OBSERVATION BY INFRARED TRANSMISSION SPECTROSCOPY AND INFRARED ELLIPSOMETRY OF A NEW HYDROGEN-BOND DURING LIGHT-SOAKING OF A-SI-H

Evidence for participation of atomic hydrogen in the Light-induced met astability mechanism of hydrogenated amorphous silicon (a-Si:H) has be en observed by low-temperature infrared transmission spectroscopy and room-temperature infrared phase-modulated ellipsometry. A band at 1730 cm (-1) accompanied by an increase of the amplitude of the bending mo de or a new broad band at similar to 870 cm (-1) was observed after 1 h of intense illumination of an annealed a-Si:H sample. A shift to low er frequencies of this band is observed with prolonged light-soaking t ime and the band disappears after similar to 4h of illumination. At th e same time the density of atomic hydrogen bonded to silicon decreases , as inferred from the area under the broad band at similar to 640 cm( -1). Our results can be interpreted by a hydrogen diffusion model in w hich the hydrogen atom of a Si-H bond next to a weak Si-Si bond diffus es to form a three-centre bond at intermediate illumination times, the n diffuses further to form a stable Si-H bond at longer times.