Critical comparison of light-induced changes in sub-band-gap absorption and photoconductivity in hydrogenated amorphous silicon

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Abstract
This work compares changes in the density of states due to light‐induced degradation estimated by photoconductivity with those measured by photothermal deflection spectroscopy (PDS) on a series of hydrogenated amorphous silicon (a‐Si:H) films having different valence bandtail widths (E0 ). We find that the photoconductivity measurements indicate orders of magnitude larger defect density changes than do the PDS measurements as the valence bandtail becomes broader. This conflict is resolved by showing that this difference is due to changes in the recombination rate coefficient K with valence bandtail width. The absolute change in K increases exponentially with E0. However, the change in K relative to the K of the annealed state decreases with E0, explaining why poor material shows a smaller light‐induced effect.