Densities of states of a large set of samples were 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 could account for this behavior, a new model was proposed. In this model, light-induced creation of dangling

bonds was mediated by interstitial H. Hydrogen coming from the breaking of Si-H bonds was trapped into voids or platelets during light soaking and released in the lattice during annealing. This model fully explained the present experimental results and also many other published experimental observations.

Role of Interstitial Hydrogen and Voids in Light-Induced Metastable Defect Formation in Hydrogenated Amorphous Silicon - a Model. C.Longeaud, D.Roy, O.Saadane: Physical Review B, 2002, 65[8], 085206 (9pp)