured. Samples were deposited by radio-frequency powered glow discharge under various conditions of temperature, power, gas pressure, and dilution of silane. Density of states was studied in the as-deposited, light-soaked, and annealed states. For all the samples light soaking resulted in an increase of both the deep defect density and of the conduction-band tail states. For samples deposited on the edge of crystallinity and polymorphous materials irreversible modifications of the density of states were observed after light soaking followed by annealing. Since none of the existing models of the metastability can account for this behavior we propose a model. In this model, light induced creation of dangling bonds is mediated by interstitial hydrogen. Hydrogen coming from the breaking of Si-H bonds is trapped into voids or platelets during light soaking and released in the lattice during annealing. This model fully explains our experimental results and also many other experimental observations found in the literature.

• Received 10 April 2001

DOI:https://doi.org/10.1103/PhysRevB.65.085206