A detailed investigation was made of the spatial distribution of dangling bonds in light-soaked hydrogenated amorphous films. The results of light soaking, using different light intensities (3 or 0.3W/cm2), showed that an inverse power-law dangling bond distribution existed; regardless of the light-soaking intensity. The exponent of the inverse power distribution was equal to about 0.6. The non-uniform spatial distribution of the dangling bonds in light-soaked amorphous hydrogenated material was suggested to arise from a non-uniform distribution of photo-carriers during light-soaking, rather than from an inhomogeneity of the material. The same annealing behavior of light-induced dangling bonds was observed, regardless of the thickness of the sample and regardless of whether the sample was light-soaked from one side or from both sides. This, together with the observation of identical spin characteristics, indicated that the light-induced dangling bonds at various depths of a given sample were identical in nature. The surface dangling-bond density was found to be much less sensitive to light soaking than was the bulk dangling-bond density, and could be assumed to be unchanged if the light-soaking intensity was not much higher than 0.3W/cm2 and the light-soaking time was shorter than some 10h. It was shown that the conventional method for estimating the surface dangling-bond density was not suitable for light-soaked amorphous hydrogenated material; due to the highly non-uniform distribution of dangling bonds in the material. The non-uniform distribution of dangling bonds could lead to significant disagreements between various techniques for quantifying the Staebler-Wronski effect.

J.H.Zhou, M.Kumeda, T.Shimizu: Physical Review B, 1996, 53[11], 7267-74