Evidence for the participation of atomic H in the light-induced metastability of hydrogenated amorphous material was observed by means of low-temperature infra-red transmission spectroscopy and room-temperature infra-red phase-modulated ellipsometry. A band at 1730/cm, accompanied by an increase in the amplitude of the bending mode of a new broad band at about 870/cm, was observed after 1h of intense illumination of an annealed amorphous hydrogenated sample. A shift of this band to lower frequencies was observed during prolonged light-soaking, and the band disappeared after about 4h of illumination. At the same time, the density of the atomic H which was bonded to Si decreased; as deduced from the area under the broad band at about 640/cm. The results could be interpreted in terms of a H diffusion model in which the H atom of a Si-H bond next to a weak Si-Si bond diffused so as to form a 3-center bond at intermediate illumination times. It then diffused further so as to form a stable Si-H bond at longer times.

R.Darwich, P.Roca i Cabarrocas, S.Vallon, R.Ossikovski, P.Morin, K.Zellama: Philosophical Magazine B, 1995, 72[3], 363-72