Fast metastable defect-creation in amorphous silicon by femtosecond light pulses

The creation of metastable dangling-bond defects in hydrogenated amorphous silicon subjected to short, intense laser pulses is investigated. It is found that pulse excitation leads to an order-of-magnitude increase in the defect creation rate compared to continuous illumination with the same average photon flux and photon energy. This implies that metastable-defect formation depends superlinearly on the density of photoexcited carriers. The much larger defect creation rate in the case of pulse excitation allows us to clarify the origin of saturation effects in the metastable-defect density, that are important for an assesment of the long-term conversion efficiency of amorphous-silicon solar cells.