Towards understanding persistent photoconductance in doping modulated amorphous silicon

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Abstract
We present a simple model to explain the origin of the persistent photoconductance (PPC) in p–n–p–n multilayers made of hydrogenated amorphous silicon: brief light exposures create metastable Staebler-Wronski defects in the p-type material, making it more intrinsic. This in turn pushes the Fermi level of the whole multilayer closer to the conduction band, thus causing the observed metastable increase of the electron dominated coplanar conductance of the multilayer. Much longer light exposures are needed to shift the Fermi level towards midgap due to Staebler-Wronski defects in the n-type layers, leading to a consequent decrease in the PPC effect. In support of our model we present experimental results on the creation rate and annealing kinetics of the light-induced metastable conductance changes in a multilayer and in p-type and n-type single layers.