Nature of nonsubstitutional dopant states and the carrier-density statistics in hydrogenated amorphous silicon

A model for the electronic structure of group-III and -V dopants in tetrahedrally bonded amorphous semiconductors is presented. Based on this model and the charge-neutrality relation appropriate for amorphous solids, the experimental observation of the carrier-density increase with doping level in compensatively doped $a-\mathrm{S}\mathrm{i}:\mathrm{H}$ can be explained as a consequence of a significant density of donorlike and/or acceptorlike states near the Fermi level.