The relationship between electronic carriers and H migration in amorphous hydrogenated material was investigated by using secondary ion mass spectrometry to measure D diffusion profiles in the intrinsic layer of p-i-n photodiodes. The carrier concentration in the i-layer was controlled by varying the temperature, the illumination intensity, or the bias which was applied to the devices. It was demonstrated that H migration was controlled by an electronic mechanism, and was enhanced when the carrier population was increased by illumination. It was suppressed when the population was reduced to below the thermal equilibrium value by applying a reverse bias to the diodes. This effect was attributed to the dependence upon carrier density of the dissociation rate of H from Si-H bonds and into the diffusion path, which consisted of interstitial sites. In addition, the migration length in the diffusion path increased under a reverse bias. The enhanced migration was associated with a decrease in the effective density of traps for H in a carrier-depleted layer. The trap density under these conditions was close to the dangling-bond density. This suggested that the migration length was governed by capture into these defects.

P.V.Santos, N.M.Johnson, R.A.Street, M.Hack, R.Thompson, C.C.Tsai: Physical Review B, 1993, 47[16], 10244-60