Effect of the surface condition on the conductance of hydrogenated amorphous silicon

We observed that the conductance of undoped hydrogenated amorphous silicon films (a-Si:H) is dominated by an electron accumulation layer at their surface. With increasing oxide thickness the band bending diminishes and then converts to hole accumulation. The surface changes from n type to p type as the result of light exposure. The surface space-charge layer was tested and changed by adsorbate layers of water and oxygen and layers of evaporated Se. It is found that erroneous conclusions will be drawn about the values of the conductivity activation energy, the prefactor, and the Meyer–Neldel relation between these parameters unless the conduction in the surface space-charge layer is eliminated or accounted for.