Voltage-induced anomalies in the coplanar conductance of amorphous semiconductor-insulator multilayers

The electrical properties of compositionally modulated multilayer films consisting of hydrogenated amorphous silicon (a-Si:H) and amorphous silicon nitride (a-SiNₓ:H) possess several anomalies that are not observed in unlayered a-Si:H films. Long time constants and an increase in coplanar dark conductance are observed when a moderately large bias is applied to the samples. A brief exposure to light while the sample is under bias further increases the dark conductance. This metastable state lasts for hours and can be removed either by annealing at higher temperatures or by a brief exposure to light with no bias applied. The results are explained by charge accumulation in the semiconductor layers due to the potential difference across the insulating layers. This happens when the inhomogeneities in the a-Si:H layers produce different potential profiles of the applied bias in adjacent a-Si:H layers.