Carrier Recombination Times in Amorphous-Silicon Doping Superlattices

Doping superlattices, i.e., multilayer structures consisting of ultrathin ($50 \AA <~d<~400 \AA$) $n$-type, intrinsic, and $p$-type layers of $a$-Si: H (nipi structures), have been produced. Up to a tenfold increase in their infrared photoconductivity after band-gap illumination compared to unstructured $a$-Si: H is observed. The results are well described by a simple model for the carrier recombination kinetics that takes into account the spatial separation of electrons and holes due to the modulation of the band energies.