Doping and gap states in amorphous silicon

Abstract

The author shows that the decline in doping efficiency in a-Si:H with increased doping level arises because the dopants act as negative U centres and pin Ef during deposition. He also shows that only deep states from dangling bonds and dopants respond to coordination changes so unlike in chalcogenides, Ef is pinned in a finite density of shallow tail states. Defect bonding can now be expressed in a single scheme valid for all amorphous semiconductors.