Silicon Network Relaxation in Amorphous Hydrogenated Silicon

We have investigated nanovoid-free, low-defect-density, amorphous hydrogenated silicon, a-Si:H, with variable hydrogen content. We have observed reconstruction of all silicon-silicon bonds at temperatures as low as 430 degrees C, well below the crystallization temperature. This bond reconstruction leads to a decrease in thin-film thickness and an increase in material density, about 3% for thematerial with 9 at. % of hydrogen, during slow hydrogen outdiffusion. These results suggest that a long-range structural rearrangement of the silicon network can occur simultaneously with hydrogen motion and this has important consequences for all metastability models in amorphous hydrogenated silicon.