Hydrogen diffusion, evolution and rehydrogenation

The ability of hydrogen to move into, out of, and within a-Si H has both beneficial and undesirable properties. The low defect density is a beneficial result of the bonding of hydrogen to weak or 

Diffusion occurs when there is a gradient of the chemical potential. In a uniform bulk material, the chemical potential depends only on the concentration, C, resulting in Pick s law of diffusion. 

The hydrogen diffusion coefficients shown in Pig. 2.20 are thermally activated. 

Thermally activated diffusion is explained by a trapping mechanism. Almost all the hydrogen is bonded to silicon atoms which do not diffuse significantly at these temperatures, so that hydrogen diffusion occurs by breaking a Si—H bond and reforming the bond at a new site. The 

5 eV diffusion activation energy, needed to release hydrogen from the Si—H bond into an interstitial site, is smaller than the 

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