Surface metastable layer in amorphous silicon and its influence on material photoconductivity and electronic stability

Light-induced reversible changes in the a-Si:H surface microstructure have been detected with a new method based on the joint analysis of spectral ellipsometric and photometric measurements. These changes consist in the growth of a thin surface overlayer with light soaking correlated with a planar photoconductivity degradation. Some (small) systematic increase in the photoconductivity (but not in the dark conductivity) of as-deposited and light-soaked samples after the chemical etching of the surface with alkaline has also been found. However, numerical simulation indicates that the contribution of surface defects to planar conductivity reduction has to be much less compared to the bulk ones, and their effect in devices is expected to be stronger. In addition, we show that a thin layer with high trap concentration has to occur near the top n/i-interface in n-i-n-structures. The origin of the layer may be related to a hydrogen rearrangement (or reconfiguration)