The migration of D was investigated by performing experiments in which the D source was either a remote atomic D plasma or a deuterated amorphous layer (table 59). Enhanced diffusion, and a considerably lower activation energy, was observed in the case of diffusion from a plasma. This behavior was attributed to the saturation of D configurations with a high binding energy. These acted as deep D traps and controlled transport during diffusion from a deuterated layer, but were used up by D atoms which were injected from the plasma. The diffusion from a plasma was then governed by hopping through states with a low binding energy. A density of states distribution was deduced for the configurations which controlled diffusion. This consisted partly of a shallow state in which the D was weakly bonded and could diffuse with an activation energy of 0.5eV. There were also deep states, for which the binding energy was greater than 1.2eV, and which had a total density of about 1022/cm3. In the case of glow-discharge hydrogenated amorphous material, the D was bonded to deep states and only 20 to 60% of these states were empty.

Trap-Limited Hydrogen Diffusion in a-Si:H. P.V.Santos, W.B.Jackson: Physical Review B, 1992, 46[8], 4595-606

Table 59

Diffusivity of D in Si