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Abstract
The influence of adsorbates such as water and ammonia on the electrical conductance of hydrogenated amorphous silicon, a-Si: H, has been studied as a function of doping, temperature, thickness, surface oxidation and light exposure. Adsorbates are found to cause large conductance changes in heat-dried specimens; the original state of conductance can be restored by heating the samples above 150°C in vacuum. A model is proposed in which the adsorbate effects are the consequence of charge exchange between the adsorbate and the semiconductor. Using a numerical calculation based on this model, the number of photocreated defect states produced by the Staebler-Wronski effect has been estimated.