Frequency-dependent loss in sandwich samples of hydrogenated amorphous silicon

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Abstract
Measurements of the a.c. conductivity of intrinsic sandwich samples of a-Si: H with n+ contact layers made between 1.3 and 360 K are described. Effects arising from the series impedance of the n+ layers are described by a simple geometrical model, demonstrating that the losses observed are representative of the bulk material. At low temperatures, the loss is small and fairly independent of temperature, but above 80 K it increases rapidly with temperature. The low-temperature loss is ascribed to deep states, and that occurring at higher temperatures to band-tail relaxation. Evidence in favour of this view is presented from the changes in loss observed under illumination.