Critical comparison of lighthyphen;induced changes in subhyphen;bandhyphen;gap absorption and photoconductivity in hydrogenated amorphous silicon

摘要

This work compares changes in the density of states due to lighthyphen;induced degradation estimated by photoconductivity with those measured by photothermal deflection spectroscopy (PDS) on a series of hydrogenated amorphous silicon (ahyphen;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 coefficientKwith valence bandtail width. The absolute change inKincreases exponentially withE0. However, the change inKrelative to theKof the annealed state decreases withE0, explaining why poor material shows a smaller lighthyphen;induced effect.