Photodegradation for a hydrogenated amorphous silicon photoconversion layer in a solid-state image sensor

Photodegradation for a hydrogenated amorphous silicon photoconversion layer in a two-level solid-state imaging device was studied. The residual current after a light pulse, which causes image lag for the imaging device, was most sensitive to light exposure among several properties, so that the residual current determines the lifetime for the photoconversion layer. The space charge was also increased with increasing residual current by light exposure, because both properties reflected light-induced defect states. The space charge was found to be a good monitor for the photodegradation. The space-charge density had light intensity and exposure-time dependency, which is similar to that for dangling bond density. The lifetime for the photoconversion layer, which was evaluated through the space-charge density change, was 1.5×10⁷ h under standard illumination for the imager. This lifetime is sufficiently long for practical imager use