Light-induced long-range hydrogen motion in hydrogenated amorphous silicon at room temperature

We present evidence for long-range hydrogen motion in hydrogenated amorphous silicon (a-Si:H) under room-temperature illumination, by monitoring the changes in the Raman spectrum of an a-WO3 overlayer with illumination. We observe that illumination causes hydrogen to diffuse out of the a-Si:H layer into the a-WO3 layer. This hydrogen motion is observed to saturate after about 30 min when the a-Si:H is illuminated with 15 W/cm2 of the 514.5 nm laser line at room temperature. The amount of hydrogen that diffuses out of the a-Si:H layer is estimated semiquantitatively to be approximately 9×10−4 at. %.